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2022 Volume 38 Issue 3
2022, 38(3): 190707
doi: 10.3866/PKU.WHXB201907076
Abstract:
Resistive switching devices have the advantage that the resistance can be repeatedly regulated between two or more resistance states. As a new resistive switching device, a memristor has abundant resistance states that can be continuously tuned. In recent years, memristors have been extensively studied for emerging nonvolatile memories and in the construction of neuromorphic systems owing to their simple two-terminal structure, high integration, and low operating voltage compared with those of traditional metal-oxide-semiconductor field-effect transistors. However, their application is limited owing to their relatively poor reliability. Recently, several studies have shown that two-dimensional materials such as graphene oxide can optimize the memristor performance. A new two-dimensional material, MXene, also exhibits special mechanical and electrical properties that show promise for use in memristors owing to its two-dimensional layered structure similar to that of graphene. MXene is a two-dimensional transition metal carbide/nitride of the form Mn+1Xn, where M is an early transition metal and X is carbon or nitrogen. Its other characteristics such as hydrophilic surfaces and ultrahigh metal conductivity (6000–8000 S·cm-1) have been studied, and it has been applied to energy storage devices and electronic devices such as supercapacitors and secondary batteries. However, the application of MXene in resistive devices has been rarely investigated, especially for memristors. In this study, we prepared Ti3C2 powder by etching layered compounds of Ti3AlC2 with a mixture of HCl and HF. Next, Ti3C2 film was introduced into the memristor structure by spin-coating. The physical characteristics of Ti3C2 were investigated and analyzed by X-ray diffraction and scanning electron microscopy, and a memristor with Cu/Ti3C2/SiO2/W structure was fabricated. In this structure, Ti3C2 and SiO2 were introduced as resistive layers, and related electrical properties were investigated. Under dual DC voltage sweeping, the typical switching characteristic curves of the memristor were measured. Moreover, the repeatability and stability of high- and low-resistance states were investigated and analyzed, respectively. The experimental results show that the device can maintain stable high- and low-resistance states for > 104 s during 100 dual-voltage sweeping cycles. In addition, the device can be regulated by a pulse voltage and realize typical paired-pulse facilitation that is similar to biological synapses. This work proved that the Cu/Ti3C2/SiO2/W memristor has huge potential for application in the construction of emerging memory devices and artificial neuromorphic systems. ![]()
Resistive switching devices have the advantage that the resistance can be repeatedly regulated between two or more resistance states. As a new resistive switching device, a memristor has abundant resistance states that can be continuously tuned. In recent years, memristors have been extensively studied for emerging nonvolatile memories and in the construction of neuromorphic systems owing to their simple two-terminal structure, high integration, and low operating voltage compared with those of traditional metal-oxide-semiconductor field-effect transistors. However, their application is limited owing to their relatively poor reliability. Recently, several studies have shown that two-dimensional materials such as graphene oxide can optimize the memristor performance. A new two-dimensional material, MXene, also exhibits special mechanical and electrical properties that show promise for use in memristors owing to its two-dimensional layered structure similar to that of graphene. MXene is a two-dimensional transition metal carbide/nitride of the form Mn+1Xn, where M is an early transition metal and X is carbon or nitrogen. Its other characteristics such as hydrophilic surfaces and ultrahigh metal conductivity (6000–8000 S·cm-1) have been studied, and it has been applied to energy storage devices and electronic devices such as supercapacitors and secondary batteries. However, the application of MXene in resistive devices has been rarely investigated, especially for memristors. In this study, we prepared Ti3C2 powder by etching layered compounds of Ti3AlC2 with a mixture of HCl and HF. Next, Ti3C2 film was introduced into the memristor structure by spin-coating. The physical characteristics of Ti3C2 were investigated and analyzed by X-ray diffraction and scanning electron microscopy, and a memristor with Cu/Ti3C2/SiO2/W structure was fabricated. In this structure, Ti3C2 and SiO2 were introduced as resistive layers, and related electrical properties were investigated. Under dual DC voltage sweeping, the typical switching characteristic curves of the memristor were measured. Moreover, the repeatability and stability of high- and low-resistance states were investigated and analyzed, respectively. The experimental results show that the device can maintain stable high- and low-resistance states for > 104 s during 100 dual-voltage sweeping cycles. In addition, the device can be regulated by a pulse voltage and realize typical paired-pulse facilitation that is similar to biological synapses. This work proved that the Cu/Ti3C2/SiO2/W memristor has huge potential for application in the construction of emerging memory devices and artificial neuromorphic systems.
2022, 38(3): 191205
doi: 10.3866/PKU.WHXB201912052
Abstract:
Although there has been great progress, the commercialization of proton exchange membrane fuel cells (PEMFCs) is still hindered by high cost due to the use of Pt catalysts. Furthermore, structural improvement of the catalyst layers is limited by inadequate studies of the ultrathin perfluorosulfonic acid ionomer (e.g., Nafion ionomer) film in the catalyst layers. During the preparation of the catalyst ink, the dispersion solvent affects the morphology of Nafion ionomers, which affects the microstructure and proton conduction behavior of the Nafion thin film wrapped on the surface of the catalyst particles after the catalyst layer is formed. To simulate the aggregation of ionomers in the catalyst layer, a self-assembly technology was used to obtain nanoscale Nafion thin films with precise and controllable thickness on a SiO2 model substrate. The proton conductivity and microstructure of the Nafion thin films were obtained through electrochemical impedance spectroscopy and a series of micro-characterization methods. Furthermore, the relationship between proton conduction behavior within ultrathin Nafion films and colloidal morphology in Nafion solution was studied using different organic solvents. The goal was to explore and establish the microstructure model of nanoscale Nafion thin films through micro-characterization technologies, such as nuclear magnetic resonance and dynamic light scattering. It was found that at the nanoscale, Nafion thin films (~40 nm) result in low proton conductivity; an order of magnitude lower than that of bulk membranes (~10–100 μm). However, replacing iso-propanol with n-butanol (which has a lower dielectric constant) as the dispersion media of the Nafion ionomer improved the proton conductivity of the Nafion thin films. This is because Nafion in solvents with a lower dielectric constant possesses higher main chain solubility and mobility. Thus, Nafion molecules more easily aggregate into large rod-shaped micelles, which is beneficial to the construction of proton conduction channels after the self-assembly process. Furthermore, the electrostatic force between Nafion aggregates and the substrate in solvents with lower dielectric constant is smaller. This means more sulfonic groups are involved in the formation of proton conduction channels that in turn improve the proton conductivity of the Nafion thin film. In general, Nafion in solvents with lower dielectric constant leads to a structure that can facilitate proton conduction. This study provides guidance for optimizing the structure of ultrathin Nafion films and improving the proton conduction in the catalyst layers of PEMFCs. ![]()
Although there has been great progress, the commercialization of proton exchange membrane fuel cells (PEMFCs) is still hindered by high cost due to the use of Pt catalysts. Furthermore, structural improvement of the catalyst layers is limited by inadequate studies of the ultrathin perfluorosulfonic acid ionomer (e.g., Nafion ionomer) film in the catalyst layers. During the preparation of the catalyst ink, the dispersion solvent affects the morphology of Nafion ionomers, which affects the microstructure and proton conduction behavior of the Nafion thin film wrapped on the surface of the catalyst particles after the catalyst layer is formed. To simulate the aggregation of ionomers in the catalyst layer, a self-assembly technology was used to obtain nanoscale Nafion thin films with precise and controllable thickness on a SiO2 model substrate. The proton conductivity and microstructure of the Nafion thin films were obtained through electrochemical impedance spectroscopy and a series of micro-characterization methods. Furthermore, the relationship between proton conduction behavior within ultrathin Nafion films and colloidal morphology in Nafion solution was studied using different organic solvents. The goal was to explore and establish the microstructure model of nanoscale Nafion thin films through micro-characterization technologies, such as nuclear magnetic resonance and dynamic light scattering. It was found that at the nanoscale, Nafion thin films (~40 nm) result in low proton conductivity; an order of magnitude lower than that of bulk membranes (~10–100 μm). However, replacing iso-propanol with n-butanol (which has a lower dielectric constant) as the dispersion media of the Nafion ionomer improved the proton conductivity of the Nafion thin films. This is because Nafion in solvents with a lower dielectric constant possesses higher main chain solubility and mobility. Thus, Nafion molecules more easily aggregate into large rod-shaped micelles, which is beneficial to the construction of proton conduction channels after the self-assembly process. Furthermore, the electrostatic force between Nafion aggregates and the substrate in solvents with lower dielectric constant is smaller. This means more sulfonic groups are involved in the formation of proton conduction channels that in turn improve the proton conductivity of the Nafion thin film. In general, Nafion in solvents with lower dielectric constant leads to a structure that can facilitate proton conduction. This study provides guidance for optimizing the structure of ultrathin Nafion films and improving the proton conduction in the catalyst layers of PEMFCs.
2022, 38(3): 200100
doi: 10.3866/PKU.WHXB202001007
Abstract:
Lithium-ion batteries are the most widely used energy storage device owing to their advantages such as high energy density, high cycle life, and low self-discharge rate. Because two-dimensional (2D) materials are commonly used as anode materials, the study of their lithiation behaviors is significant for improving the energy density and cycle life of batteries. Although some spectroscopic methods have been developed for studying the intercalation/deintercalation process of lithium in graphene, a new characterization technique that can directly investigate ion diffusion pathways at a microscale level would be beneficial to provide more detailed information on the mechanism of electrochemical reactions. It is an efficient solution to utilize the high spatial resolution of microscopic characterization to study the microscale electrochemical process. For this purpose, it becomes necessary to develop special specimens and setups that can undergo electrochemical experiments and are also compatible with microscopic characterization techniques. Herein, we developed a new planar micro-battery architecture on a SiO2-coated silicon substrate that can be used to study the lithiation behaviors of various 2D materials using the micro-Raman mapping technique. In this planar micro-battery, the mechanically exfoliated few-layer graphene was used as the positive electrode, the thermal-evaporated lithium metal was employed as the negative electrode, and the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide with lithium bis(trifluoromethane)sulfonimide was used as the electrolyte. The micro-battery was tested using the galvanostatic discharge method on a probe station in an argon glove box. The selected lab-on-chip solution makes the lithiation of graphene observable under the micro-Raman spectroscope with a high spatial resolution. Raman mapping was successfully performed and graphene G-band signals were observed. Based on the facts that a small amount of lithium intercalation in graphene induces a blueshift of its G-band, and a large amount of lithium intercalation induces the splitting of the G-band into G- and G+, we can correlate the degree of lithiation in graphene with its G-band signals and thus monitor the lithium intercalation process on graphene in the planar micro-battery. The time-dependent lithium distribution in graphene at different discharge stages could be obtained by comparing the G-band Raman mapping images to the corresponding optical micrographs. On the basis of these analyses, it was found that lithium ions diffuse between the layers in graphene and terminate at the graphene fault. These results help us understand the diffusion process of lithium in the graphene electrode during discharge. Moreover, the as-developed micro-battery is compatible with more characterization methodologies, such as optical microscopy, electrical transport, and electron microscopy, providing a broad application platform. ![]()
Lithium-ion batteries are the most widely used energy storage device owing to their advantages such as high energy density, high cycle life, and low self-discharge rate. Because two-dimensional (2D) materials are commonly used as anode materials, the study of their lithiation behaviors is significant for improving the energy density and cycle life of batteries. Although some spectroscopic methods have been developed for studying the intercalation/deintercalation process of lithium in graphene, a new characterization technique that can directly investigate ion diffusion pathways at a microscale level would be beneficial to provide more detailed information on the mechanism of electrochemical reactions. It is an efficient solution to utilize the high spatial resolution of microscopic characterization to study the microscale electrochemical process. For this purpose, it becomes necessary to develop special specimens and setups that can undergo electrochemical experiments and are also compatible with microscopic characterization techniques. Herein, we developed a new planar micro-battery architecture on a SiO2-coated silicon substrate that can be used to study the lithiation behaviors of various 2D materials using the micro-Raman mapping technique. In this planar micro-battery, the mechanically exfoliated few-layer graphene was used as the positive electrode, the thermal-evaporated lithium metal was employed as the negative electrode, and the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide with lithium bis(trifluoromethane)sulfonimide was used as the electrolyte. The micro-battery was tested using the galvanostatic discharge method on a probe station in an argon glove box. The selected lab-on-chip solution makes the lithiation of graphene observable under the micro-Raman spectroscope with a high spatial resolution. Raman mapping was successfully performed and graphene G-band signals were observed. Based on the facts that a small amount of lithium intercalation in graphene induces a blueshift of its G-band, and a large amount of lithium intercalation induces the splitting of the G-band into G- and G+, we can correlate the degree of lithiation in graphene with its G-band signals and thus monitor the lithium intercalation process on graphene in the planar micro-battery. The time-dependent lithium distribution in graphene at different discharge stages could be obtained by comparing the G-band Raman mapping images to the corresponding optical micrographs. On the basis of these analyses, it was found that lithium ions diffuse between the layers in graphene and terminate at the graphene fault. These results help us understand the diffusion process of lithium in the graphene electrode during discharge. Moreover, the as-developed micro-battery is compatible with more characterization methodologies, such as optical microscopy, electrical transport, and electron microscopy, providing a broad application platform.
2022, 38(3): 200203
doi: 10.3866/PKU.WHXB202002032
Abstract:
Carbon dots (CDs), as a kind of carbon-based fluorescent nanodots (FNDs), not only retain the advantageous characteristics of carbon-based materials (e.g., low toxicity and biocompatibility) but also exhibit tunable fluorescence emission, low photobleaching, and undergo facile surface functionalization. Therefore, the prospect of applying these materials for analysis and detection, cell imaging, drug delivery, light-emitting devices, photocatalysis, biosensing, and cancer treatment is promising. Although the synthesis of carbon dots from green and renewable feedstocks as biomass carbon sources is possible, the controllability of the involved chemical reactions is poor, resulting in poor atom economy, low quantum yields, and, especially, extremely low yields of carbon dots. In addition, these disadvantages could lead to an increase in equipment requirements and could pose a safety risk because of the need for hydrothermal and solvothermal synthesis. Certain methods even require large amounts of acid/alkali, strong oxidants, or organic solvents, thereby complicating the post-processing process and generating waste and emissions. This research aimed to implement a new idea, namely to "fabricate" rather than "synthesize" carbon-based FNDs from a certain kind of natural and small unsaturated molecule with surface activity relying on a self-assembling and self-crosslinking strategy in lieu of traditional approaches that involve uncontrollable reactions with unknown mechanisms including pyrolysis, dehydrolysis, polyconcensation, and carbonization. In this context, conjugated linoleic acid (CLA) has been studied extensively in our laboratory, and was found to have the self-assembly and self-crosslink characteristics required by the above innovative strategy. This motivated us to adopt CLA as a new carbon source in this study. First, CLA self-assembles into unsaturated fatty acid liposomes (ufasomes) in an aqueous solution of pH 8.6 at ambient temperature (15-25 ℃), and then, the initiator Ammonium persulfate is added to induce self-crosslinking of the ufasomes at 80 ℃ to obtain firm and uniform nanoparticles. On this basis, the possibility of using them as FNDs is investigated. Consequently, FNDs based on self-crosslinked ufasomes (SCU-FNDs) are prepared in high FND yield of 73.9% after dialysis, with a consistent particle size (17 nm), a degree of self-crosslink (DSC) of 75%, and emission of bluish green fluorescence excited at 320 nm. Furthermore the "fabrication" route provided a clear solution of FNDs that could be applied directly without separation and purification and with no wasteful emissions, which is therefore beneficial for large-scale preparation. The experimental results showed that the fluorescence intensities of the SCU-FNDs are positively correlated with both the surface carboxyl groups and DSC results. A reasonable explanation for the former relationship is the effect of the restricted geometry of the ufasomes on the accumulation of oxygen atoms at the surface of FNDs, whereas the latter could be explained by the confinement effect of the covalent crosslink on the motion of the hydrocarbon chain of the CLA molecules. The experimental results also showed that the SCU-FNDs have temperature-sensitive fluorescence properties, which is attributed to the motion of the residual hydrocarbon chain inside the SCU-FNDs even though they have been locally polymerized. The change in the fluorescence intensity of the FNDs as a function of the temperature was good in accordance with the linear relationship I/I0 = -0.00922T + 1.229 (R2 = 0.99) in the range of 25-85 ℃, which demonstrates the potential for preparing green and safe undoped FNDs for use as biocompatible and temperature-sensitive fluorescent probes. ![]()
Carbon dots (CDs), as a kind of carbon-based fluorescent nanodots (FNDs), not only retain the advantageous characteristics of carbon-based materials (e.g., low toxicity and biocompatibility) but also exhibit tunable fluorescence emission, low photobleaching, and undergo facile surface functionalization. Therefore, the prospect of applying these materials for analysis and detection, cell imaging, drug delivery, light-emitting devices, photocatalysis, biosensing, and cancer treatment is promising. Although the synthesis of carbon dots from green and renewable feedstocks as biomass carbon sources is possible, the controllability of the involved chemical reactions is poor, resulting in poor atom economy, low quantum yields, and, especially, extremely low yields of carbon dots. In addition, these disadvantages could lead to an increase in equipment requirements and could pose a safety risk because of the need for hydrothermal and solvothermal synthesis. Certain methods even require large amounts of acid/alkali, strong oxidants, or organic solvents, thereby complicating the post-processing process and generating waste and emissions. This research aimed to implement a new idea, namely to "fabricate" rather than "synthesize" carbon-based FNDs from a certain kind of natural and small unsaturated molecule with surface activity relying on a self-assembling and self-crosslinking strategy in lieu of traditional approaches that involve uncontrollable reactions with unknown mechanisms including pyrolysis, dehydrolysis, polyconcensation, and carbonization. In this context, conjugated linoleic acid (CLA) has been studied extensively in our laboratory, and was found to have the self-assembly and self-crosslink characteristics required by the above innovative strategy. This motivated us to adopt CLA as a new carbon source in this study. First, CLA self-assembles into unsaturated fatty acid liposomes (ufasomes) in an aqueous solution of pH 8.6 at ambient temperature (15-25 ℃), and then, the initiator Ammonium persulfate is added to induce self-crosslinking of the ufasomes at 80 ℃ to obtain firm and uniform nanoparticles. On this basis, the possibility of using them as FNDs is investigated. Consequently, FNDs based on self-crosslinked ufasomes (SCU-FNDs) are prepared in high FND yield of 73.9% after dialysis, with a consistent particle size (17 nm), a degree of self-crosslink (DSC) of 75%, and emission of bluish green fluorescence excited at 320 nm. Furthermore the "fabrication" route provided a clear solution of FNDs that could be applied directly without separation and purification and with no wasteful emissions, which is therefore beneficial for large-scale preparation. The experimental results showed that the fluorescence intensities of the SCU-FNDs are positively correlated with both the surface carboxyl groups and DSC results. A reasonable explanation for the former relationship is the effect of the restricted geometry of the ufasomes on the accumulation of oxygen atoms at the surface of FNDs, whereas the latter could be explained by the confinement effect of the covalent crosslink on the motion of the hydrocarbon chain of the CLA molecules. The experimental results also showed that the SCU-FNDs have temperature-sensitive fluorescence properties, which is attributed to the motion of the residual hydrocarbon chain inside the SCU-FNDs even though they have been locally polymerized. The change in the fluorescence intensity of the FNDs as a function of the temperature was good in accordance with the linear relationship I/I0 = -0.00922T + 1.229 (R2 = 0.99) in the range of 25-85 ℃, which demonstrates the potential for preparing green and safe undoped FNDs for use as biocompatible and temperature-sensitive fluorescent probes.
2022, 38(3): 200302
doi: 10.3866/PKU.WHXB202003026
Abstract:
Zirconium alloys are often used to fabricate nuclear fuel cladding and other structural materials because of their low thermal neutron absorption cross section, satisfactory corrosion resistance, and decent mechanical properties. The oxidation rate and hydrogen-absorption fraction of zirconium alloys can be reduced by adding moderate amount of Nb to them, and the corrosion resistance of zirconium alloys can be improved as well. Although the corrosion resistance of zirconium alloys has been widely recognized, the in situ study of zirconium alloys in conditions that resemble real oxidative-corrosion environments has still been a challenging subject. The initial oxidation behavior of zirconium alloys might affect the subsequent generation of oxides in the form of the element valence and type of surface oxides changes, resulting in the long-term corrosion-behavior changes. In addition, the reaction mechanism of Nb in zirconium alloys is still controversial. To investigate the influence of the alloy composition and environmental conditions on the initial oxidation behavior of zirconium alloys, in situ initial oxidation experiments were performed on two different Zr alloys in a near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) chamber. The samples were cut to the size of 12 mm × 3 mm, and the primary oxide film was removed via pickling, argon etching and annealing. Oxygen or water vapors with the pressure in the range of 1.3 × 10-8-1.3 × 10-1 mbar (1 mbar = 100 Pa) were gradually introduced into the NAP-XPS chamber after sample-surface cleaning. The experiment was repeated at room temperature (300 K) and 623 K. The results showed that both Nb-containing and Nb-free zirconium-alloy surfaces transitioned from a metallic state to various oxidation states during the initial oxidation process. The oxidation rates of both the alloys were lower in water vapors than those in oxygen. In the presence of water vapors or oxygen, both the alloys oxidized more slowly at room temperature than at 623 K. Compared with 1%Nb zirconium alloys, the Nb-free zirconium alloys were more easily oxidized and had a denser oxide layer, in the oxygen atmosphere at 623 K. To some extent, the presence of Nb would reduce the adsorption capacity of oxygen atoms. The oxidation rate of 1%Nb zirconium alloy was quick at room temperature and also at low water vapor pressures at 623 K; Nb promoted the formation of OH- at the surface. Under the high pressure vapor atmosphere at 623 K, the Nb-free zirconium alloys were more prone to be oxidized; Nb diffused to the surface at high temperatures and inhibited the breaking of the OH- bond; however, the surfaces of both the samples could not be completely oxidized in a short time. ![]()
Zirconium alloys are often used to fabricate nuclear fuel cladding and other structural materials because of their low thermal neutron absorption cross section, satisfactory corrosion resistance, and decent mechanical properties. The oxidation rate and hydrogen-absorption fraction of zirconium alloys can be reduced by adding moderate amount of Nb to them, and the corrosion resistance of zirconium alloys can be improved as well. Although the corrosion resistance of zirconium alloys has been widely recognized, the in situ study of zirconium alloys in conditions that resemble real oxidative-corrosion environments has still been a challenging subject. The initial oxidation behavior of zirconium alloys might affect the subsequent generation of oxides in the form of the element valence and type of surface oxides changes, resulting in the long-term corrosion-behavior changes. In addition, the reaction mechanism of Nb in zirconium alloys is still controversial. To investigate the influence of the alloy composition and environmental conditions on the initial oxidation behavior of zirconium alloys, in situ initial oxidation experiments were performed on two different Zr alloys in a near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) chamber. The samples were cut to the size of 12 mm × 3 mm, and the primary oxide film was removed via pickling, argon etching and annealing. Oxygen or water vapors with the pressure in the range of 1.3 × 10-8-1.3 × 10-1 mbar (1 mbar = 100 Pa) were gradually introduced into the NAP-XPS chamber after sample-surface cleaning. The experiment was repeated at room temperature (300 K) and 623 K. The results showed that both Nb-containing and Nb-free zirconium-alloy surfaces transitioned from a metallic state to various oxidation states during the initial oxidation process. The oxidation rates of both the alloys were lower in water vapors than those in oxygen. In the presence of water vapors or oxygen, both the alloys oxidized more slowly at room temperature than at 623 K. Compared with 1%Nb zirconium alloys, the Nb-free zirconium alloys were more easily oxidized and had a denser oxide layer, in the oxygen atmosphere at 623 K. To some extent, the presence of Nb would reduce the adsorption capacity of oxygen atoms. The oxidation rate of 1%Nb zirconium alloy was quick at room temperature and also at low water vapor pressures at 623 K; Nb promoted the formation of OH- at the surface. Under the high pressure vapor atmosphere at 623 K, the Nb-free zirconium alloys were more prone to be oxidized; Nb diffused to the surface at high temperatures and inhibited the breaking of the OH- bond; however, the surfaces of both the samples could not be completely oxidized in a short time.
2022, 38(3): 200303
doi: 10.3866/PKU.WHXB202003031
Abstract:
The environmental behaviours of actinides and fission products have been highly concerned due to their potential risks to human beings after entering the body through inhalation or food chains. The chemical reactions of actinides and fission products at mineral-water interface are the most important factors influencing the sorption, diffusion, migration and other processes of actinides and fission products in natural environments. Therefore, it is of great importance to investigate the chemical behaviours of these radioactive elements or nuclides in terms of environmental safety, especially in the area of safety assessment for geological disposal of high level radioactive wastes. However, the chemical behaviours of nuclides at mineral-water interface are complex and the investigations at a molecular level are challenging. To understand the chemical behaviours of trivalent actinides An(Ⅲ) in depth, non-radioactive Eu(Ⅲ) is used as an analogue of An(Ⅲ) due to their similar ionic sizes and chemical characteristics. In this study, batch sorption experiments and spectroscopic characterization methods were used to study the surface sorption species of Eu(Ⅲ) on montmorillonite and possible sorption mechanisms. We studied the effects of solid-liquid ratio, contacting time, ionic strength, pH, carbonate and phosphate on Eu(Ⅲ) sorption on montmorillonite. Our results indicated that the sorption percentage of Eu(Ⅲ) on montmorillonite was low in the range of pH 3.0 to 6.0, and much higher in the range of pH 7.0 to 10.0. The increase of ionic strength inhibited the sorption of Eu(Ⅲ) at low pH values, suggesting that the sorption of Eu(Ⅲ) on montmorillonite was mainly outer-sphere complexation in low pH conditions. Based on the results of fluorescence analysis, we can conclude that the sorption of Eu(Ⅲ) on montmorillonite is mainly outer-sphere complexation in low pH conditions, inner-sphere complexation in neutral pH conditions and surface induced precipitations in high pH conditions. Furthermore, we studied the sorption behaviours of Eu(Ⅲ) not only in montmorillonite/Eu(Ⅲ) binary system but also in montmorillonite/Eu(Ⅲ)/anion ternary system. Our results indicated that carbonate and phosphate could also influence the sorption of Eu(Ⅲ). Carbonate did not have an obvious influence on the sorption amount of Eu(Ⅲ), but it helped to change the surface sorption species of Eu(Ⅲ) on montmorillonite in high pH conditions. As for phosphate, although the sorption of phosphate onto montmorillonite was very weak, it could significantly enhance the sorption of Eu(Ⅲ) on montmorillonite. Because there were no reference data about fluorescence lifetime of Eu(Ⅲ)-phosphate species, we did XPS measurements and phosphate sorption experiments to find out the reason for phosphate enhancing effect. Our results proved that Eu(Ⅲ) precipitated as EuPO4 on the surface of montmorillonite resulting in the enhancement of Eu(Ⅲ) sorption. This work is expected to provide a deeper understanding of the chemical behaviours of trivalent actinides An(Ⅲ) at mineral-water interface and predict the migration of An(Ⅲ) in the environment. ![]()
The environmental behaviours of actinides and fission products have been highly concerned due to their potential risks to human beings after entering the body through inhalation or food chains. The chemical reactions of actinides and fission products at mineral-water interface are the most important factors influencing the sorption, diffusion, migration and other processes of actinides and fission products in natural environments. Therefore, it is of great importance to investigate the chemical behaviours of these radioactive elements or nuclides in terms of environmental safety, especially in the area of safety assessment for geological disposal of high level radioactive wastes. However, the chemical behaviours of nuclides at mineral-water interface are complex and the investigations at a molecular level are challenging. To understand the chemical behaviours of trivalent actinides An(Ⅲ) in depth, non-radioactive Eu(Ⅲ) is used as an analogue of An(Ⅲ) due to their similar ionic sizes and chemical characteristics. In this study, batch sorption experiments and spectroscopic characterization methods were used to study the surface sorption species of Eu(Ⅲ) on montmorillonite and possible sorption mechanisms. We studied the effects of solid-liquid ratio, contacting time, ionic strength, pH, carbonate and phosphate on Eu(Ⅲ) sorption on montmorillonite. Our results indicated that the sorption percentage of Eu(Ⅲ) on montmorillonite was low in the range of pH 3.0 to 6.0, and much higher in the range of pH 7.0 to 10.0. The increase of ionic strength inhibited the sorption of Eu(Ⅲ) at low pH values, suggesting that the sorption of Eu(Ⅲ) on montmorillonite was mainly outer-sphere complexation in low pH conditions. Based on the results of fluorescence analysis, we can conclude that the sorption of Eu(Ⅲ) on montmorillonite is mainly outer-sphere complexation in low pH conditions, inner-sphere complexation in neutral pH conditions and surface induced precipitations in high pH conditions. Furthermore, we studied the sorption behaviours of Eu(Ⅲ) not only in montmorillonite/Eu(Ⅲ) binary system but also in montmorillonite/Eu(Ⅲ)/anion ternary system. Our results indicated that carbonate and phosphate could also influence the sorption of Eu(Ⅲ). Carbonate did not have an obvious influence on the sorption amount of Eu(Ⅲ), but it helped to change the surface sorption species of Eu(Ⅲ) on montmorillonite in high pH conditions. As for phosphate, although the sorption of phosphate onto montmorillonite was very weak, it could significantly enhance the sorption of Eu(Ⅲ) on montmorillonite. Because there were no reference data about fluorescence lifetime of Eu(Ⅲ)-phosphate species, we did XPS measurements and phosphate sorption experiments to find out the reason for phosphate enhancing effect. Our results proved that Eu(Ⅲ) precipitated as EuPO4 on the surface of montmorillonite resulting in the enhancement of Eu(Ⅲ) sorption. This work is expected to provide a deeper understanding of the chemical behaviours of trivalent actinides An(Ⅲ) at mineral-water interface and predict the migration of An(Ⅲ) in the environment.
2022, 38(3): 191206
doi: 10.3866/PKU.WHXB201912061
Abstract:
With the increasing demand for safe high energy density energy storage systems, solid-state lithium metal batteries have attracted extensive attention. The solid electrolyte, which is expected to replace the traditional liquid organic electrolyte core in solid-state lithium metal batteries because of its excellent mechanical properties and non-flammability. Lithium-ion solid-state electrolytes can be categorized into two broad types: inorganic electrolytes and polymer electrolytes. Inorganic solid electrolytes have the advantages of high room-temperature ionic conductivity, wide electrochemical window, and high mechanical strength. However, their high brittleness, high solid-solid interface contact resistance, complex preparation process, and high cost make future development and practical applications challenging. In contrast to inorganic electrolytes, polymer electrolytes are easy to process and exhibit better flexibility and easy formation of a good, stable interface with lithium metal. However, solid polymer electrolytes still exhibit insufficient ionic conductivity at room temperatures compared with polymer solid electrolytes. Therefore, neither the inorganic electrolytes nor the polymer electrolytes alone can meet the requirements of high-performance solid-state lithium metal batteries. Recently, dispersing ceramic fillers (especially fast lithium-ion conductors) in a polymer matrix to integrate with composite polymer electrolytes has been developed as an effective strategy for enhancing room-temperature ionic conductivity, mechanical properties, and thermal stability of solid polymer electrolytes. Inorganic fillers do not only reduce the polymer matrix crystallization but also improve the lithium-ion conductivity by promoting the dissociation of lithium salts. The Lewis acid-base groups and oxygen vacancy at the surface of inorganic fillers can increase the migration number of lithium ions. Nevertheless, the effect of the percolation structure of inorganic fillers on the conductivity of organic-inorganic composite electrolytes should be discussed. It is believed that the organic-inorganic interface is the main reason for the significantly enhanced lithium-ion conductivity of composite electrolytes based on the percolation theory. In this paper, from the perspective of percolation structure design, we summarize the progress on high lithium-ion conductive organic-inorganic composite electrolytes with different dimensional-structured inorganic fillers. From one-dimensional filler to three-dimensional filler, the ionic conductivity of a composite electrolyte can be significantly influenced by the rational design and optimization of the percolation structure and orientation of the inorganic filler. Vertically aligned inorganic fillers provide optimal ion transport pathways in the polymer matrix, significantly improving the lithium-ion conductivity of the composite electrolytes. Furthermore, the advantages and disadvantages of the different percolation structures are compared and discussed objectively. Finally, future development trends of organic-inorganic composite electrolytes are discussed. ![]()
With the increasing demand for safe high energy density energy storage systems, solid-state lithium metal batteries have attracted extensive attention. The solid electrolyte, which is expected to replace the traditional liquid organic electrolyte core in solid-state lithium metal batteries because of its excellent mechanical properties and non-flammability. Lithium-ion solid-state electrolytes can be categorized into two broad types: inorganic electrolytes and polymer electrolytes. Inorganic solid electrolytes have the advantages of high room-temperature ionic conductivity, wide electrochemical window, and high mechanical strength. However, their high brittleness, high solid-solid interface contact resistance, complex preparation process, and high cost make future development and practical applications challenging. In contrast to inorganic electrolytes, polymer electrolytes are easy to process and exhibit better flexibility and easy formation of a good, stable interface with lithium metal. However, solid polymer electrolytes still exhibit insufficient ionic conductivity at room temperatures compared with polymer solid electrolytes. Therefore, neither the inorganic electrolytes nor the polymer electrolytes alone can meet the requirements of high-performance solid-state lithium metal batteries. Recently, dispersing ceramic fillers (especially fast lithium-ion conductors) in a polymer matrix to integrate with composite polymer electrolytes has been developed as an effective strategy for enhancing room-temperature ionic conductivity, mechanical properties, and thermal stability of solid polymer electrolytes. Inorganic fillers do not only reduce the polymer matrix crystallization but also improve the lithium-ion conductivity by promoting the dissociation of lithium salts. The Lewis acid-base groups and oxygen vacancy at the surface of inorganic fillers can increase the migration number of lithium ions. Nevertheless, the effect of the percolation structure of inorganic fillers on the conductivity of organic-inorganic composite electrolytes should be discussed. It is believed that the organic-inorganic interface is the main reason for the significantly enhanced lithium-ion conductivity of composite electrolytes based on the percolation theory. In this paper, from the perspective of percolation structure design, we summarize the progress on high lithium-ion conductive organic-inorganic composite electrolytes with different dimensional-structured inorganic fillers. From one-dimensional filler to three-dimensional filler, the ionic conductivity of a composite electrolyte can be significantly influenced by the rational design and optimization of the percolation structure and orientation of the inorganic filler. Vertically aligned inorganic fillers provide optimal ion transport pathways in the polymer matrix, significantly improving the lithium-ion conductivity of the composite electrolytes. Furthermore, the advantages and disadvantages of the different percolation structures are compared and discussed objectively. Finally, future development trends of organic-inorganic composite electrolytes are discussed.
2022, 38(3): 200201
doi: 10.3866/PKU.WHXB202002017
Abstract:
Catalytic hydrogenation of CO2 to methanol has attracted considerable attention due to its potential in alleviating global warming and mitigating the dependence on fossil fuels. Cu-based catalysts are widely used in industry because of their high activity for methanol production. However, the reaction still suffers from low methanol selectivity because of the generation of CO as a by-product via the reverse water gas shift reaction (RWGS). The formation of another by-product H2O leads to inevitable Cu sintering, which decreases the methanol production rate. It is well known that CO can alter competitive molecular adsorption on the surface and the redox behavior of the active sites; hence, CO doping in feed gas might not only inhibit the RWGS but also minimize surface poisoning by the adsorbed oxygen. On the other hand, CO2 hydrogenation to methanol over Cu-based catalysts is a structure-sensitive reaction, and a change in the precursor can have a remarkable influence on the structure and morphology of the catalyst, and ultimately, the catalytic performance. In this work, Cu/ZnO/Al2O3 catalysts have been prepared via a hydrotalcite-like precursor (CHT-CZA) and a complex phase precursor (CNP-CZA) using co-precipitation and ammonia evaporation methods. Subsequently, the performance of the two types of catalysts with different CO contents (CO2: CO:H2:N2 = x:(24.5 - x):72.5:3) is compared at 250 ℃ and 5 MPa in order to explore the role of CO. The evaluation results show that both catalysts follow a similar trend in the conversion of CO and CO2 as well as the space-time-yield (STY) of MeOH and H2O. The conversions of CO2 and STYH2O decrease gradually with an increase in the CO volume, but STYMeOH is positively correlated with the CO volume. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis reveals that the amount of reduced Cu species on the surface increases with increasing CO content. Judging from these results, the introduction of CO inhibits the RWGS and enhances the methanol yield for both catalysts by removing the surface oxygen as the reducing agent and thereby facilitating the exposure of the active reduced Cu species. On the other hand, transmission electron microscopy (TEM) observations indicate the doped CO may cause agglomeration of particles due to over-reduction, leading to gradual catalyst deactivation. Compared with the traditional CNP-CZA, the catalyst derived from hydrotalcite-like compounds exhibits better activity and long-term stability under all atmospheres, at different CO doping levels. This is because the hydrotalcite-like layer structure helps maintain the active metal state and confine the structure by limiting the agglomeration of Cu species. ![]()
Catalytic hydrogenation of CO2 to methanol has attracted considerable attention due to its potential in alleviating global warming and mitigating the dependence on fossil fuels. Cu-based catalysts are widely used in industry because of their high activity for methanol production. However, the reaction still suffers from low methanol selectivity because of the generation of CO as a by-product via the reverse water gas shift reaction (RWGS). The formation of another by-product H2O leads to inevitable Cu sintering, which decreases the methanol production rate. It is well known that CO can alter competitive molecular adsorption on the surface and the redox behavior of the active sites; hence, CO doping in feed gas might not only inhibit the RWGS but also minimize surface poisoning by the adsorbed oxygen. On the other hand, CO2 hydrogenation to methanol over Cu-based catalysts is a structure-sensitive reaction, and a change in the precursor can have a remarkable influence on the structure and morphology of the catalyst, and ultimately, the catalytic performance. In this work, Cu/ZnO/Al2O3 catalysts have been prepared via a hydrotalcite-like precursor (CHT-CZA) and a complex phase precursor (CNP-CZA) using co-precipitation and ammonia evaporation methods. Subsequently, the performance of the two types of catalysts with different CO contents (CO2: CO:H2:N2 = x:(24.5 - x):72.5:3) is compared at 250 ℃ and 5 MPa in order to explore the role of CO. The evaluation results show that both catalysts follow a similar trend in the conversion of CO and CO2 as well as the space-time-yield (STY) of MeOH and H2O. The conversions of CO2 and STYH2O decrease gradually with an increase in the CO volume, but STYMeOH is positively correlated with the CO volume. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis reveals that the amount of reduced Cu species on the surface increases with increasing CO content. Judging from these results, the introduction of CO inhibits the RWGS and enhances the methanol yield for both catalysts by removing the surface oxygen as the reducing agent and thereby facilitating the exposure of the active reduced Cu species. On the other hand, transmission electron microscopy (TEM) observations indicate the doped CO may cause agglomeration of particles due to over-reduction, leading to gradual catalyst deactivation. Compared with the traditional CNP-CZA, the catalyst derived from hydrotalcite-like compounds exhibits better activity and long-term stability under all atmospheres, at different CO doping levels. This is because the hydrotalcite-like layer structure helps maintain the active metal state and confine the structure by limiting the agglomeration of Cu species.
2022, 38(3): 200202
doi: 10.3866/PKU.WHXB202002024
Abstract:
Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM), common incurable diseases caused by protein misfolding, have shown extensive correlation with each other via cross-aggregation between their related pathogenic peptide, amyloid β protein (Aβ) and human islet amyloid polypeptide (hIAPP), respectively. However, little is known about how these two peptides affect the cross-amyloid aggregation process in vivo. To better simulate the intracorporal environment, where different forms of amyloid aggregates co-exist and very few aggregates probably attach to the vessel wall as seeds, herein, we study the seeded-aggregation of Aβ and hIAPP in the presence of homogeneous or heterogeneous seeds, both in solution and on the solid surface, with different monomer and seed concentrations. In this study, Thioflavin T (ThT) fluorescence assay, atomic force microscopy (AFM), and far-UV circular dichroism (CD) were performed to investigate the aggregation process in solution. Moreover, the binding of monomers with seeds on solid surface was detected by quartz crystal microbalance with dissipation (QCM-D). The 3-(4, 5-dime-thylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assays with human neuroblastoma cells (SH-SY5Y) were finally used to test the cytotoxicity caused by the aggregates. Series of analyses confirmed that a small amount of Aβ40 or hIAPP seeds (1/50 of the monomers in solution) significantly changed the aggregation pathway, forming heterogeneous aggregates with different morphologies and increased β-sheet structures. MTT result showed that the heterogeneous aggregates obtained with Aβ40 and hIAPP seeding reduced the cell viability to 70.5% and 74.4%, respectively, both causing higher cytotoxicity than homogeneous aggregates (82.9% and 76.5%, respectively). The results in solution and on the solid surface both prove that Aβ40 and hIAPP seeds can not only induce rapid aggregation of their homogeneous monomers but also promote the heterogeneous monomers to aggregate, but monomer-heterogeneous seed binding efficiency is lower than that between homogeneous species. The differences in seeding and cross-seeding ability of Aβ40 and hIAPP indicate the barriers depended on the sequence similarity and structural compatibility between different amyloid aggregates. In the case of heterogeneous aggregation, aggregation features largely depend on the seeds. Furthermore, hIAPP seeds exhibited higher cross-seeding efficiency than Aβ40 seeds on the solid surface, which is different from the result in solution where Aβ40 seeds indicating the influence of interfacial properties on aggregation process. This finding would give a deep understanding of the cross-seeding aggregation process and we hope that this work will stimulate more research to explore all possible fundamental and practical aspects of amyloid cross-seeding. ![]()
Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM), common incurable diseases caused by protein misfolding, have shown extensive correlation with each other via cross-aggregation between their related pathogenic peptide, amyloid β protein (Aβ) and human islet amyloid polypeptide (hIAPP), respectively. However, little is known about how these two peptides affect the cross-amyloid aggregation process in vivo. To better simulate the intracorporal environment, where different forms of amyloid aggregates co-exist and very few aggregates probably attach to the vessel wall as seeds, herein, we study the seeded-aggregation of Aβ and hIAPP in the presence of homogeneous or heterogeneous seeds, both in solution and on the solid surface, with different monomer and seed concentrations. In this study, Thioflavin T (ThT) fluorescence assay, atomic force microscopy (AFM), and far-UV circular dichroism (CD) were performed to investigate the aggregation process in solution. Moreover, the binding of monomers with seeds on solid surface was detected by quartz crystal microbalance with dissipation (QCM-D). The 3-(4, 5-dime-thylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assays with human neuroblastoma cells (SH-SY5Y) were finally used to test the cytotoxicity caused by the aggregates. Series of analyses confirmed that a small amount of Aβ40 or hIAPP seeds (1/50 of the monomers in solution) significantly changed the aggregation pathway, forming heterogeneous aggregates with different morphologies and increased β-sheet structures. MTT result showed that the heterogeneous aggregates obtained with Aβ40 and hIAPP seeding reduced the cell viability to 70.5% and 74.4%, respectively, both causing higher cytotoxicity than homogeneous aggregates (82.9% and 76.5%, respectively). The results in solution and on the solid surface both prove that Aβ40 and hIAPP seeds can not only induce rapid aggregation of their homogeneous monomers but also promote the heterogeneous monomers to aggregate, but monomer-heterogeneous seed binding efficiency is lower than that between homogeneous species. The differences in seeding and cross-seeding ability of Aβ40 and hIAPP indicate the barriers depended on the sequence similarity and structural compatibility between different amyloid aggregates. In the case of heterogeneous aggregation, aggregation features largely depend on the seeds. Furthermore, hIAPP seeds exhibited higher cross-seeding efficiency than Aβ40 seeds on the solid surface, which is different from the result in solution where Aβ40 seeds indicating the influence of interfacial properties on aggregation process. This finding would give a deep understanding of the cross-seeding aggregation process and we hope that this work will stimulate more research to explore all possible fundamental and practical aspects of amyloid cross-seeding.
2022, 38(3): 200302
doi: 10.3866/PKU.WHXB202003022
Abstract:
Perovskite solar cells (PSCs) attract much attention for their high efficiency and low processing cost. Power conversion efficiencies (PCEs) higher than 25% have been reported in literature, demonstrating the excellent application prospect of PSCs. In general, the crystallinity and the film composition of perovskite thin films are significant factors in determining device performance. Much effort has been made to control the growth process of perovskite films through the use of additives, passivation layers, special atmosphere treatments, precursor regulation etc. Among these methods, precursor solvent engineering is a simple and direct way to control the perovskite quality, but the controllability of components through solvent engineering is still difficult and has not yet been reported. Herein, we report the controlled formation of PbI2 and PbI2 with dimethyl sulfoxide (DMSO) nano domains through precursor solvent engineering. In particular, tuning the solvent content of the dimethyl sulfoxide: 1, 4-butyrolactone: N, N-dimethylformamide (DMSO : GBL : DMF) in the perovskite precursor solution, controlled the content of PbI2 and PbI2(DMSO) domains. Due to the lower boiling point and weaker coordination of DMF relative to DMSO, part of methylammonium iodide (MAI) would escape from the wet films during the evaporation process. Therefore, the PbI2(DMSO) can't completely convert to perovskite crystals and is retained in the final films as residual PbI2(DMSO) domains. Both UV-vis absorption spectrum and XRD spectrum confirmed the existence of PbI2 and PbI2(DMSO) domains. Importantly, the content of PbI2(DMSO) was controllable by simply changing the relative proportion of DMF. With an increase in the DMF content, the residual PbI2(DMSO) domains gradually increase. In addition, the influence of PbI2 and PbI2(DMSO) domains on the device performance was systematically investigated. The formation of PbI2(DMSO) domains caused a decrease in external quantum efficiency (EQE) of the device over 300–425 nm, and consequently decreased the device performance. That was because the PbI2(DMSO) domain has strong absorption over 300–425 nm. Therefore, the PbI2(DMSO) domains would absorb the photons over 300–425 nm prior to the perovskite, however the photons absorbed by the PbI2(DMSO) domains are not converted into the photocurrent. Thus, the perovskite solar cell containing PbI2(DMSO) showed an EQE loss over 300–425 nm in the EQE spectra. This work provides a simple method to control the components, especially the content of the PbI2(DMSO) domains, in perovskite films through regulating the precursor solvent. Additionally, this work revealed a PbI2(DMSO) domain related EQE loss phenomenon, highlighting the importance of controlling this component. ![]()
Perovskite solar cells (PSCs) attract much attention for their high efficiency and low processing cost. Power conversion efficiencies (PCEs) higher than 25% have been reported in literature, demonstrating the excellent application prospect of PSCs. In general, the crystallinity and the film composition of perovskite thin films are significant factors in determining device performance. Much effort has been made to control the growth process of perovskite films through the use of additives, passivation layers, special atmosphere treatments, precursor regulation etc. Among these methods, precursor solvent engineering is a simple and direct way to control the perovskite quality, but the controllability of components through solvent engineering is still difficult and has not yet been reported. Herein, we report the controlled formation of PbI2 and PbI2 with dimethyl sulfoxide (DMSO) nano domains through precursor solvent engineering. In particular, tuning the solvent content of the dimethyl sulfoxide: 1, 4-butyrolactone: N, N-dimethylformamide (DMSO : GBL : DMF) in the perovskite precursor solution, controlled the content of PbI2 and PbI2(DMSO) domains. Due to the lower boiling point and weaker coordination of DMF relative to DMSO, part of methylammonium iodide (MAI) would escape from the wet films during the evaporation process. Therefore, the PbI2(DMSO) can't completely convert to perovskite crystals and is retained in the final films as residual PbI2(DMSO) domains. Both UV-vis absorption spectrum and XRD spectrum confirmed the existence of PbI2 and PbI2(DMSO) domains. Importantly, the content of PbI2(DMSO) was controllable by simply changing the relative proportion of DMF. With an increase in the DMF content, the residual PbI2(DMSO) domains gradually increase. In addition, the influence of PbI2 and PbI2(DMSO) domains on the device performance was systematically investigated. The formation of PbI2(DMSO) domains caused a decrease in external quantum efficiency (EQE) of the device over 300–425 nm, and consequently decreased the device performance. That was because the PbI2(DMSO) domain has strong absorption over 300–425 nm. Therefore, the PbI2(DMSO) domains would absorb the photons over 300–425 nm prior to the perovskite, however the photons absorbed by the PbI2(DMSO) domains are not converted into the photocurrent. Thus, the perovskite solar cell containing PbI2(DMSO) showed an EQE loss over 300–425 nm in the EQE spectra. This work provides a simple method to control the components, especially the content of the PbI2(DMSO) domains, in perovskite films through regulating the precursor solvent. Additionally, this work revealed a PbI2(DMSO) domain related EQE loss phenomenon, highlighting the importance of controlling this component.
2022, 38(3): 200303
doi: 10.3866/PKU.WHXB202003035
Abstract:
Since the First Industrial Revolution, traditional fossil energy (coal, petroleum, etc.) has been the most important energy source. However, with social progress and technological development, energy consumption continues to increase. But fossil energy not only has limited reserves, it also causes serious problems (environmental pollution, the greenhouse effect). Therefore, the research and development of clean and sustainable energy are particularly important. One research focus is hydrogen energy. Hydrogen is a promising energy carrier due to its high energy density, clean-burning characteristics, and sustainability. However, the challenges of hydrogen storage and transportation seriously limit its practical application in proton exchange membrane fuel cells. A potential solution is hydrogen storage in the form of a more stable precursor. One such precursor, formic acid, decomposes easily at room temperature in the presence of a catalyst without also producing toxic gases. Effective catalysts for formic acid decomposition (FAD) are key to hydrogen production by this method. In this study, a high-performance palladium (Pd)-based catalyst boosted by thin-layered carbon nitride was prepared for formic acid decomposition. First, trimeric thiocyanate was calcined by a one-step method to obtain carbon nitride (C3N4-S) directly, followed by fabrication of a Pd-based FAD catalyst with C3N4-S as support (Pd/C3N4-S). During the pyrolysis of thiocyanuric acid, the overflow of ―SH in the precursor had a peeling effect, so that the C3N4 formed as a thin, broken layer with a large specific surface area and pore volume. Because of the improved specific surface area and pore volume and the resulting large number of defect attachment sites, the C3N4-S support effectively dispersed Pd nanoparticles. Furthermore, owing to the electron effect between the support and the metal, the Pd2+ content on the catalyst surface could be adjusted effectively. Pd/C3N4-S showed excellent FAD performance. This catalyst decomposed formic acid into CO2 and H2 effectively at 30 ℃. The turnover frequency and mass activity were as high as 2083 h-1 and 19.52 mol·g-1·h-1, respectively. Testing of the gas product by gas chromatography showed that it did not contain CO, indicating that the Pd/C3N4-S catalyst had excellent selectivity. The catalyst also had good stability: its performance decreased by less than 10% after four testing cycles. This study provides a guiding example of development of a formic acid hydrogen production catalyst with high cost performance and a simple preparation method. ![]()
Since the First Industrial Revolution, traditional fossil energy (coal, petroleum, etc.) has been the most important energy source. However, with social progress and technological development, energy consumption continues to increase. But fossil energy not only has limited reserves, it also causes serious problems (environmental pollution, the greenhouse effect). Therefore, the research and development of clean and sustainable energy are particularly important. One research focus is hydrogen energy. Hydrogen is a promising energy carrier due to its high energy density, clean-burning characteristics, and sustainability. However, the challenges of hydrogen storage and transportation seriously limit its practical application in proton exchange membrane fuel cells. A potential solution is hydrogen storage in the form of a more stable precursor. One such precursor, formic acid, decomposes easily at room temperature in the presence of a catalyst without also producing toxic gases. Effective catalysts for formic acid decomposition (FAD) are key to hydrogen production by this method. In this study, a high-performance palladium (Pd)-based catalyst boosted by thin-layered carbon nitride was prepared for formic acid decomposition. First, trimeric thiocyanate was calcined by a one-step method to obtain carbon nitride (C3N4-S) directly, followed by fabrication of a Pd-based FAD catalyst with C3N4-S as support (Pd/C3N4-S). During the pyrolysis of thiocyanuric acid, the overflow of ―SH in the precursor had a peeling effect, so that the C3N4 formed as a thin, broken layer with a large specific surface area and pore volume. Because of the improved specific surface area and pore volume and the resulting large number of defect attachment sites, the C3N4-S support effectively dispersed Pd nanoparticles. Furthermore, owing to the electron effect between the support and the metal, the Pd2+ content on the catalyst surface could be adjusted effectively. Pd/C3N4-S showed excellent FAD performance. This catalyst decomposed formic acid into CO2 and H2 effectively at 30 ℃. The turnover frequency and mass activity were as high as 2083 h-1 and 19.52 mol·g-1·h-1, respectively. Testing of the gas product by gas chromatography showed that it did not contain CO, indicating that the Pd/C3N4-S catalyst had excellent selectivity. The catalyst also had good stability: its performance decreased by less than 10% after four testing cycles. This study provides a guiding example of development of a formic acid hydrogen production catalyst with high cost performance and a simple preparation method.
2022, 38(3): 201208
doi: 10.3866/PKU.WHXB202012086
Abstract:
2022, 38(3): 210103
doi: 10.3866/PKU.WHXB202101039
Abstract:
