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2020 Volume 36 Issue 7
2020, 36(7): 190304
doi: 10.3866/PKU.WHXB201903046
Abstract:
The looming global energy crisis and ever-increasing energy demands have catalyzed the development of renewable energy storage systems. In this regard, supercapacitors (SCs) have attracted widespread attention because of their advantageous attributes such as high power density, excellent cycle stability, and environmental friendliness. However, SCs exhibit low energy density and it is important to optimize electrode materials to improve the overall performance of these devices. Among the various electrode materials available, spinel nickel cobaltate (NiCo2O4) is particularly interesting because of its excellent theoretical capacitance. Based on the understanding that the performances of the electrode materials strongly depend on their morphologies and structures, in this study, we successfully synthesized NiCo2O4 nanosheets on Ni foam via a simple hydrothermal route followed by calcination. The structures and morphologies of the as-synthesized products were characterized by X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller (BET) surface area analysis, and the results showed that they were uniformly distributed on the Ni foam support. The surface chemical states of the elements in the samples were identified by X-ray photoelectron spectroscopy. The as-synthesized NiCo2O4 products were then tested as cathode materials for supercapacitors in a traditional three-electrode system. The electrochemical performances of the NiCo2O4 electrode materials were studied and the area capacitance was found to be 1.26 C∙cm-2 at a current density of 1 mA∙cm-2. Furthermore, outstanding cycling stability with 97.6% retention of the initial discharge capacitance after 10000 cycles and excellent rate performance (67.5% capacitance retention with the current density from 1 to 14 mA∙cm-2) were achieved. It was found that the Ni foam supporting the NiCo2O4 nanosheets increased the conductivity of the electrode materials. However, it is worth noting that the contribution of nickel foam to the areal capacitance of the electrode materials was almost zero during the charge and discharge processes. To further investigate the practical application of the as-synthesized NiCo2O4 nanosheets-based electrode, a device was assembled with the as-prepared samples as the positive electrode and active carbon (AC) as the negative electrode. The assembled supercapacitor showed energy densities of 0.14 and 0.09 Wh∙cm-3 at 1.56 and 4.5 W∙cm-3, respectively. Furthermore, it was able to maintain 95% of its initial specific capacitance after 10000 cycles. The excellent electrochemical performance of the NiCo2O4 nanosheets could be ascribed to their unique spatial structure composed of interconnected ultrathin nanosheets, which facilitated electron transportation and ion penetration, suggesting their potential applications as electrode materials for high performance supercapacitors. The present synthetic route can be extended to other ternary transition metal oxides/sulfides for future energy storage devices and systems. ![]()
The looming global energy crisis and ever-increasing energy demands have catalyzed the development of renewable energy storage systems. In this regard, supercapacitors (SCs) have attracted widespread attention because of their advantageous attributes such as high power density, excellent cycle stability, and environmental friendliness. However, SCs exhibit low energy density and it is important to optimize electrode materials to improve the overall performance of these devices. Among the various electrode materials available, spinel nickel cobaltate (NiCo2O4) is particularly interesting because of its excellent theoretical capacitance. Based on the understanding that the performances of the electrode materials strongly depend on their morphologies and structures, in this study, we successfully synthesized NiCo2O4 nanosheets on Ni foam via a simple hydrothermal route followed by calcination. The structures and morphologies of the as-synthesized products were characterized by X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller (BET) surface area analysis, and the results showed that they were uniformly distributed on the Ni foam support. The surface chemical states of the elements in the samples were identified by X-ray photoelectron spectroscopy. The as-synthesized NiCo2O4 products were then tested as cathode materials for supercapacitors in a traditional three-electrode system. The electrochemical performances of the NiCo2O4 electrode materials were studied and the area capacitance was found to be 1.26 C∙cm-2 at a current density of 1 mA∙cm-2. Furthermore, outstanding cycling stability with 97.6% retention of the initial discharge capacitance after 10000 cycles and excellent rate performance (67.5% capacitance retention with the current density from 1 to 14 mA∙cm-2) were achieved. It was found that the Ni foam supporting the NiCo2O4 nanosheets increased the conductivity of the electrode materials. However, it is worth noting that the contribution of nickel foam to the areal capacitance of the electrode materials was almost zero during the charge and discharge processes. To further investigate the practical application of the as-synthesized NiCo2O4 nanosheets-based electrode, a device was assembled with the as-prepared samples as the positive electrode and active carbon (AC) as the negative electrode. The assembled supercapacitor showed energy densities of 0.14 and 0.09 Wh∙cm-3 at 1.56 and 4.5 W∙cm-3, respectively. Furthermore, it was able to maintain 95% of its initial specific capacitance after 10000 cycles. The excellent electrochemical performance of the NiCo2O4 nanosheets could be ascribed to their unique spatial structure composed of interconnected ultrathin nanosheets, which facilitated electron transportation and ion penetration, suggesting their potential applications as electrode materials for high performance supercapacitors. The present synthetic route can be extended to other ternary transition metal oxides/sulfides for future energy storage devices and systems.
2020, 36(7): 190502
doi: 10.3866/PKU.WHXB201905023
Abstract:
Alcohols fuel electro-oxidation is significant to the development of direct alcohols fuel cells, that are considered as a promising power source for portable electronic devices. Currently, the catalyst was restricted by the serious poisoning effect and high cost of noble metals. Developing low-cost Pt alloy with high performance and anti-CO poisoning ability was highly desired. In this work, PtCo-NC catalyst was synthesized by combining Pt nanoparticles with ZIF-67 after annealing in the tube furnace and the in situ generated N-doped carbon from ZIF-67 was functionalized to support the PtCo alloy nanoparticle. The structure and morphology were probed by X-ray diffraction, scanning electron microscope and transmission electron microscope, and the electrochemical performance was evaluated for alcohols of methanol and ethanol oxidation in the acid electrolyte. Compared with the reference sample of Pt/C, several times performance enhancement for alcohols fuel oxidation was found on PtCo-NC catalyst as well as the good catalytic stability. Specifically, the peak current density of PtCo-NC was 79.61 mA∙cm−2 for methanol oxidation, about 2.2 times higher than that of the Pt/C electrode (36.97 mA∙cm−2) and 2.5 times higher than that of the commercial Pt/C electrode (31.23 mA∙cm−2); it was 62.69 mA∙cm–2 for ethanol oxidation, about 1.65 times higher than that of Pt/C catalyst (37.99 mA∙cm−2) and commercial Pt/C electrode (37.77 mA∙cm−2). These catalytic performances were also much higher than some analogous catalysts developed for alcohols fuel oxidation. A much higher anti-CO poisoning ability was demonstrated by the CO stripping voltammetry experiment, in which the COad oxidation peak potential for PtCo-NC was 0.46 V, ca. 110 mV negative shift compared with Pt/C catalyst at 0.57 V. A strong electronic effect was indicated by the peak position shifting to the lower binding energy direction by 0.3 eV on PtCo-NC compared with Pt/C reference catalyst. According to the d-band center theory, the electron-enriched state of Pt will decrease the interaction strength of poisoning intermediates adsorbed on its surface; Moreover, according to the bifunctional catalytic mechanism, the presence of Co can form the adsorbed oxygen-containing species (―OH) more easily than Pt at low potentials, and this oxygen-species were helpful in the oxidation of COad at neighboring Pt sites. The high catalytic performance for alcohols fuel oxidation could be due to the largely improved anti-CO poisoning ability and the synergistic effect between the in situ formed PtCo nanoparticles and the N-doped carbon support. ![]()
Alcohols fuel electro-oxidation is significant to the development of direct alcohols fuel cells, that are considered as a promising power source for portable electronic devices. Currently, the catalyst was restricted by the serious poisoning effect and high cost of noble metals. Developing low-cost Pt alloy with high performance and anti-CO poisoning ability was highly desired. In this work, PtCo-NC catalyst was synthesized by combining Pt nanoparticles with ZIF-67 after annealing in the tube furnace and the in situ generated N-doped carbon from ZIF-67 was functionalized to support the PtCo alloy nanoparticle. The structure and morphology were probed by X-ray diffraction, scanning electron microscope and transmission electron microscope, and the electrochemical performance was evaluated for alcohols of methanol and ethanol oxidation in the acid electrolyte. Compared with the reference sample of Pt/C, several times performance enhancement for alcohols fuel oxidation was found on PtCo-NC catalyst as well as the good catalytic stability. Specifically, the peak current density of PtCo-NC was 79.61 mA∙cm−2 for methanol oxidation, about 2.2 times higher than that of the Pt/C electrode (36.97 mA∙cm−2) and 2.5 times higher than that of the commercial Pt/C electrode (31.23 mA∙cm−2); it was 62.69 mA∙cm–2 for ethanol oxidation, about 1.65 times higher than that of Pt/C catalyst (37.99 mA∙cm−2) and commercial Pt/C electrode (37.77 mA∙cm−2). These catalytic performances were also much higher than some analogous catalysts developed for alcohols fuel oxidation. A much higher anti-CO poisoning ability was demonstrated by the CO stripping voltammetry experiment, in which the COad oxidation peak potential for PtCo-NC was 0.46 V, ca. 110 mV negative shift compared with Pt/C catalyst at 0.57 V. A strong electronic effect was indicated by the peak position shifting to the lower binding energy direction by 0.3 eV on PtCo-NC compared with Pt/C reference catalyst. According to the d-band center theory, the electron-enriched state of Pt will decrease the interaction strength of poisoning intermediates adsorbed on its surface; Moreover, according to the bifunctional catalytic mechanism, the presence of Co can form the adsorbed oxygen-containing species (―OH) more easily than Pt at low potentials, and this oxygen-species were helpful in the oxidation of COad at neighboring Pt sites. The high catalytic performance for alcohols fuel oxidation could be due to the largely improved anti-CO poisoning ability and the synergistic effect between the in situ formed PtCo nanoparticles and the N-doped carbon support.
2020, 36(7): 190505
doi: 10.3866/PKU.WHXB201905056
Abstract:
Graphite phase carbon nitride (g-C3N4) has shown excellent potential when applied to photocatalytic hydrogen (H2) generation upon exposure to visible light. However, the photocatalytic activity during hydrogen generation remains very low because of the high recombination rate of photogenerated electron-hole pairs and poor conductivity. Of the various strategies to improve H2 generation efficiency, N vacancies have proven to be effective at increasing the photocatalytic performance of g-C3N4. However, creating a N vacancy is primarily dependent on the post-heating of g-C3N4 in air at an elevated temperature, which generates a high concentration of N vacancies and consequent decreased crystallinity of g-C3N4. Thus, as-produced g-C3N4 offers low photocatalytic efficiency owing to the high recombination rate of photogenerated electron-hole pairs. Currently, controlling the concentration of N vacancy in g-C3N4 is an immense challenge. Herein, we report an effective means of achieving controllable N vacancies in g-C3N4 via urea in-situ generated NH3 at an elevated temperature. Specifically, g-C3N4 was first prepared with dicyandiamide as a precursor and subjected to rapid post-thermal treatment at 650 ℃ in a tubular furnace for 10 min, in which a desired amount of urea was mixed with g-C3N4 as the source material for NH3. X-ray diffraction analysis showed increased crystallinity and an unchanged crystal structure as compared to pristine g-C3N4. X-ray photoelectron spectroscopy and elemental analysis verified the reduced levels of N-vacancy concentration with urea added as the NH3 source when compared to the g-C3N4 post-heated in air without the addition of urea. In addition, UV-Vis spectra displayed an increased visible light absorption due to the generated N vacancies. Moreover, the specific surface area of g-C3N4 was progressively enlarged with an increase in the amount of urea added. The high crystallinity, low N-vacancy concentration, increased light absorption, and enlarged surface area translated into markedly increased photocatalytic H2 generation. The highest H2 generation rate from the optimized added amount of urea was 6.5 μmol·h-1, which was three times higher than that when using a g-C3N4 sample thermally treated without urea addition. The H2 generation enhancement was also the result of the increased separation efficiency of photogenerated electron-hole pairs as exemplified by the significantly decreased photoluminescence spectra and large transient photocurrent. The results of this study demonstrate the simultaneous production of highly crystalline g-C3N4 and controllable creation of N vacancy by in-situ generated NH3 through thermal decomposition of urea. This study reveals the immense potential of NH3 at controlling the N-vacancy concentration of g-C3N4 for increased photocatalytic H2 generation. ![]()
Graphite phase carbon nitride (g-C3N4) has shown excellent potential when applied to photocatalytic hydrogen (H2) generation upon exposure to visible light. However, the photocatalytic activity during hydrogen generation remains very low because of the high recombination rate of photogenerated electron-hole pairs and poor conductivity. Of the various strategies to improve H2 generation efficiency, N vacancies have proven to be effective at increasing the photocatalytic performance of g-C3N4. However, creating a N vacancy is primarily dependent on the post-heating of g-C3N4 in air at an elevated temperature, which generates a high concentration of N vacancies and consequent decreased crystallinity of g-C3N4. Thus, as-produced g-C3N4 offers low photocatalytic efficiency owing to the high recombination rate of photogenerated electron-hole pairs. Currently, controlling the concentration of N vacancy in g-C3N4 is an immense challenge. Herein, we report an effective means of achieving controllable N vacancies in g-C3N4 via urea in-situ generated NH3 at an elevated temperature. Specifically, g-C3N4 was first prepared with dicyandiamide as a precursor and subjected to rapid post-thermal treatment at 650 ℃ in a tubular furnace for 10 min, in which a desired amount of urea was mixed with g-C3N4 as the source material for NH3. X-ray diffraction analysis showed increased crystallinity and an unchanged crystal structure as compared to pristine g-C3N4. X-ray photoelectron spectroscopy and elemental analysis verified the reduced levels of N-vacancy concentration with urea added as the NH3 source when compared to the g-C3N4 post-heated in air without the addition of urea. In addition, UV-Vis spectra displayed an increased visible light absorption due to the generated N vacancies. Moreover, the specific surface area of g-C3N4 was progressively enlarged with an increase in the amount of urea added. The high crystallinity, low N-vacancy concentration, increased light absorption, and enlarged surface area translated into markedly increased photocatalytic H2 generation. The highest H2 generation rate from the optimized added amount of urea was 6.5 μmol·h-1, which was three times higher than that when using a g-C3N4 sample thermally treated without urea addition. The H2 generation enhancement was also the result of the increased separation efficiency of photogenerated electron-hole pairs as exemplified by the significantly decreased photoluminescence spectra and large transient photocurrent. The results of this study demonstrate the simultaneous production of highly crystalline g-C3N4 and controllable creation of N vacancy by in-situ generated NH3 through thermal decomposition of urea. This study reveals the immense potential of NH3 at controlling the N-vacancy concentration of g-C3N4 for increased photocatalytic H2 generation.
2020, 36(7): 190606
doi: 10.3866/PKU.WHXB201906069
Abstract:
Materials such as metals, semiconductors, and oxides are attractive at nanometer scales due to the physical and chemical property differences with their bulk counterparts as induced by the quantum confinement effect and large surface-to-volume ratios. In particular, heterogeneous nanostructures consisting of semiconductors and noble metals are extremely important because of the synergistic effects occurring at the interfaces between their noble metal and semiconductor domains; these often equip the heterogeneous nanostructures with improved properties compared to those of isolated individual components. Thus far, heterogeneous nanostructures have garnered a considerable research interest, and tremendous development in achieving high degree control over these nanostructures with respect to their domain size, morphology, and composition has been realized. Their immense application potential in optics, catalysis, imaging, and biomedicine render them a field full of original innovation possibilities. Herein, we demonstrate a phenomenon observed in core-shell nanostructures composed of noble metals and silver sulfide (Ag2S): the inside-out migration of noble metals in Ag2S nanoparticles. We prepare core-shell nanostructures with noble metals and Ag2S residing at the core and shell regions, respectively, through various synthetic strategies including seed-mediated growth and galvanic replacement reactions followed by sulfidation. We then characterize the core-shell nanostructures before and after aging them in toluene at room temperature (e.g. 25 ℃) for a period of time up to 72 h. In contrast to the reported diffusion of Au from the outside to the inside of InAs or PbTe nanoparticles, which results in an Au core encapsulated by an amorphous InAs or PbTe shell, the noble metals (Au, Ag, Pd, or Pt) in core-shell nanostructures with noble metals and Ag2S residing at the core and shell regions, respectively, are found to diffuse from the inside to the outside through the Ag2S shell. Thus, heterogeneous nanodimers consisting of the corresponding noble metal and Ag2S are formed. Observations using an electron transmission microscope confirm that the inside-out migration of noble metals in Ag2S is carried out in a holistic manner. Due to the apparent interface mismatch between face-centered cubic noble metals and monoclinic Ag2S crystal phases, defects such as vacancies must exist at these interfaces. This makes the migration of noble metals in Ag2S possible by either a vacancy/substitutional mechanism or by the self-purification mechanism that occurs intrinsically in nanoscale semiconductors. As the migration rate of noble metals in Ag2S increases with the decrease in the size of the noble metal core and the radius of noble metal atoms, the inside-out migration rates of Ag, Pd, and Pt in Ag2S are found to be much higher than that of Au because of their smaller particle sizes or atom radii. This scientific phenomenon can be effective in the development of synthetic routes for heterogeneous nanostructures that might not be obtained by conventional methods. ![]()
Materials such as metals, semiconductors, and oxides are attractive at nanometer scales due to the physical and chemical property differences with their bulk counterparts as induced by the quantum confinement effect and large surface-to-volume ratios. In particular, heterogeneous nanostructures consisting of semiconductors and noble metals are extremely important because of the synergistic effects occurring at the interfaces between their noble metal and semiconductor domains; these often equip the heterogeneous nanostructures with improved properties compared to those of isolated individual components. Thus far, heterogeneous nanostructures have garnered a considerable research interest, and tremendous development in achieving high degree control over these nanostructures with respect to their domain size, morphology, and composition has been realized. Their immense application potential in optics, catalysis, imaging, and biomedicine render them a field full of original innovation possibilities. Herein, we demonstrate a phenomenon observed in core-shell nanostructures composed of noble metals and silver sulfide (Ag2S): the inside-out migration of noble metals in Ag2S nanoparticles. We prepare core-shell nanostructures with noble metals and Ag2S residing at the core and shell regions, respectively, through various synthetic strategies including seed-mediated growth and galvanic replacement reactions followed by sulfidation. We then characterize the core-shell nanostructures before and after aging them in toluene at room temperature (e.g. 25 ℃) for a period of time up to 72 h. In contrast to the reported diffusion of Au from the outside to the inside of InAs or PbTe nanoparticles, which results in an Au core encapsulated by an amorphous InAs or PbTe shell, the noble metals (Au, Ag, Pd, or Pt) in core-shell nanostructures with noble metals and Ag2S residing at the core and shell regions, respectively, are found to diffuse from the inside to the outside through the Ag2S shell. Thus, heterogeneous nanodimers consisting of the corresponding noble metal and Ag2S are formed. Observations using an electron transmission microscope confirm that the inside-out migration of noble metals in Ag2S is carried out in a holistic manner. Due to the apparent interface mismatch between face-centered cubic noble metals and monoclinic Ag2S crystal phases, defects such as vacancies must exist at these interfaces. This makes the migration of noble metals in Ag2S possible by either a vacancy/substitutional mechanism or by the self-purification mechanism that occurs intrinsically in nanoscale semiconductors. As the migration rate of noble metals in Ag2S increases with the decrease in the size of the noble metal core and the radius of noble metal atoms, the inside-out migration rates of Ag, Pd, and Pt in Ag2S are found to be much higher than that of Au because of their smaller particle sizes or atom radii. This scientific phenomenon can be effective in the development of synthetic routes for heterogeneous nanostructures that might not be obtained by conventional methods.
2020, 36(7): 190700
doi: 10.3866/PKU.WHXB201907001
Abstract:
Platinum (Pt) is recognized as an excellent cocatalyst which not only suppresses the charge carrier recombination of the photocatalyst but also reduces the overpotential for photocatalytic H2 generation. Albeit of its good performance, the high cost and low abundance restricted the utilization of Pt in large-scale photocatalytic H2 generation. Pt based transition metal alloys are demonstrated to reveal enhanced activities towards various catalytic reactions, suggesting the possibility to substitute Pt as the cocatalyst. In the present work, Pt was partially substituted with Co, Ni, and Fe and Pt-M (M = Co, Ni, and Fe)/g-C3N4 composites were constructed through co-reduction of H2PtCl6 and transition metal salts by the reductant of ethylene glycol. The crystal structure and valence states were measured by X-ray diffractometer (XRD) and X-ray photoelectron spectrometer (XPS), respectively. The higher degree of XRD peaks and larger binding energies for Pt 4f5/2 and Pt 4f7/2 after incorporating Co2+ ions indicated that Co was successfully introduced into the lattice of Pt and Pt-Co bimetallic alloys was attained through the solvothermal treatment. The morphology was subsequently observed by transmission electron microscope (TEM), which showed a good dispersion of Pt-Co nanoparticles on the surface of g-C3N4. Meanwhile, the shrinkage of lattice fringe after introducing cobalt salt further confirmed the presence of Pt-Co bimetallic alloys. The UV-Vis absorption spectra of g-C3N4 and Pt, Pt-Co deposited g-C3N4 were subsequently performed. It was found that the absorption edges were all consistent for all three samples as anticipated, implying that the band gap energy was maintained after hybridizing with Pt or Pt-Co alloys. Furthermore, the photocatalytic H2 generation was carried out over the as-prepared composites with triethanolamine (TEOA) as sacrificial reagent. Under visible-light illumination, the1% (w) Pt2.5M/g-C3N4 (M = Co, Fe, Ni) composites all exhibited higher or comparable activity towards photocatalytic H2 generation when compared to 1% (w) Pt loaded counterpart. In addition, the atomic ratios of Pt/Co and the loading amount of Pt-Co cocatalyst were modified to optimize the photocatalytic performance, among which, 1% (w) Pt2.5Co/g-C3N4 composite revealed the highest activity with a 1.6-time enhancement. Electrochemical impedance spectra (EIS) and photoluminescence (PL) spectra indicated that the enhancement might be attributed to improved charge transfer from g-C3N4 to Pt2.5Co cocatalyst and inhibited charge carrier recombination in the presence of Pt2.5Co cocatalyst. Therefore, the present study demonstrates the great potential to partially replace Pt with low-cost and abundant transition metals and to fabricate Pt based bimetallic alloys as promising cocatalysts for highly efficient photocatalytic H2 generation. ![]()
Platinum (Pt) is recognized as an excellent cocatalyst which not only suppresses the charge carrier recombination of the photocatalyst but also reduces the overpotential for photocatalytic H2 generation. Albeit of its good performance, the high cost and low abundance restricted the utilization of Pt in large-scale photocatalytic H2 generation. Pt based transition metal alloys are demonstrated to reveal enhanced activities towards various catalytic reactions, suggesting the possibility to substitute Pt as the cocatalyst. In the present work, Pt was partially substituted with Co, Ni, and Fe and Pt-M (M = Co, Ni, and Fe)/g-C3N4 composites were constructed through co-reduction of H2PtCl6 and transition metal salts by the reductant of ethylene glycol. The crystal structure and valence states were measured by X-ray diffractometer (XRD) and X-ray photoelectron spectrometer (XPS), respectively. The higher degree of XRD peaks and larger binding energies for Pt 4f5/2 and Pt 4f7/2 after incorporating Co2+ ions indicated that Co was successfully introduced into the lattice of Pt and Pt-Co bimetallic alloys was attained through the solvothermal treatment. The morphology was subsequently observed by transmission electron microscope (TEM), which showed a good dispersion of Pt-Co nanoparticles on the surface of g-C3N4. Meanwhile, the shrinkage of lattice fringe after introducing cobalt salt further confirmed the presence of Pt-Co bimetallic alloys. The UV-Vis absorption spectra of g-C3N4 and Pt, Pt-Co deposited g-C3N4 were subsequently performed. It was found that the absorption edges were all consistent for all three samples as anticipated, implying that the band gap energy was maintained after hybridizing with Pt or Pt-Co alloys. Furthermore, the photocatalytic H2 generation was carried out over the as-prepared composites with triethanolamine (TEOA) as sacrificial reagent. Under visible-light illumination, the1% (w) Pt2.5M/g-C3N4 (M = Co, Fe, Ni) composites all exhibited higher or comparable activity towards photocatalytic H2 generation when compared to 1% (w) Pt loaded counterpart. In addition, the atomic ratios of Pt/Co and the loading amount of Pt-Co cocatalyst were modified to optimize the photocatalytic performance, among which, 1% (w) Pt2.5Co/g-C3N4 composite revealed the highest activity with a 1.6-time enhancement. Electrochemical impedance spectra (EIS) and photoluminescence (PL) spectra indicated that the enhancement might be attributed to improved charge transfer from g-C3N4 to Pt2.5Co cocatalyst and inhibited charge carrier recombination in the presence of Pt2.5Co cocatalyst. Therefore, the present study demonstrates the great potential to partially replace Pt with low-cost and abundant transition metals and to fabricate Pt based bimetallic alloys as promising cocatalysts for highly efficient photocatalytic H2 generation.
2020, 36(7): 190701
doi: 10.3866/PKU.WHXB201907011
Abstract:
Along with the promising applications of lanthanide doped upconversion nanomaterials in diverse fields such as biology, anti-counterfeiting, and lasering, the demand for multifunctional upconversion nanomaterials is increasing. One effective means of obtaining these nanomaterials is to fabricate upconversion nanomaterial-based heterostructures, which may provide superior properties as compared to the sum of the parts. However, obtaining heterostructured upconversion nanomaterials remains challenging mainly because of the crystal lattice mismatch between upconversion nanomaterials and other materials. Typically used strategies for synthesizing upconversion nanomaterial-based heterostructures are applicable only to limited types of materials. Alternatively, transformation of the intermediate layer is a promising strategy used to obtain these heterostructures. Nevertheless, this method remains in its infancy and, to date, only a few intermediate layers have been developed. New types of intermediate layers are therefore highly desirable. In this study, we show that amorphous Y(OH)CO3 can be a promising candidate as an intermediate layer for fabricating upconversion nanoparticle-based heterostructures. As a proof-of-concept experiment, ligand-free NaGdF4:Yb/Tm upconversion nanoparticles were first prepared as core nanoparticles. The Y(OH)CO3 shell was then directly coated on the NaGdF4:Yb/Tm upconversion nanoparticles in an aqueous solution using urea and Y(NO3)3, by a homogeneous precipitation approach. The thickness of the resulting Y(OH)CO3 shell could be tuned by adjusting the amounts of either urea or Y(NO3)3. The as-coated Y(OH)CO3 shell could be easily converted to YOF by heating at 300 ℃, yielding NaGdF4:Yb/Tm@YOF core-shell heterostructured nanoparticles. In addition, we found that the NaGdF4 core could be transformed to lanthanide oxide fluoride if the NaGdF4:Yb/Tm@Y(OH)CO3 core-shell nanoparticles were heated at 350 ℃. We also observed that treating the NaGdF4:Yb/Tm@Y(OH)CO3 core-shell nanoparticles at even higher temperatures (e.g., 400 ℃) produced aggregations of nanoparticles without regular morphologies. The transformation of the shell can be attributed to the decomposition of Y(OH)CO3 and reactions between the Y(OH)CO3 shell and NaGdF4 core. Meanwhile, the transformation of the NaGdF4 core at relatively high temperatures could be primarily due to the reactions between Y(OH)CO3 and NaGdF4. Notably, in this study, the core-shell structured nanoparticles, with either a Y(OH)CO3 or YOF shell, maintained the photon upconversion properties of NaGdF4:Yb/Tm upconversion nanoparticles. In addition, the method used here could be extended to the coating of other shells such as Tb(OH)CO3 and Yb(OH)CO3 on upconversion nanoparticles. Moreover, the NaGdF4:Yb/Tm@Y(OH)CO3 core-shell nanoparticles could be transformed to other nanoparticles with novel structures such as yolk-shell nanoparticles. These results can pave the way for preparing upconversion nanoparticle-based heterostructures and multifunctional composites, thus promoting new applications of upconversion nanoparticles. ![]()
Along with the promising applications of lanthanide doped upconversion nanomaterials in diverse fields such as biology, anti-counterfeiting, and lasering, the demand for multifunctional upconversion nanomaterials is increasing. One effective means of obtaining these nanomaterials is to fabricate upconversion nanomaterial-based heterostructures, which may provide superior properties as compared to the sum of the parts. However, obtaining heterostructured upconversion nanomaterials remains challenging mainly because of the crystal lattice mismatch between upconversion nanomaterials and other materials. Typically used strategies for synthesizing upconversion nanomaterial-based heterostructures are applicable only to limited types of materials. Alternatively, transformation of the intermediate layer is a promising strategy used to obtain these heterostructures. Nevertheless, this method remains in its infancy and, to date, only a few intermediate layers have been developed. New types of intermediate layers are therefore highly desirable. In this study, we show that amorphous Y(OH)CO3 can be a promising candidate as an intermediate layer for fabricating upconversion nanoparticle-based heterostructures. As a proof-of-concept experiment, ligand-free NaGdF4:Yb/Tm upconversion nanoparticles were first prepared as core nanoparticles. The Y(OH)CO3 shell was then directly coated on the NaGdF4:Yb/Tm upconversion nanoparticles in an aqueous solution using urea and Y(NO3)3, by a homogeneous precipitation approach. The thickness of the resulting Y(OH)CO3 shell could be tuned by adjusting the amounts of either urea or Y(NO3)3. The as-coated Y(OH)CO3 shell could be easily converted to YOF by heating at 300 ℃, yielding NaGdF4:Yb/Tm@YOF core-shell heterostructured nanoparticles. In addition, we found that the NaGdF4 core could be transformed to lanthanide oxide fluoride if the NaGdF4:Yb/Tm@Y(OH)CO3 core-shell nanoparticles were heated at 350 ℃. We also observed that treating the NaGdF4:Yb/Tm@Y(OH)CO3 core-shell nanoparticles at even higher temperatures (e.g., 400 ℃) produced aggregations of nanoparticles without regular morphologies. The transformation of the shell can be attributed to the decomposition of Y(OH)CO3 and reactions between the Y(OH)CO3 shell and NaGdF4 core. Meanwhile, the transformation of the NaGdF4 core at relatively high temperatures could be primarily due to the reactions between Y(OH)CO3 and NaGdF4. Notably, in this study, the core-shell structured nanoparticles, with either a Y(OH)CO3 or YOF shell, maintained the photon upconversion properties of NaGdF4:Yb/Tm upconversion nanoparticles. In addition, the method used here could be extended to the coating of other shells such as Tb(OH)CO3 and Yb(OH)CO3 on upconversion nanoparticles. Moreover, the NaGdF4:Yb/Tm@Y(OH)CO3 core-shell nanoparticles could be transformed to other nanoparticles with novel structures such as yolk-shell nanoparticles. These results can pave the way for preparing upconversion nanoparticle-based heterostructures and multifunctional composites, thus promoting new applications of upconversion nanoparticles.
2020, 36(7): 190707
doi: 10.3866/PKU.WHXB201907072
Abstract:
The development of high-performance supercapacitor electrode materials is imperative to alleviate the ongoing energy crisis. Numerous transition metals (oxides) have been studied as electrode materials for supercapacitors owing to their low cost, environmental-friendliness, and excellent electrochemical performance. Among the developed binary transition metal oxides, manganese cobalt oxides typically show high theoretical capacitance and stable electrochemical performance, and are widely used in the electrode materials of supercapacitors. However, the poor conductivity and active material utilization of manganese cobalt oxide-based electrode materials limit their potential capacitance application. Cotton is mainly composed of organic carbon-containing materials, which can be transformed to carbon fibers after calcination. The resultant carbonaceous material exhibits a large specific surface area and good conductivity. Such advantages could potentially suppress the negative effects caused by the poor conductivity and small specific surface area of manganese cobalt oxides, thereby improving the electrochemical performance. Herein, we firstly deposited manganese cobalt oxides on cotton by a simple hydrothermal method, yielding a composite of manganese cobalt oxides and carbon fibers via subsequent calcination, to improve the electrochemical performance of the electrode material. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), and electrochemical characterizations were used to investigate the physical, chemical, and electrochemical properties of the prepared samples. The fabricated manganese cobalt oxides in the composite were uniformly dispersed on the carbon fiber surface, which increased the contact between the interface of the electrode material and electrolyte, and enhanced electrode material utilization. The electrode material was confirmed to have well contacted with the electrolyte during a contact angle test. Hence, a pseudo-capacitance reaction completely occurred on the manganese cobalt oxide material. Moreover, the addition of carbon fibers reduced the resistance of the material, resulting in excellent capacitive performance. The capacitance of the prepared composite was 854 F∙g-1 at a current density of 2 A∙g-1. The capacitance was maintained at 72.3% after 2000 cycles at a current density of 2 A∙g-1. These results indicate that the manganese cobalt oxide and carbon fiber composite is a promising electrode material for high-performance supercapacitors. The findings presented herein provide a strategy for coupling with carbon materials to enhance the performance of supercapacitor electrode materials based on manganese cobalt oxides. Thus, novel insights into the design of high-performance supercapacitors for energy management are provided. ![]()
The development of high-performance supercapacitor electrode materials is imperative to alleviate the ongoing energy crisis. Numerous transition metals (oxides) have been studied as electrode materials for supercapacitors owing to their low cost, environmental-friendliness, and excellent electrochemical performance. Among the developed binary transition metal oxides, manganese cobalt oxides typically show high theoretical capacitance and stable electrochemical performance, and are widely used in the electrode materials of supercapacitors. However, the poor conductivity and active material utilization of manganese cobalt oxide-based electrode materials limit their potential capacitance application. Cotton is mainly composed of organic carbon-containing materials, which can be transformed to carbon fibers after calcination. The resultant carbonaceous material exhibits a large specific surface area and good conductivity. Such advantages could potentially suppress the negative effects caused by the poor conductivity and small specific surface area of manganese cobalt oxides, thereby improving the electrochemical performance. Herein, we firstly deposited manganese cobalt oxides on cotton by a simple hydrothermal method, yielding a composite of manganese cobalt oxides and carbon fibers via subsequent calcination, to improve the electrochemical performance of the electrode material. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), and electrochemical characterizations were used to investigate the physical, chemical, and electrochemical properties of the prepared samples. The fabricated manganese cobalt oxides in the composite were uniformly dispersed on the carbon fiber surface, which increased the contact between the interface of the electrode material and electrolyte, and enhanced electrode material utilization. The electrode material was confirmed to have well contacted with the electrolyte during a contact angle test. Hence, a pseudo-capacitance reaction completely occurred on the manganese cobalt oxide material. Moreover, the addition of carbon fibers reduced the resistance of the material, resulting in excellent capacitive performance. The capacitance of the prepared composite was 854 F∙g-1 at a current density of 2 A∙g-1. The capacitance was maintained at 72.3% after 2000 cycles at a current density of 2 A∙g-1. These results indicate that the manganese cobalt oxide and carbon fiber composite is a promising electrode material for high-performance supercapacitors. The findings presented herein provide a strategy for coupling with carbon materials to enhance the performance of supercapacitor electrode materials based on manganese cobalt oxides. Thus, novel insights into the design of high-performance supercapacitors for energy management are provided.
2020, 36(7): 191101
doi: 10.3866/PKU.WHXB201911016
Abstract:
In this study, pure Bi2MoO6 was synthesized via a solvothermal method. A ZnCuAl-layered double hydroxide (LDH)/Bi2MoO6 (denoted as LDH/Bi2MoO6) nanocomposite was synthesized via a steady-state co-precipitation route using Bi2MoO6 as the matric material. LDH was deposited on the surface of Bi2MoO6 with a close contact interface. The specific surface area of the resulting LDH/Bi2MoO6 composite increased up to 19.1 m2∙g−1 owing to the stacking arrangement between LDH and the Bi2MoO6 nanosheets, resulting in the generation of a large number of reactive sites. In addition, the light absorption region of the LDH/Bi2MoO6 composite was larger than those of pure LDH and Bi2MoO6 because of the formation of a heterojunction structure and the possible quantum size effect. The photocatalytic performance of the as-prepared samples was evaluated by carrying out the degradation of rhodamine B (RhB) using them under visible light irradiation. Compared to pure LDH and Bi2MoO6, the LDH/Bi2MoO6 nanocomposite exhibited enhanced photocatalytic activity for the degradation of RhB. With an increase in the LDH content, the photocatalytic activity of the LDH/Bi2MoO6 composite first increased and then decreased. Although the addition of an optimum amount of LDH was beneficial for the generation of electron-hole pairs, excessive LDH on the surface of Bi2MoO6 decreased the visible light absorption ability of both the components, thus reducing photocatalytic activity of the composite. This indicates that an appropriate LDH:Bi2MoO6 molar ratio is necessary for obtaining LDH/Bi2MoO6 composites with excellent photocatalytic activity. Furthermore, the LDH/Bi2MoO6 composite showed high photocatalytic stability and reusability. The structure of the LDH/Bi2MoO6 composite remained almost unchanged even after four photodegradation cycles. The enhanced photocatalytic performance of the composite can be attributed to the combined effect of its heterojunction structure and high specific surface area, which are beneficial for effective separation of photogenerated charge carriers and the availability of a large number of active sites for photocatalysis. It was found that •OH and O2•− were the main reactive species, while e− and h+ contributed little to the photodegradation process. The generation, transfer, and separation of photoinduced electrons and holes in the composites were investigated by transient photocurrent responses, electrochemical impedance spectroscopy Nyquist plots, and photoluminescence measurements. The results showed that the heterojunction structure of the composites played a key role in enhancing their photocatalytic activity. A possible photodegradation mechanism was proposed for the composite. This study will provide a facile approach for the preparation of LDH- and/or Bi2MoO6-based nanocomposites. The LDH/Bi2MoO6 nanocomposite prepared in this study showed huge potential to be used as a visible-light photocatalyst for degrading environmental pollutants. ![]()
In this study, pure Bi2MoO6 was synthesized via a solvothermal method. A ZnCuAl-layered double hydroxide (LDH)/Bi2MoO6 (denoted as LDH/Bi2MoO6) nanocomposite was synthesized via a steady-state co-precipitation route using Bi2MoO6 as the matric material. LDH was deposited on the surface of Bi2MoO6 with a close contact interface. The specific surface area of the resulting LDH/Bi2MoO6 composite increased up to 19.1 m2∙g−1 owing to the stacking arrangement between LDH and the Bi2MoO6 nanosheets, resulting in the generation of a large number of reactive sites. In addition, the light absorption region of the LDH/Bi2MoO6 composite was larger than those of pure LDH and Bi2MoO6 because of the formation of a heterojunction structure and the possible quantum size effect. The photocatalytic performance of the as-prepared samples was evaluated by carrying out the degradation of rhodamine B (RhB) using them under visible light irradiation. Compared to pure LDH and Bi2MoO6, the LDH/Bi2MoO6 nanocomposite exhibited enhanced photocatalytic activity for the degradation of RhB. With an increase in the LDH content, the photocatalytic activity of the LDH/Bi2MoO6 composite first increased and then decreased. Although the addition of an optimum amount of LDH was beneficial for the generation of electron-hole pairs, excessive LDH on the surface of Bi2MoO6 decreased the visible light absorption ability of both the components, thus reducing photocatalytic activity of the composite. This indicates that an appropriate LDH:Bi2MoO6 molar ratio is necessary for obtaining LDH/Bi2MoO6 composites with excellent photocatalytic activity. Furthermore, the LDH/Bi2MoO6 composite showed high photocatalytic stability and reusability. The structure of the LDH/Bi2MoO6 composite remained almost unchanged even after four photodegradation cycles. The enhanced photocatalytic performance of the composite can be attributed to the combined effect of its heterojunction structure and high specific surface area, which are beneficial for effective separation of photogenerated charge carriers and the availability of a large number of active sites for photocatalysis. It was found that •OH and O2•− were the main reactive species, while e− and h+ contributed little to the photodegradation process. The generation, transfer, and separation of photoinduced electrons and holes in the composites were investigated by transient photocurrent responses, electrochemical impedance spectroscopy Nyquist plots, and photoluminescence measurements. The results showed that the heterojunction structure of the composites played a key role in enhancing their photocatalytic activity. A possible photodegradation mechanism was proposed for the composite. This study will provide a facile approach for the preparation of LDH- and/or Bi2MoO6-based nanocomposites. The LDH/Bi2MoO6 nanocomposite prepared in this study showed huge potential to be used as a visible-light photocatalyst for degrading environmental pollutants.
2020, 36(7): 190503
doi: 10.3866/PKU.WHXB201905034
Abstract:
Silicon is a promising anode material for lithium-ion batteries (LIBs) because of its natural abundance, high theoretical capacity, and relatively low working potential for lithium storage. However, two main obstacles exist that hinder its commercial application. One is the large volume variation during prolonged cycling, which causes irreversible cracking and disconnection of the active mass from the current collector and subsequently rapid decay of capacity of the electrode. The other is its poor intrinsic electronic conductivity, which seriously restricts its rate performance. To date, strategies to improve its cycling stability and rate capability include rational designs of different Si nanostructures and the incorporation of conductive agents. In this study, we present a novel and effective method to fabricate a Si/C composite. Through hydrogen bonding and the electrostatic interaction between graphene oxides (GO) and acidized chitosans (Cs), a hybrid hydrogel was fabricated in which silicon nanoparticles and carbon nanotubes were encapsulated in situ. Following freeze-drying and subsequent calcination, a three-dimensional porous silicon/carbon nanotube/graphene (Si-CNT@G) nanocomposite was obtained. The phase, structure, and morphology of the sample were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The results show that the silicon nanoparticles were uniformly distributed in the graphene network, which was interwoven with carbon nanotubes. The resultant Si-CNT@G nanocomposite featured a porous three-dimensional conductive carbonaceous support, providing short pathways for electrons, conductive transport highways for lithium ions, a sufficient interface for contact of the electrolyte and electrode, and an effective buffer matrix to alleviate structural change during discharge/charge cycling. Benefiting from these particular features, the as-prepared Si-CNT@G nanocomposite exhibited superior lithium storage performance with high specific capacity and excellent long-term cycling stability when evaluated as an anode material for LIBs. For example, a high discharge capacity of 673.7 mAh·g−1 can be retained after 200 discharge/charge cycles at a current density of 500 mA·g−1 in the potential range of 0.01–1.20 V, with a decent capacity retention of 97%. Even when at a current density of 2000 mA·g−1, a high discharge capacity of 566.9 mAh·g−1 can still be retained. In contrast, the discharge capacity of pure silicon nanoparticles, when tested under the same conditions, was practically nil. These results suggest that the Si-CNT@G nanocomposite is a promising anode material for high-performance LIBs.
Silicon is a promising anode material for lithium-ion batteries (LIBs) because of its natural abundance, high theoretical capacity, and relatively low working potential for lithium storage. However, two main obstacles exist that hinder its commercial application. One is the large volume variation during prolonged cycling, which causes irreversible cracking and disconnection of the active mass from the current collector and subsequently rapid decay of capacity of the electrode. The other is its poor intrinsic electronic conductivity, which seriously restricts its rate performance. To date, strategies to improve its cycling stability and rate capability include rational designs of different Si nanostructures and the incorporation of conductive agents. In this study, we present a novel and effective method to fabricate a Si/C composite. Through hydrogen bonding and the electrostatic interaction between graphene oxides (GO) and acidized chitosans (Cs), a hybrid hydrogel was fabricated in which silicon nanoparticles and carbon nanotubes were encapsulated in situ. Following freeze-drying and subsequent calcination, a three-dimensional porous silicon/carbon nanotube/graphene (Si-CNT@G) nanocomposite was obtained. The phase, structure, and morphology of the sample were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The results show that the silicon nanoparticles were uniformly distributed in the graphene network, which was interwoven with carbon nanotubes. The resultant Si-CNT@G nanocomposite featured a porous three-dimensional conductive carbonaceous support, providing short pathways for electrons, conductive transport highways for lithium ions, a sufficient interface for contact of the electrolyte and electrode, and an effective buffer matrix to alleviate structural change during discharge/charge cycling. Benefiting from these particular features, the as-prepared Si-CNT@G nanocomposite exhibited superior lithium storage performance with high specific capacity and excellent long-term cycling stability when evaluated as an anode material for LIBs. For example, a high discharge capacity of 673.7 mAh·g−1 can be retained after 200 discharge/charge cycles at a current density of 500 mA·g−1 in the potential range of 0.01–1.20 V, with a decent capacity retention of 97%. Even when at a current density of 2000 mA·g−1, a high discharge capacity of 566.9 mAh·g−1 can still be retained. In contrast, the discharge capacity of pure silicon nanoparticles, when tested under the same conditions, was practically nil. These results suggest that the Si-CNT@G nanocomposite is a promising anode material for high-performance LIBs.
2020, 36(7): 190607
doi: 10.3866/PKU.WHXB201906070
Abstract:
The exploitation of high-performing stable oxygen reduction reaction (ORR) electrocatalysts is critical for energy storage and conversion technologies. The existing high-efficiency electrocatalysts applied to the ORR are mainly based on Pt and its alloys. Moreover, carrier catalysts are the most widely used in actual electrocatalysis. A suitable carrier not only improves the utilization rate of precious metals and the service life of the catalyst, but also serves as a co-catalyst to ameliorate the catalytic activity through a synergistic effect in the reaction. Therefore, research into Pt-based electrocatalysts mainly focuses on the precious metal Pt and the carrier. With the aim of improving the activity and durability of Pt-based catalysts for the ORR, one-dimensional porous titanium nitride (TiN) nanotubes with a large specific surface area as well as good conductivity, electrochemical stability, and corrosion resistance were prepared in this study, and then, Pt nanoparticles were deposited on the TiN-support by atomic layer deposition (ALD). ALD is a novel and simple method for the preparation of films or nanoparticles with fine control of the thickness or size, respectively. The results of X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) experiments confirmed that the Pt nanoparticles obtained by ALD (ALD-Pt/TiN) were face-centered cubic (fcc) crystals with a uniform size and were highly dispersed on the surface of TiN. X-ray spectroscopy (XPS) measurements verified that the binding energy of Pt 4f in ALD-Pt/TiN was positively shifted by 0.33 eV with respect to that of the Pt/C catalyst, indicating strong electronic interactions between the ALD-Pt nanoparticles and the TiN carriers. Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) analyses revealed that ALD-Pt/TiN possessed high activity for the ORR and favorable durability. The onset potential and diffusion-limiting current density of ALD-Pt/TiN were similar to those of commercial Pt/C, while the half-wave potential was 20 mV higher than that of commercial Pt/C, indicating better electrocatalytic performance of the designed material. Furthermore, the electrocatalytic mechanism and kinetics for ALD-Pt/TiN were investigated by rotating ring-disc electrode (RRDE) experiments. The results suggested that the electron transfer number of the ALD-Pt/TiN catalyst was about 3.93, indicating that the ORR on the electrode was dominated by an efficient four-electron pathway. At the same time, the peroxide content was only 5%. The results of accelerated durability testing (ADT) showed that ALD-Pt/TiN had better ORR stability than Pt/C. This excellent electrocatalytic performance was probably due to the high dispersibility of the Pt nanoparticles deposited by ALD, good conductivity and corrosion resistance of TiN, and strong interactions between ALD-Pt and the TiN support. This work provides a reliable strategy for the design of new electrocatalytic materials with high activity and stability. Future research will focus on the strong interactions between ALD-Pt and the TiN carriers. ![]()
The exploitation of high-performing stable oxygen reduction reaction (ORR) electrocatalysts is critical for energy storage and conversion technologies. The existing high-efficiency electrocatalysts applied to the ORR are mainly based on Pt and its alloys. Moreover, carrier catalysts are the most widely used in actual electrocatalysis. A suitable carrier not only improves the utilization rate of precious metals and the service life of the catalyst, but also serves as a co-catalyst to ameliorate the catalytic activity through a synergistic effect in the reaction. Therefore, research into Pt-based electrocatalysts mainly focuses on the precious metal Pt and the carrier. With the aim of improving the activity and durability of Pt-based catalysts for the ORR, one-dimensional porous titanium nitride (TiN) nanotubes with a large specific surface area as well as good conductivity, electrochemical stability, and corrosion resistance were prepared in this study, and then, Pt nanoparticles were deposited on the TiN-support by atomic layer deposition (ALD). ALD is a novel and simple method for the preparation of films or nanoparticles with fine control of the thickness or size, respectively. The results of X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) experiments confirmed that the Pt nanoparticles obtained by ALD (ALD-Pt/TiN) were face-centered cubic (fcc) crystals with a uniform size and were highly dispersed on the surface of TiN. X-ray spectroscopy (XPS) measurements verified that the binding energy of Pt 4f in ALD-Pt/TiN was positively shifted by 0.33 eV with respect to that of the Pt/C catalyst, indicating strong electronic interactions between the ALD-Pt nanoparticles and the TiN carriers. Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) analyses revealed that ALD-Pt/TiN possessed high activity for the ORR and favorable durability. The onset potential and diffusion-limiting current density of ALD-Pt/TiN were similar to those of commercial Pt/C, while the half-wave potential was 20 mV higher than that of commercial Pt/C, indicating better electrocatalytic performance of the designed material. Furthermore, the electrocatalytic mechanism and kinetics for ALD-Pt/TiN were investigated by rotating ring-disc electrode (RRDE) experiments. The results suggested that the electron transfer number of the ALD-Pt/TiN catalyst was about 3.93, indicating that the ORR on the electrode was dominated by an efficient four-electron pathway. At the same time, the peroxide content was only 5%. The results of accelerated durability testing (ADT) showed that ALD-Pt/TiN had better ORR stability than Pt/C. This excellent electrocatalytic performance was probably due to the high dispersibility of the Pt nanoparticles deposited by ALD, good conductivity and corrosion resistance of TiN, and strong interactions between ALD-Pt and the TiN support. This work provides a reliable strategy for the design of new electrocatalytic materials with high activity and stability. Future research will focus on the strong interactions between ALD-Pt and the TiN carriers.
2020, 36(7): 191102
doi: 10.3866/PKU.WHXB201911025
Abstract:
2020, 36(7): 191201
doi: 10.3866/PKU.WHXB201912010
Abstract:
2020, 36(7): 191202
doi: 10.3866/PKU.WHXB201912023
Abstract:
2020, 36(7): 191203
doi: 10.3866/PKU.WHXB201912032
Abstract:
2020, 36(7): 191203
doi: 10.3866/PKU.WHXB201912039
Abstract:
2020, 36(7): 191205
doi: 10.3866/PKU.WHXB201912059
Abstract:
2020, 36(7): 200101
doi: 10.3866/PKU.WHXB202001011
Abstract:
2020, 36(7): 200101
doi: 10.3866/PKU.WHXB202001012
Abstract:
2020, 36(7): 200102
doi: 10.3866/PKU.WHXB202001022
Abstract:
2020, 36(7): 200101
doi: 10.3866/PKU.WHXB202001015
Abstract:
