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2021 Volume 37 Issue 3
2021, 37(3): 190603
doi: 10.3866/PKU.WHXB201906033
Abstract:
Photocathodic protection by TiO2 semiconductor materials for metals has interested many corrosion researchers for years. However, a pure TiO2 semiconductor anode can only absorb ultraviolet light and cannot maintain the photocathodic protection in the dark. This has limited its practical applications to a great extent. Overcoming these limitations is significant as well as challenging. Therefore, the objective of this work is to prepare a modified TiO2 composite film with visible light absorption and charge storage capabilities for application in photocathodic protection. First, we fabricated an ordered TiO2 nanotube array film on a Ti substrate by electrochemical anodization. Then, we prepared NiO nanoparticles on the film via a hydrothermal reaction to obtain a p-n heterostructured NiO/TiO2 nanotube array composite film. The properties of the prepared films were investigated by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-Vis absorption spectroscopy, photoluminescence spectroscopy, and photoelectrochemical techniques. The results indicated that the electrochemically anodized TiO2 film had an anatase phase structure and consisted of vertically ordered nanotubes with an inner diameter of about 80 nm and length of 250 nm. After the NiO nanoparticles were deposited on the film, the TiO2 nanotube array structure remained intact. The main phase of TiO2 was still anatase, but the light absorption of the NiO/TiO2 composite film was extended into the visible region, which was in contrast to that of the simple TiO2 film. Moreover, the composite film showed lower photoluminescence intensities than the TiO2 film, implying that a higher charge carrier separation efficiency could be achieved by modification with NiO. Under white light illumination, the photocurrent density of the NiO/TiO2 composite film in a mixed solution of 0.5 mol·L-1 KOH and 1 mol·L-1 CH3OH reached 176 μA·cm-2, which was 2 times higher than that of the simple TiO2 nanotube film, indicating that the composite film had improved photoelectric conversion efficiency and photoelectrochemical properties. The potential of 403 stainless steel (403SS) in 0.5 mol·L-1 NaCl solution decreased by 380 and 440 mV relative to its corrosion potential when coupled to the TiO2 film and NiO/TiO2 composite film, respectively, under white light illumination. This indicated that the heterostructured NiO/TiO2 film as a photoanode could produce more effective photocathodic protection on the steel as compared with the pure TiO2 film. Even after 2.5 h of illumination, the composite film could continuously provide photocathodic protection to 403SS for about 15.5 h in the dark, suggesting that the NiO/TiO2 composite film had a charge storage capability that was significant for its practical applications. ![]()
Photocathodic protection by TiO2 semiconductor materials for metals has interested many corrosion researchers for years. However, a pure TiO2 semiconductor anode can only absorb ultraviolet light and cannot maintain the photocathodic protection in the dark. This has limited its practical applications to a great extent. Overcoming these limitations is significant as well as challenging. Therefore, the objective of this work is to prepare a modified TiO2 composite film with visible light absorption and charge storage capabilities for application in photocathodic protection. First, we fabricated an ordered TiO2 nanotube array film on a Ti substrate by electrochemical anodization. Then, we prepared NiO nanoparticles on the film via a hydrothermal reaction to obtain a p-n heterostructured NiO/TiO2 nanotube array composite film. The properties of the prepared films were investigated by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-Vis absorption spectroscopy, photoluminescence spectroscopy, and photoelectrochemical techniques. The results indicated that the electrochemically anodized TiO2 film had an anatase phase structure and consisted of vertically ordered nanotubes with an inner diameter of about 80 nm and length of 250 nm. After the NiO nanoparticles were deposited on the film, the TiO2 nanotube array structure remained intact. The main phase of TiO2 was still anatase, but the light absorption of the NiO/TiO2 composite film was extended into the visible region, which was in contrast to that of the simple TiO2 film. Moreover, the composite film showed lower photoluminescence intensities than the TiO2 film, implying that a higher charge carrier separation efficiency could be achieved by modification with NiO. Under white light illumination, the photocurrent density of the NiO/TiO2 composite film in a mixed solution of 0.5 mol·L-1 KOH and 1 mol·L-1 CH3OH reached 176 μA·cm-2, which was 2 times higher than that of the simple TiO2 nanotube film, indicating that the composite film had improved photoelectric conversion efficiency and photoelectrochemical properties. The potential of 403 stainless steel (403SS) in 0.5 mol·L-1 NaCl solution decreased by 380 and 440 mV relative to its corrosion potential when coupled to the TiO2 film and NiO/TiO2 composite film, respectively, under white light illumination. This indicated that the heterostructured NiO/TiO2 film as a photoanode could produce more effective photocathodic protection on the steel as compared with the pure TiO2 film. Even after 2.5 h of illumination, the composite film could continuously provide photocathodic protection to 403SS for about 15.5 h in the dark, suggesting that the NiO/TiO2 composite film had a charge storage capability that was significant for its practical applications.
2021, 37(3): 190704
doi: 10.3866/PKU.WHXB201907049
Abstract:
Aqueous sodium ion batteries (ASIBs) have attracted considerable attention for large-scale energy storage because of their prominent advantages of low cost, high safety, and environment-friendliness. Among the reported cathode materials for ASIBs, Na0.44MnO2 exhibits outstanding structural and hydrochemical stability, and hence is of much interest to research scholars. However, the reversible capacity of Na0.44MnO2 in most of the reported ASIBs was only 40 mAh·g-1 due to the restriction of stable working windows, although the in spite of theoretical capacity is121 mAh·g-1. Recently, we reported a Zn/Na0.44MnO2 dual-ion battery (AZMDIB) based on a Na0.44MnO2 positive electrode, Zn negative electrode, and 6 molL-1 NaOH electrolyte. The alkaline solution lowered the proton insertion potential and expanded the stable working window of the Na0.44MnO2 electrode, thus enhancing the reversible capacity to 80 mAh·g-1. Previous studies have demonstrated that the composition, concentration, and pH of the electrolytes have significant effects on the stable electrochemical window, rate performance, cycling performance, and other electrochemical properties of aqueous batteries. In addition, it has been reported that the co-intercalation of hydrogen ions can be inhibited by increasing the pH of the electrolyte in order to improve the cyclic stability of the electrode. Therefore, exploring the effect of electrolyte concentration and pH on the electrochemical performance of Na0.44MnO2 can provide insight into the design and optimization of high-performance Zn/Na0.44MnO2 aqueous batteries. Hence, in this work, rod-like Na0.44MnO2 was synthesized by ball milling and subsequent high-temperature calcination, and the influence of NaOH concentration on the electrochemical performance of the Na0.44MnO2 electrode was investigated by adopting five different concentrated electrolytes, 1, 3, 6, 8, and 10 mol·L-1 NaOH. The results showed that an increase in NaOH concentration is beneficial for preventing the insertion of protons and improving the cycling performance and the rate performance of the electrode; however, it also leads to premature triggering of the oxygen evolution reaction. Moreover, the rate performance would decrease at high NaOH concentration. The Na0.44MnO2 electrode showed optimal electrochemical performance in 8 mol·L-1 NaOH. At a current density of 0.5C (1C = 121 mA·g-1), a reversible specific capacity of 79.2 mAh·g-1 was obtained, and a capacity of 35.3 mAh·g-1 was maintained even at a high current density of 50C. In the potential window of 0.2–1.2 V (vs. NHE), the capacity retention after 500 weeks was 64.3%, which increased to 78.2% when the potential window was reduced to 0.25–1.15 V, because of the fewer side reactions. In addition, Na0.44MnO2 showed an exceptional ability to sustain overcharging up to 30% in a concentrated alkaline electrolyte (based on the reversible capacity of 79.2 mAh·g-1), and the discharge capacity within 80 cycles was almost steady. The above mentioned results form the basis for possible technical directions toward the development of low-cost cathode materials to be used in ASIBs. ![]()
Aqueous sodium ion batteries (ASIBs) have attracted considerable attention for large-scale energy storage because of their prominent advantages of low cost, high safety, and environment-friendliness. Among the reported cathode materials for ASIBs, Na0.44MnO2 exhibits outstanding structural and hydrochemical stability, and hence is of much interest to research scholars. However, the reversible capacity of Na0.44MnO2 in most of the reported ASIBs was only 40 mAh·g-1 due to the restriction of stable working windows, although the in spite of theoretical capacity is121 mAh·g-1. Recently, we reported a Zn/Na0.44MnO2 dual-ion battery (AZMDIB) based on a Na0.44MnO2 positive electrode, Zn negative electrode, and 6 molL-1 NaOH electrolyte. The alkaline solution lowered the proton insertion potential and expanded the stable working window of the Na0.44MnO2 electrode, thus enhancing the reversible capacity to 80 mAh·g-1. Previous studies have demonstrated that the composition, concentration, and pH of the electrolytes have significant effects on the stable electrochemical window, rate performance, cycling performance, and other electrochemical properties of aqueous batteries. In addition, it has been reported that the co-intercalation of hydrogen ions can be inhibited by increasing the pH of the electrolyte in order to improve the cyclic stability of the electrode. Therefore, exploring the effect of electrolyte concentration and pH on the electrochemical performance of Na0.44MnO2 can provide insight into the design and optimization of high-performance Zn/Na0.44MnO2 aqueous batteries. Hence, in this work, rod-like Na0.44MnO2 was synthesized by ball milling and subsequent high-temperature calcination, and the influence of NaOH concentration on the electrochemical performance of the Na0.44MnO2 electrode was investigated by adopting five different concentrated electrolytes, 1, 3, 6, 8, and 10 mol·L-1 NaOH. The results showed that an increase in NaOH concentration is beneficial for preventing the insertion of protons and improving the cycling performance and the rate performance of the electrode; however, it also leads to premature triggering of the oxygen evolution reaction. Moreover, the rate performance would decrease at high NaOH concentration. The Na0.44MnO2 electrode showed optimal electrochemical performance in 8 mol·L-1 NaOH. At a current density of 0.5C (1C = 121 mA·g-1), a reversible specific capacity of 79.2 mAh·g-1 was obtained, and a capacity of 35.3 mAh·g-1 was maintained even at a high current density of 50C. In the potential window of 0.2–1.2 V (vs. NHE), the capacity retention after 500 weeks was 64.3%, which increased to 78.2% when the potential window was reduced to 0.25–1.15 V, because of the fewer side reactions. In addition, Na0.44MnO2 showed an exceptional ability to sustain overcharging up to 30% in a concentrated alkaline electrolyte (based on the reversible capacity of 79.2 mAh·g-1), and the discharge capacity within 80 cycles was almost steady. The above mentioned results form the basis for possible technical directions toward the development of low-cost cathode materials to be used in ASIBs.
2021, 37(3): 191205
doi: 10.3866/PKU.WHXB201912050
Abstract:
The small size (nanoscale) of proteins and their favorable electron transport (ETp) properties make them suitable for various types of bioelectronic devices and offer a solution for miniaturizing these devices to nanoscale dimensions. The performance of protein-based devices is predominantly affected by the ETp property of the proteins, which is largely determined by the band gaps of the proteins, i.e., the energy difference between the conduction band (CB) and valence band (VB). Regulating the protein ETp band gaps to appropriate values is experimentally demanding and hence remains a significant challenge. This study reports a facile method for modulating the ETp band gaps of bovine serum albumin (BSA), via its binding with a foreign molecule, hemin. The formation of the hemin-BSA complex was initially confirmed by theoretical simulation (molecular docking) and experimental characterization (fluorescence and absorption spectra), which indicated that the hemin is positioned inside a hydrophobic cavity formed by hydrophobic amino acid residues and near Trp213, at subdomain IIA of BSA, with no significant effects on the structure of BSA. Circular dichroism (CD) spectra indicated that the BSA conformation remains essentially unaltered following the formation of the hemin-BSA complex, as the helicities of the free BSA (non-binding) and the hemin-BSA complex were estimated to be 66% and 65%, respectively. Moreover, this structural conformation remains preserved after the hemin-BSA complex is immobilized on the Au substrate surface. The hemin-BSA complex is immobilized onto the Au substrate surface along a single orientation, via the ―SH group of Cys34 on the protein surface. Atomic force microscopy (AFM) images indicate that hemin-BSA forms a dense layer on the surface of the Au substrate with a lateral size of ~3.2‒3.7 nm, which is equivalent to the actual size of BSA, ~4.0 nm × 4.0 nm × 14.0 nm. The current-voltage (I-V) responses were measured using eutectic gallium-indium (EGaIn) as the top electrode and an Au film as the substrate electrode, revealing that the ETp processes of BSA and hemin-BSA on the Au surface have distinct semiconducting characteristics. The CB and VB were estimated by analysis of the differential conductance spectra, and for the free BSA, they were ~0.75 ± 0.04 and ~ −0.75 ± 0.08 eV, respectively, being equally distributed around the Fermi level (0 eV), with a band gap of ~1.50 ± 0.05 eV. Following hemin binding, the CB (~0.64 ± 0.06 eV) and VB (~ −0.29 ± 0.07 eV) of the protein were closer to the Fermi level, resulting in a band gap of ~0.93 ± 0.05 eV. These results demonstrated that hemin molecules can effectively regulate ETp characteristics and the transport band gap of BSA. This methodology may provide a general approach for tuning protein ETp band gaps, enabling broad variability by the preselection of binding molecules. The protein and foreign molecule complex may further serve as a suitable material for configuring nanoscale solid-state bioelectronic devices. ![]()
The small size (nanoscale) of proteins and their favorable electron transport (ETp) properties make them suitable for various types of bioelectronic devices and offer a solution for miniaturizing these devices to nanoscale dimensions. The performance of protein-based devices is predominantly affected by the ETp property of the proteins, which is largely determined by the band gaps of the proteins, i.e., the energy difference between the conduction band (CB) and valence band (VB). Regulating the protein ETp band gaps to appropriate values is experimentally demanding and hence remains a significant challenge. This study reports a facile method for modulating the ETp band gaps of bovine serum albumin (BSA), via its binding with a foreign molecule, hemin. The formation of the hemin-BSA complex was initially confirmed by theoretical simulation (molecular docking) and experimental characterization (fluorescence and absorption spectra), which indicated that the hemin is positioned inside a hydrophobic cavity formed by hydrophobic amino acid residues and near Trp213, at subdomain IIA of BSA, with no significant effects on the structure of BSA. Circular dichroism (CD) spectra indicated that the BSA conformation remains essentially unaltered following the formation of the hemin-BSA complex, as the helicities of the free BSA (non-binding) and the hemin-BSA complex were estimated to be 66% and 65%, respectively. Moreover, this structural conformation remains preserved after the hemin-BSA complex is immobilized on the Au substrate surface. The hemin-BSA complex is immobilized onto the Au substrate surface along a single orientation, via the ―SH group of Cys34 on the protein surface. Atomic force microscopy (AFM) images indicate that hemin-BSA forms a dense layer on the surface of the Au substrate with a lateral size of ~3.2‒3.7 nm, which is equivalent to the actual size of BSA, ~4.0 nm × 4.0 nm × 14.0 nm. The current-voltage (I-V) responses were measured using eutectic gallium-indium (EGaIn) as the top electrode and an Au film as the substrate electrode, revealing that the ETp processes of BSA and hemin-BSA on the Au surface have distinct semiconducting characteristics. The CB and VB were estimated by analysis of the differential conductance spectra, and for the free BSA, they were ~0.75 ± 0.04 and ~ −0.75 ± 0.08 eV, respectively, being equally distributed around the Fermi level (0 eV), with a band gap of ~1.50 ± 0.05 eV. Following hemin binding, the CB (~0.64 ± 0.06 eV) and VB (~ −0.29 ± 0.07 eV) of the protein were closer to the Fermi level, resulting in a band gap of ~0.93 ± 0.05 eV. These results demonstrated that hemin molecules can effectively regulate ETp characteristics and the transport band gap of BSA. This methodology may provide a general approach for tuning protein ETp band gaps, enabling broad variability by the preselection of binding molecules. The protein and foreign molecule complex may further serve as a suitable material for configuring nanoscale solid-state bioelectronic devices.
2021, 37(3): 191005
doi: 10.3866/PKU.WHXB201910058
Abstract:
In recent years, there has been an intense effort to develop renewable alternatives to fossil fuels for meeting the ever-increasing global energy need. Molecular dihydrogen (H2) is the ideal energy carrier for the 21st century because it has high energy density and its combustion releases only water, and electrocatalysis is a powerful tool for its wide use. Developing new H2-evolving molecular electrocatalysts with cheap and earth-abundant elements is highly desirable. Among all kinds of H2-generating catalysts, [NiFe]-hydrogenases (H2ases) have the active site featuring a redox-active {Ni(cysteinate)4} center bridged through two of its cysteine residues to a redox-inactive {Fe(CN2)(CO)} moiety. As a class of known natural enzymes, [NiFe]-H2ases are promising candidates because they have inexpensive nickel and/or iron atoms at the active sites and can catalyze the reversible reduction of H+ to H2 with high efficiency comparable to the noble-metal platinum. However, the catalytic behaviors of most artificial H2ases-like active sites are usually inhibited by the existence of a small amount of O2, which strongly limit their practical application. As such, it is attractive to develop new analogues of enzyme active sites to address this issue. On the other hand, [NiFeSe]-H2ases, which are obtained by the introduction of Se into [NiFe]-H2ases, have exceptional properties conducive for H2 production, such as high H2 generation performance, marginal inhibition by H2, and high tolerance to O2. The mechanistic understanding of [NiFeSe]-H2ases function guides the design and synthesis of Se-substituted Ni-based molecular catalysts, and selection of suitable bio-inspired catalysts enables applications in catalysis for hydrogen evolution reaction (HER). In this contribution, six bio-inspired neutral nickel-based complexes (2a–2c, 3a–3b, 4) with diselenolate derivatives and diphosphine ligands have been prepared and structurally characterized. These complexes are important in the function of [NiFeSe]-hydrogenase models toward their application as electrocatalysts for the HER. The substituent effects of diselenolate and diphosphine ligands on the catalytic activities of hydrogen production by these nickel(Ⅱ) complexes are studied experimentally. When using a glassy carbon electrode, all the complexes are efficient electrocatalysts for H2 production with different turnover frequencies (TOFs) of 12182 s-1 (2a), 15385 s-1 (2b), 20359 s-1 (2c), 106 s-1 (3a), 794 s-1 (3b), 13580 s-1 (4). The present results indicate that the nickel(Ⅱ) complex 2c ligated by a 4, 5-dimethyl-1, 2-benzenediselenolate and 1, 1'-bis(diphenylphosphino)ferrocene ligand, shows the highest efficiency, which surpasses the activity of a previously dppf-supported nickel(Ⅱ) 1, 2-benzenediselenolate with a TOF of 7838 s-1. We believe that our results will encourage the development of the design of highly efficient Ni-based selenolate molecular catalysts. ![]()
In recent years, there has been an intense effort to develop renewable alternatives to fossil fuels for meeting the ever-increasing global energy need. Molecular dihydrogen (H2) is the ideal energy carrier for the 21st century because it has high energy density and its combustion releases only water, and electrocatalysis is a powerful tool for its wide use. Developing new H2-evolving molecular electrocatalysts with cheap and earth-abundant elements is highly desirable. Among all kinds of H2-generating catalysts, [NiFe]-hydrogenases (H2ases) have the active site featuring a redox-active {Ni(cysteinate)4} center bridged through two of its cysteine residues to a redox-inactive {Fe(CN2)(CO)} moiety. As a class of known natural enzymes, [NiFe]-H2ases are promising candidates because they have inexpensive nickel and/or iron atoms at the active sites and can catalyze the reversible reduction of H+ to H2 with high efficiency comparable to the noble-metal platinum. However, the catalytic behaviors of most artificial H2ases-like active sites are usually inhibited by the existence of a small amount of O2, which strongly limit their practical application. As such, it is attractive to develop new analogues of enzyme active sites to address this issue. On the other hand, [NiFeSe]-H2ases, which are obtained by the introduction of Se into [NiFe]-H2ases, have exceptional properties conducive for H2 production, such as high H2 generation performance, marginal inhibition by H2, and high tolerance to O2. The mechanistic understanding of [NiFeSe]-H2ases function guides the design and synthesis of Se-substituted Ni-based molecular catalysts, and selection of suitable bio-inspired catalysts enables applications in catalysis for hydrogen evolution reaction (HER). In this contribution, six bio-inspired neutral nickel-based complexes (2a–2c, 3a–3b, 4) with diselenolate derivatives and diphosphine ligands have been prepared and structurally characterized. These complexes are important in the function of [NiFeSe]-hydrogenase models toward their application as electrocatalysts for the HER. The substituent effects of diselenolate and diphosphine ligands on the catalytic activities of hydrogen production by these nickel(Ⅱ) complexes are studied experimentally. When using a glassy carbon electrode, all the complexes are efficient electrocatalysts for H2 production with different turnover frequencies (TOFs) of 12182 s-1 (2a), 15385 s-1 (2b), 20359 s-1 (2c), 106 s-1 (3a), 794 s-1 (3b), 13580 s-1 (4). The present results indicate that the nickel(Ⅱ) complex 2c ligated by a 4, 5-dimethyl-1, 2-benzenediselenolate and 1, 1'-bis(diphenylphosphino)ferrocene ligand, shows the highest efficiency, which surpasses the activity of a previously dppf-supported nickel(Ⅱ) 1, 2-benzenediselenolate with a TOF of 7838 s-1. We believe that our results will encourage the development of the design of highly efficient Ni-based selenolate molecular catalysts.
2021, 37(3): 191101
doi: 10.3866/PKU.WHXB201911011
Abstract:
In recent years, increasing efforts have been undertaken to develop non-precious metal (NPM) catalysts with both high activity and stability toward the oxygen reduction reaction (ORR), since they are much less expensive than commercially available Pt-based electrocatalysts. Transition metal macrocyclic compounds contain transition metal, nitrogen, and carbon species, hence becoming promising precursors for the synthesis of NPM catalysts. Hemin, a natural transition-metal-based macrocyclic compound, is widely applied to the synthesis of NPM electrocatalysts. However, the ORR activity of hemin-derived electrocatalysts must be improved considerably as compared with that of state-of-the-art NPM electrocatalysts. Morphology control is an efficient method to increase the exposure of active sites, thus enhancing the ORR activity. Here, we fabricated a hollow NPM electrocatalyst (hemin hollow derivative, Hemin-HD) using hemin as the precursor and NaCl as the template. First, hemin and NaCl were dispersed and mixed in solution. With an increase in the temperature, the solution was vapored and NaCl began to crystallize. Hemin wrapped the outer surface of NaCl because of the ionic interaction between these two compounds. The as-obtained powders were collected and carbonized at high temperature under a nitrogen atmosphere. Then, the NaCl template was removed by washing, and the hollow material Hemin-HD was obtained. Physicochemical characterization by transmission electron microscopy (TEM), X-ray diffraction (XRD), surface area measurements and X-ray photoelectron spectroscopy (XPS) confirmed that the surface area and pore volume of the as-obtained Hemin-HD electrocatalyst increased by a factor of 6.5 and 3.8, respectively, relative to those of the Hemin-D (hemin derivative) sample without the NaCl template. Owing to the hollow structure and increased surface area, the Fe and N content on the Hemin-HD surface were higher than those on the Hemin-D surface. Consequently, Hemin-HD showed better ORR activity in alkali solution than Hemin-D did, this was confirmed by the fact that the half-wave potential of Hemin-HD was greater than that of Hemin-D by 20 mV, and faster kinetics were observed for the former, as calculated by the Tafel slope. The performance of Hemin-HD was comparable to that of commercial Pt/C catalysts for the ORR in alkali solution. It is believed that the hollow structure allows the dispersion of active sites on both the inner and outer surfaces, thus facilitating the exposure of a great number of active sites. Besides, the pore structure of the electrocatalyst is expected to boost mass transfer and improve the contact between the active sites and reactants, thus enhancing the ORR activity. ![]()
In recent years, increasing efforts have been undertaken to develop non-precious metal (NPM) catalysts with both high activity and stability toward the oxygen reduction reaction (ORR), since they are much less expensive than commercially available Pt-based electrocatalysts. Transition metal macrocyclic compounds contain transition metal, nitrogen, and carbon species, hence becoming promising precursors for the synthesis of NPM catalysts. Hemin, a natural transition-metal-based macrocyclic compound, is widely applied to the synthesis of NPM electrocatalysts. However, the ORR activity of hemin-derived electrocatalysts must be improved considerably as compared with that of state-of-the-art NPM electrocatalysts. Morphology control is an efficient method to increase the exposure of active sites, thus enhancing the ORR activity. Here, we fabricated a hollow NPM electrocatalyst (hemin hollow derivative, Hemin-HD) using hemin as the precursor and NaCl as the template. First, hemin and NaCl were dispersed and mixed in solution. With an increase in the temperature, the solution was vapored and NaCl began to crystallize. Hemin wrapped the outer surface of NaCl because of the ionic interaction between these two compounds. The as-obtained powders were collected and carbonized at high temperature under a nitrogen atmosphere. Then, the NaCl template was removed by washing, and the hollow material Hemin-HD was obtained. Physicochemical characterization by transmission electron microscopy (TEM), X-ray diffraction (XRD), surface area measurements and X-ray photoelectron spectroscopy (XPS) confirmed that the surface area and pore volume of the as-obtained Hemin-HD electrocatalyst increased by a factor of 6.5 and 3.8, respectively, relative to those of the Hemin-D (hemin derivative) sample without the NaCl template. Owing to the hollow structure and increased surface area, the Fe and N content on the Hemin-HD surface were higher than those on the Hemin-D surface. Consequently, Hemin-HD showed better ORR activity in alkali solution than Hemin-D did, this was confirmed by the fact that the half-wave potential of Hemin-HD was greater than that of Hemin-D by 20 mV, and faster kinetics were observed for the former, as calculated by the Tafel slope. The performance of Hemin-HD was comparable to that of commercial Pt/C catalysts for the ORR in alkali solution. It is believed that the hollow structure allows the dispersion of active sites on both the inner and outer surfaces, thus facilitating the exposure of a great number of active sites. Besides, the pore structure of the electrocatalyst is expected to boost mass transfer and improve the contact between the active sites and reactants, thus enhancing the ORR activity.
2021, 37(3): 200506
doi: 10.3866/PKU.WHXB202005062
Abstract:
With the development of electric vehicles (EVs) and hybrid electric vehicles (HEVs), the demand for lithium ion power batteries with high energy density and long cycle life has continuously increased in the recent years. According to the "Made in China 2025" plan, the energy densities of lithium ion batteries need to reach 300 Wh·kg-1 in 2020. Due to their high discharge capacities and work voltages, Ni-rich layered materials have attracted considerable attention from the science and industry fields as one of the most promising cathodes to achieve high energy density. According to previous reports, the discharge capacities of Ni-rich cathodes were positively correlated to their Ni content. However, the increased Ni content can aggravate the side reactions between the cathode and electrolyte, induce O loss, and trigger structural transformation from the surface to bulk. In this study, ZrO2 was coated on LiNi0.8Co0.1Mn0.1O2 with a simple wet chemical method to improve its cycle performance. The scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) demonstrated that Zr was only detected in the ZrO2-coated samples and was mainly distributed at the surface of the secondary particles of the LiNi0.8Co0.1Mn0.1O2 cathodes. The X-ray diffraction (XRD) indicated that Zr4+ in ZrO2 migrated into the layered surface structure of LiNi0.8Co0.1Mn0.1O2 based on the shift of the (003) peak to a lower angle, which was considered as a lattice expansion along the c axis. Under the cut-off voltage of 4.3 and 4.5 V, the capacity retentions of the LiNi0.8Co0.1Mn0.1O2 cathodes improved from 84.89 to 97.61% and 75.60 to 81.37%, respectively, after 100 cycles at 1C. This was mainly attributed to the doped Zr4+ in surface structure as opposed to the ZrO2 coating. The X-ray photoelectron spectroscopy (XPS) indicated that the Ni3+ at the surface of LiNi0.8Co0.1Mn0.1O2 was reduced to Ni2+ after the Zr4+ surface doping due to charge balance. Rietveld refinement also indicated that the Li+/Ni2+ cation disordering improved after the Zr4+ in ZrO2 doped into NCM surface structure. The raised cation disordering may be triggered by the increased content of Ni2+ and their migration into Li layers due to the similar ion radius of Li+ (0.076 nm) and Ni2+ (0.069 nm). A structure-reconstructed layer at the surface of LiNi0.8Co0.1Mn0.1O2 was formed after the Zr4+ doping, which had been confirmed by transmission electron microscope (TEM). It was determined that this structure-reconstructed layer can hinder the side reactions at the interface and stabilize the bulk structure during cycles; thus, the cycle stability of LiNi0.8Co0.1Mn0.1O2 material was improved. ![]()
With the development of electric vehicles (EVs) and hybrid electric vehicles (HEVs), the demand for lithium ion power batteries with high energy density and long cycle life has continuously increased in the recent years. According to the "Made in China 2025" plan, the energy densities of lithium ion batteries need to reach 300 Wh·kg-1 in 2020. Due to their high discharge capacities and work voltages, Ni-rich layered materials have attracted considerable attention from the science and industry fields as one of the most promising cathodes to achieve high energy density. According to previous reports, the discharge capacities of Ni-rich cathodes were positively correlated to their Ni content. However, the increased Ni content can aggravate the side reactions between the cathode and electrolyte, induce O loss, and trigger structural transformation from the surface to bulk. In this study, ZrO2 was coated on LiNi0.8Co0.1Mn0.1O2 with a simple wet chemical method to improve its cycle performance. The scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) demonstrated that Zr was only detected in the ZrO2-coated samples and was mainly distributed at the surface of the secondary particles of the LiNi0.8Co0.1Mn0.1O2 cathodes. The X-ray diffraction (XRD) indicated that Zr4+ in ZrO2 migrated into the layered surface structure of LiNi0.8Co0.1Mn0.1O2 based on the shift of the (003) peak to a lower angle, which was considered as a lattice expansion along the c axis. Under the cut-off voltage of 4.3 and 4.5 V, the capacity retentions of the LiNi0.8Co0.1Mn0.1O2 cathodes improved from 84.89 to 97.61% and 75.60 to 81.37%, respectively, after 100 cycles at 1C. This was mainly attributed to the doped Zr4+ in surface structure as opposed to the ZrO2 coating. The X-ray photoelectron spectroscopy (XPS) indicated that the Ni3+ at the surface of LiNi0.8Co0.1Mn0.1O2 was reduced to Ni2+ after the Zr4+ surface doping due to charge balance. Rietveld refinement also indicated that the Li+/Ni2+ cation disordering improved after the Zr4+ in ZrO2 doped into NCM surface structure. The raised cation disordering may be triggered by the increased content of Ni2+ and their migration into Li layers due to the similar ion radius of Li+ (0.076 nm) and Ni2+ (0.069 nm). A structure-reconstructed layer at the surface of LiNi0.8Co0.1Mn0.1O2 was formed after the Zr4+ doping, which had been confirmed by transmission electron microscope (TEM). It was determined that this structure-reconstructed layer can hinder the side reactions at the interface and stabilize the bulk structure during cycles; thus, the cycle stability of LiNi0.8Co0.1Mn0.1O2 material was improved.
2021, 37(3): 200603
doi: 10.3866/PKU.WHXB202006030
Abstract:
Perovskite solar cells (PSCs) have recently become one of the fastest-growing research fields. Furthermore, the PSCs that have a SnO2 nanoparticle layer as an electron transport layer (ETL) have received extensive attention. The SnO2-ETL layer can be prepared at a low temperature, which makes it suitable for flexible device development. However, the energy levels of the SnO2 layer do not sufficiently match the energy levels of the perovskite light-absorbing layer, which largely affects the charge carrier extraction and reduces the open current–voltage (Voc) of PSCs. Additionally, the interface between the ETL and perovskite layer always has defects, which cause charge recombination and affect the power conversion efficiency (PCE) of PSCs. Therefore, the interfacial engineering at the SnO2/perovskite layer is crucial to address these issues. Researchers are looking for suitable passivation materials that could align the energy band and decrease the defect density. Halide materials, such as KCl and NH4Cl, are promising solutions to solve these problems. However, the preparation process has to be explored, and the mechanism of halide ions at the interface is unclear. This study investigates the effects of SnO2 surface halogenation on the photovoltaic performance of PSCs in depth. The SnO2 surface was passivated using tetrabutylammonium chloride (TBAC), tetrabutylammonium bromide (TBAB), and tetrabutylammonium iodide (TBAI) and the concentration gradient of the passivation solution was studied. Extensive characterization of the perovskite layers and PSC devices demonstrated the positive effects of SnO2 surface halogenation on the SnO2/perovskite interfacial properties. The causes of improved performance of the interfacial-engineered devices were studied using charge carrier dynamics. Interfacial engineering was further investigated by performing first-principles calculations based on density functional theory (DFT) to determine the energy, structure, charge density, density of states, work function, etc. Experiments and theoretical calculations proved that TBAC could be an optimal passivation material for the SnO2 surface. Furthermore, the passivation effect became more apparent with the increase in solution concentration. TBAC could promote perovskite crystal growth, decrease defects at the interface, and increase the internal recombination resistance. Consequently, the photovoltaic performance of PSCs was improved. The halide ions on the SnO2 surface could interact with Sn atoms, which increase the charge density and achieves high-efficiency charge extraction. This work shows the significance of improving the photovoltaic performance of PSCs along with providing physical principles for the interfacial engineering of PSCs toward achieving high efficiency. ![]()
Perovskite solar cells (PSCs) have recently become one of the fastest-growing research fields. Furthermore, the PSCs that have a SnO2 nanoparticle layer as an electron transport layer (ETL) have received extensive attention. The SnO2-ETL layer can be prepared at a low temperature, which makes it suitable for flexible device development. However, the energy levels of the SnO2 layer do not sufficiently match the energy levels of the perovskite light-absorbing layer, which largely affects the charge carrier extraction and reduces the open current–voltage (Voc) of PSCs. Additionally, the interface between the ETL and perovskite layer always has defects, which cause charge recombination and affect the power conversion efficiency (PCE) of PSCs. Therefore, the interfacial engineering at the SnO2/perovskite layer is crucial to address these issues. Researchers are looking for suitable passivation materials that could align the energy band and decrease the defect density. Halide materials, such as KCl and NH4Cl, are promising solutions to solve these problems. However, the preparation process has to be explored, and the mechanism of halide ions at the interface is unclear. This study investigates the effects of SnO2 surface halogenation on the photovoltaic performance of PSCs in depth. The SnO2 surface was passivated using tetrabutylammonium chloride (TBAC), tetrabutylammonium bromide (TBAB), and tetrabutylammonium iodide (TBAI) and the concentration gradient of the passivation solution was studied. Extensive characterization of the perovskite layers and PSC devices demonstrated the positive effects of SnO2 surface halogenation on the SnO2/perovskite interfacial properties. The causes of improved performance of the interfacial-engineered devices were studied using charge carrier dynamics. Interfacial engineering was further investigated by performing first-principles calculations based on density functional theory (DFT) to determine the energy, structure, charge density, density of states, work function, etc. Experiments and theoretical calculations proved that TBAC could be an optimal passivation material for the SnO2 surface. Furthermore, the passivation effect became more apparent with the increase in solution concentration. TBAC could promote perovskite crystal growth, decrease defects at the interface, and increase the internal recombination resistance. Consequently, the photovoltaic performance of PSCs was improved. The halide ions on the SnO2 surface could interact with Sn atoms, which increase the charge density and achieves high-efficiency charge extraction. This work shows the significance of improving the photovoltaic performance of PSCs along with providing physical principles for the interfacial engineering of PSCs toward achieving high efficiency.
2021, 37(3): 200501
doi: 10.3866/PKU.WHXB202005013
Abstract:
In the past few decades, lithium-ion batteries (LIBs) have dominated the market of rechargeable batteries and are extensively applied in the field of electronic devices (e.g., mobile phones and computers). However, lack of lithium resources, high cost of lithium as well as toxic and flammable organic electrolytes significantly hinder further development and large-scale application of LIBs. Therefore, it is necessary to develop next-generation green rechargeable batteries to replace LIBs. Recently, aqueous zinc-ion batteries (AZIBs) have been considered as energy storage devices with substantial development prospects for future large-scale storage systems owing to their high safety performance, low production cost, abundant zinc resources, and environmental friendliness. Typically, we use zinc metal as the anode with neutral or weakly acidic aqueous electrolyte (pH: 3.6–6.0). However, cathode materials have high requirements for AZIBs while considering the charge effect of multivalent metal ions. Currently, one of the research emphases is to develop suitable zinc ion intercalation cathode materials with stable structures and high capacities. Among all types of cathode materials, vanadium-based compounds have the advantages of low cost and high reversible capacity. Additionally, their structure is variable, mainly including layered, tunneled and natrium super ionic conductor (NASICON) structure. Therefore, vanadium-based compounds have clear application possibility in AZIBs. However, there are still several significant problems. In particular, vanadium-based compounds generally have poor conductivity and low voltage platform. Electrochemical performance can be significantly improved mainly by pre-inserting metal ions or water molecules, optimizing the electrolyte, and controlling morphology of nanomaterials (nanosheets, nanospheres, etc.). In addition, the zinc storage mechanism in vanadium-based compounds is more complicated and controversial, including Zn2+ intercalation/deintercalation mechanism, co-insertion mechanism, and conversion reaction mechanism. Moreover, different materials usually exhibit different electrochemical properties and energy storage mechanisms. In this review, we comprehensively describe the energy storage mechanisms of vanadium-based compounds and discuss the application as well as development status of vanadium-based materials in AZIBs. Further, several strategies for improving their performance are proposed, including structural design (e.g., pre-insertion of metal ions or water molecules), morphology control (e.g., carbon coating), and electrolyte optimization (e.g., adjustment of composition and concentration). In particular, pre-insertion of metal ions or water molecules in the original structure can effectively solve these problems of low ion diffusion rate, poor conductivity, and structural instability, thereby achieving excellent electrochemical performance. Moreover, the application of a high-concentration electrolyte is a simple and effective strategy that can not only significantly widen the electrochemical stability window of the aqueous electrolyte but also suppress the dissolution of vanadium, thereby effectively improving energy density and cycling stability for AZIBs. Accordingly, the future development direction of AZIBs and their vanadium-based cathode materials is further prospected, aiming at designing high-performance electrode materials for AZIBs. ![]()
In the past few decades, lithium-ion batteries (LIBs) have dominated the market of rechargeable batteries and are extensively applied in the field of electronic devices (e.g., mobile phones and computers). However, lack of lithium resources, high cost of lithium as well as toxic and flammable organic electrolytes significantly hinder further development and large-scale application of LIBs. Therefore, it is necessary to develop next-generation green rechargeable batteries to replace LIBs. Recently, aqueous zinc-ion batteries (AZIBs) have been considered as energy storage devices with substantial development prospects for future large-scale storage systems owing to their high safety performance, low production cost, abundant zinc resources, and environmental friendliness. Typically, we use zinc metal as the anode with neutral or weakly acidic aqueous electrolyte (pH: 3.6–6.0). However, cathode materials have high requirements for AZIBs while considering the charge effect of multivalent metal ions. Currently, one of the research emphases is to develop suitable zinc ion intercalation cathode materials with stable structures and high capacities. Among all types of cathode materials, vanadium-based compounds have the advantages of low cost and high reversible capacity. Additionally, their structure is variable, mainly including layered, tunneled and natrium super ionic conductor (NASICON) structure. Therefore, vanadium-based compounds have clear application possibility in AZIBs. However, there are still several significant problems. In particular, vanadium-based compounds generally have poor conductivity and low voltage platform. Electrochemical performance can be significantly improved mainly by pre-inserting metal ions or water molecules, optimizing the electrolyte, and controlling morphology of nanomaterials (nanosheets, nanospheres, etc.). In addition, the zinc storage mechanism in vanadium-based compounds is more complicated and controversial, including Zn2+ intercalation/deintercalation mechanism, co-insertion mechanism, and conversion reaction mechanism. Moreover, different materials usually exhibit different electrochemical properties and energy storage mechanisms. In this review, we comprehensively describe the energy storage mechanisms of vanadium-based compounds and discuss the application as well as development status of vanadium-based materials in AZIBs. Further, several strategies for improving their performance are proposed, including structural design (e.g., pre-insertion of metal ions or water molecules), morphology control (e.g., carbon coating), and electrolyte optimization (e.g., adjustment of composition and concentration). In particular, pre-insertion of metal ions or water molecules in the original structure can effectively solve these problems of low ion diffusion rate, poor conductivity, and structural instability, thereby achieving excellent electrochemical performance. Moreover, the application of a high-concentration electrolyte is a simple and effective strategy that can not only significantly widen the electrochemical stability window of the aqueous electrolyte but also suppress the dissolution of vanadium, thereby effectively improving energy density and cycling stability for AZIBs. Accordingly, the future development direction of AZIBs and their vanadium-based cathode materials is further prospected, aiming at designing high-performance electrode materials for AZIBs.
2021, 37(3): 200502
doi: 10.3866/PKU.WHXB202005020
Abstract:
The growing demand for electric vehicles, communication devices, and grid-scale energy storage systems urgently calls for the development of rechargeable batteries. Although lithium-ion batteries have dominated the new energy market for decades, there are challenges limiting their development, such as the high cost of lithium, as well as the toxicity and flammability of the organic electrolyte. In recent years, aqueous zinc-ion batteries (ZIBs) have gained much attention due to their advantages of high safety, high capacity, low cost, and nontoxicity. Materials based on multivalent vanadium and manganese have shown great potential for application as cathodes that are compatible with the metallic zinc anode in ZIBs. However, the commercialization of ZIBs has been hindered by the choice of cathodes, since the cathode materials show unsatisfactory energy densities and suffer from severe structural collapse, dissolution of the electrode components, sluggish reaction kinetics and detrimental side reactions during cycling. This stalemate was broken when a Zn2+/H2O co-inserted V2O5 (Zn0.25V2O5·nH2O) material was first reported in 2016, and it showed much higher cycling stability and capacity than those of V2O5. The Zn2+ and water molecules pre-intercalated into the interlayer served as pillars to maintain the crystal structure and increase the interplanar spacing, leading to high structural stability and fast Zn2+ diffusion. Since then, several guest ions (Li+, Na+, K+, Ca2+, NH4+, PO43-, N3-, etc.) and molecules (H2O, polyethylene dioxythiophene (PEDOT), polyaniline (PANI, etc.) have been widely used to improve the electrochemical performance of aqueous ZIB cathodes, especially with manganese-based and vanadium-based materials. It is demonstrated that pre-intercalation of the guest ions or molecules can effectively optimize the electronic structure, regulate the interplanar spacing, and improve the reaction kinetics of the host. The local coordination structure of the host with pre-intercalated guest ions/molecules directly influences the zinc-ion storage performance. For example, sodium vanadates with a tunneled structure generally show better cycling stability than those with a layered structure due to their stronger Na-O bonds, since the O atoms on their layer surfaces are only single-connected. Manganese dissolution could be greatly suppressed by intercalation of the large potassium ions into tunneled α-MnO2, where solid K-O bonds act as pillars to be connected with Mn polyhedrons, and thus strengthen the structure. New mechanisms underlying reduction/displacement reactions could also be revealed in vanadates upon the introduction of Ag+ and Cu2+. Thus, we believe that guest pre-intercalation is a promising method for optimizing the zinc-ion storage performance of the appropriate cathodes and is worthy for further exploration. Here we have reviewed the recent advances in manganese-based and vanadium-based cathodes via the guest pre-intercalation strategy, discussed the related advantages and challenges. The future research direction for these two kinds of aqueous ZIB cathodes is also prospected. ![]()
The growing demand for electric vehicles, communication devices, and grid-scale energy storage systems urgently calls for the development of rechargeable batteries. Although lithium-ion batteries have dominated the new energy market for decades, there are challenges limiting their development, such as the high cost of lithium, as well as the toxicity and flammability of the organic electrolyte. In recent years, aqueous zinc-ion batteries (ZIBs) have gained much attention due to their advantages of high safety, high capacity, low cost, and nontoxicity. Materials based on multivalent vanadium and manganese have shown great potential for application as cathodes that are compatible with the metallic zinc anode in ZIBs. However, the commercialization of ZIBs has been hindered by the choice of cathodes, since the cathode materials show unsatisfactory energy densities and suffer from severe structural collapse, dissolution of the electrode components, sluggish reaction kinetics and detrimental side reactions during cycling. This stalemate was broken when a Zn2+/H2O co-inserted V2O5 (Zn0.25V2O5·nH2O) material was first reported in 2016, and it showed much higher cycling stability and capacity than those of V2O5. The Zn2+ and water molecules pre-intercalated into the interlayer served as pillars to maintain the crystal structure and increase the interplanar spacing, leading to high structural stability and fast Zn2+ diffusion. Since then, several guest ions (Li+, Na+, K+, Ca2+, NH4+, PO43-, N3-, etc.) and molecules (H2O, polyethylene dioxythiophene (PEDOT), polyaniline (PANI, etc.) have been widely used to improve the electrochemical performance of aqueous ZIB cathodes, especially with manganese-based and vanadium-based materials. It is demonstrated that pre-intercalation of the guest ions or molecules can effectively optimize the electronic structure, regulate the interplanar spacing, and improve the reaction kinetics of the host. The local coordination structure of the host with pre-intercalated guest ions/molecules directly influences the zinc-ion storage performance. For example, sodium vanadates with a tunneled structure generally show better cycling stability than those with a layered structure due to their stronger Na-O bonds, since the O atoms on their layer surfaces are only single-connected. Manganese dissolution could be greatly suppressed by intercalation of the large potassium ions into tunneled α-MnO2, where solid K-O bonds act as pillars to be connected with Mn polyhedrons, and thus strengthen the structure. New mechanisms underlying reduction/displacement reactions could also be revealed in vanadates upon the introduction of Ag+ and Cu2+. Thus, we believe that guest pre-intercalation is a promising method for optimizing the zinc-ion storage performance of the appropriate cathodes and is worthy for further exploration. Here we have reviewed the recent advances in manganese-based and vanadium-based cathodes via the guest pre-intercalation strategy, discussed the related advantages and challenges. The future research direction for these two kinds of aqueous ZIB cathodes is also prospected.
2021, 37(3): 200905
doi: 10.3866/PKU.WHXB202009056
Abstract:
Semitransparent organic solar cells (ST-OSCs) have attracted attention for use in building integrated photovoltaics because of their large range tunability in colors, transparency, and high efficiency. However, the development of semitransparent devices based on fullerene acceptors remained almost stagnant in the early period. This was due to the weak absorption of fullerene small molecules in the visible and near-infrared regions as well as the large non-radiative energy loss, resulting in drastic open-circuit voltage loss. In addition, the energy level and chemical structure of fullerene molecules cannot be easily regulated, and the strong aggregation characteristics of fullerenes greatly limit the development of OSCs. In contrast, the designability of the chemical structures and controllability of the energy levels of non-fullerene electron acceptors has encouraged researchers to explore high-performance organic solar cells while and simultaneously stimulating the development of ST-OSCs. In this review, the recent progress in non-fullerene small molecule acceptors for ST-OSCs is summarized. The article focuses on ST-OSCs from the aspects of device structures and active layers. In view of the semitransparent device structure, except for replacing the traditional electrodes with semitransparent electrodes, researchers have introduced suitable interface layers to regulate the absorption and reflection of sunlight. The interface layers mainly contain a reflective layer (evaporated on the top electrode to reflect near-infrared light); an anti-reflection layer (located below ITO (indium tin oxide)) to mitigate light reflection at the air-glass interface and thus enhance the absorption of sunlight); and an optical outcoupling layer (simultaneously increasing reflection and transmission). From the active layer, it is mainly divided into two categories. First, researchers have optimized the photovoltaic performance of semitransparent devices from the perspective of molecular structures, mainly by broadening the absorption window of non-fullerene small molecule acceptors, thus improving the crystallinity and charge mobility of small molecules, and regulating the stacking behavior and orientation of molecules in the films. Second, regarding the active layer processing, much effort has been undertaken to optimize the light absorption, morphology, and charge carrier transport channels of blended films. ![]()
Semitransparent organic solar cells (ST-OSCs) have attracted attention for use in building integrated photovoltaics because of their large range tunability in colors, transparency, and high efficiency. However, the development of semitransparent devices based on fullerene acceptors remained almost stagnant in the early period. This was due to the weak absorption of fullerene small molecules in the visible and near-infrared regions as well as the large non-radiative energy loss, resulting in drastic open-circuit voltage loss. In addition, the energy level and chemical structure of fullerene molecules cannot be easily regulated, and the strong aggregation characteristics of fullerenes greatly limit the development of OSCs. In contrast, the designability of the chemical structures and controllability of the energy levels of non-fullerene electron acceptors has encouraged researchers to explore high-performance organic solar cells while and simultaneously stimulating the development of ST-OSCs. In this review, the recent progress in non-fullerene small molecule acceptors for ST-OSCs is summarized. The article focuses on ST-OSCs from the aspects of device structures and active layers. In view of the semitransparent device structure, except for replacing the traditional electrodes with semitransparent electrodes, researchers have introduced suitable interface layers to regulate the absorption and reflection of sunlight. The interface layers mainly contain a reflective layer (evaporated on the top electrode to reflect near-infrared light); an anti-reflection layer (located below ITO (indium tin oxide)) to mitigate light reflection at the air-glass interface and thus enhance the absorption of sunlight); and an optical outcoupling layer (simultaneously increasing reflection and transmission). From the active layer, it is mainly divided into two categories. First, researchers have optimized the photovoltaic performance of semitransparent devices from the perspective of molecular structures, mainly by broadening the absorption window of non-fullerene small molecule acceptors, thus improving the crystallinity and charge mobility of small molecules, and regulating the stacking behavior and orientation of molecules in the films. Second, regarding the active layer processing, much effort has been undertaken to optimize the light absorption, morphology, and charge carrier transport channels of blended films.
2021, 37(3): 200705
doi: 10.3866/PKU.WHXB202007055
Abstract:
2021, 37(3): 200801
doi: 10.3866/PKU.WHXB202008016
Abstract:
2021, 37(3): 200805
doi: 10.3866/PKU.WHXB202008059
Abstract:
2021, 37(3): 201004
doi: 10.3866/PKU.WHXB202010046
Abstract:
2021, 37(3): 201006
doi: 10.3866/PKU.WHXB202010065
Abstract:
