Carbon supported gold-iridium composite(Au Ir/C) was synthesized by a facile one-step process and was investigated as the bifunctional catalyst for oxygen reduction reaction(ORR) and oxygen evolution reaction(OER). Th...Carbon supported gold-iridium composite(Au Ir/C) was synthesized by a facile one-step process and was investigated as the bifunctional catalyst for oxygen reduction reaction(ORR) and oxygen evolution reaction(OER). The physical properties of the Au Ir/C composite were characterized by transmission electron microscopy(TEM), X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS). Although the Au and Ir in the Au Ir/C did not form alloy, it is clear that the introduction of Ir decreases the average Au particle size to 4.2 nm compared to that in the Au/C(10.1 nm). By systematical analysis on chemical state of metal surface via XPS and the electrochemical results, it was found that the Au surface for the Au/C can be activated by potential cycling from 0.12 V to 1.72 V, resulting in the increased surface roughness of Au,thus improving the ORR activity. By the same potential cycling, the Ir surface of the Ir/C was irreversibly oxidized, leading to degraded ORR activity but uninfluenced OER activity. For the Au Ir/C, Ir protects Au against being oxidized due to the lower electronegativity of Ir. Combining the advantages of Au and Ir in catalyzing ORR and OER, the Au Ir/C catalyst displays an enhanced catalytic activity to the ORR and a comparable OER activity. In the 50-cycle accelerated aging test for the ORR and OER, the Au Ir/C displayed a satisfied stability, suggesting that the Au Ir/C catalyst is a potential bifunctional catalyst for the oxygen electrode.展开更多
N2O is a promising green propellant and exhibits great potential for satellite propulsion systems. It is difficult for catalytic decomposition, which is an important way to initiate the propulsion process, to occur at...N2O is a promising green propellant and exhibits great potential for satellite propulsion systems. It is difficult for catalytic decomposition, which is an important way to initiate the propulsion process, to occur at temperatures below 600 °C due to the high activation energy of N2O. In this work, we report an Ir supported on rutile TiO2（Ir/r-TiO2） catalyst which exhibits a fairly high activity for high-concentration N2O decomposition. HAADF-STEM, H2-TPR, and XPS results indicate that highly dispersed Ir particles and improved oxygen mobility on the Ir/r-TiO2 could facilitate the decompo-sition of N2O and desorption of the adsorbed oxygen. Bridge-bonded peroxide intermediates were observed with in-situ DRIFT and herein, a detailed decomposition route is proposed.展开更多
The widespread application of polymer electrolyte membrane water electrolyzers(PEMWEs)remains a tough challenge to date,as they rely on the use of highly scarce iridium(Ir)with insufficient catalytic performance for t...The widespread application of polymer electrolyte membrane water electrolyzers(PEMWEs)remains a tough challenge to date,as they rely on the use of highly scarce iridium(Ir)with insufficient catalytic performance for the oxygen evolution reaction(OER).Therefore,exploring the degradation and activation mechanism of Ir-based catalysts during the OER and searching for highly efficient Ir-based catalysts are essential to achieve large-scale hydrogen production with PEMWEs.This minireview briefly describes the adsorbate evolution mechanism and lattice oxygen oxidation mechanism for Ir-based catalysts to complete the OER process.Then,the valence change of Ir during the OER is discussed to illustrate the origin of the favorable stability of Ir-based catalysts.After that,different modification strategies for IrO2,such as elemental doping,surface engineering,atom utilization enhancing,and support engineering,are summarized in the hopes of finding some commonalities for improving performance.Finally,the perspectives for the development of Ir-based OER catalysts in PEMWEs are presented.展开更多
A termetallic catalyst of Pt-Ir-Au/Al2O3 for NOx decomposition was prepared by loading the metallic colloids in C2H5OH-H2O solution and a surfactant of polyvinyl pyrrolidone.Compared with an impregnated Pt/Al2O3 catal...A termetallic catalyst of Pt-Ir-Au/Al2O3 for NOx decomposition was prepared by loading the metallic colloids in C2H5OH-H2O solution and a surfactant of polyvinyl pyrrolidone.Compared with an impregnated Pt/Al2O3 catalyst,the termetallic catalyst of PtIrAu811/Al2O3,with a Pt：Ir：Au atomic ratio of 8：1：1,exhibited higher NO decomposition and selectivity to N2.Transmission electron microscopy and X-ray diffraction were conducted to clarify the state of the supported metals and indicate three precious metals alloyed on the catalyst.In the study of NO-temperature programmed desorption,oxygen desorption on the PtIrAu811 catalyst shifted to the low temperature side compared to that on Pt/Al2O3,which correlated well with its higher catalytic performance in NO decomposition.展开更多
Ir/ γ Al 2O 3 catalyst for hydrazine decomposition has been investigated by using XPS, SEM, H 2 TPD and H 2 isothermal adsorption. The results show that the iridium species enrich on the surface of the catalyst in mo...Ir/ γ Al 2O 3 catalyst for hydrazine decomposition has been investigated by using XPS, SEM, H 2 TPD and H 2 isothermal adsorption. The results show that the iridium species enrich on the surface of the catalyst in more than one state, and that the metallic iridium is the active sites for the reaction. The iridium species were sintered seriously during the reaction, and the amount of H 2 adsorption on used sample was only a quarter of that on fresh sample. The concentration of Cl - species on the surface decreased quickly at the initial period of the reaction process and stayed at a certain low value. Obvious breakup of the surface structure of the used sample was found. In all, the sintering of metallic iridium and the damage of alumina surface structure are the reasons for deactivation of the catalyst, while the Cl - concentration has little effect on the reaction performance.展开更多
基金financially supported by the Key Program of the Chinese Academy of Science(grant no.KGZD-EW-T08)the National Basic Research Program of China(973 Program,2012CB215500)the"Strategic Priority Research Program"of the Chinese Academy of Sciences(grant no.XDA09030104)
文摘Carbon supported gold-iridium composite(Au Ir/C) was synthesized by a facile one-step process and was investigated as the bifunctional catalyst for oxygen reduction reaction(ORR) and oxygen evolution reaction(OER). The physical properties of the Au Ir/C composite were characterized by transmission electron microscopy(TEM), X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS). Although the Au and Ir in the Au Ir/C did not form alloy, it is clear that the introduction of Ir decreases the average Au particle size to 4.2 nm compared to that in the Au/C(10.1 nm). By systematical analysis on chemical state of metal surface via XPS and the electrochemical results, it was found that the Au surface for the Au/C can be activated by potential cycling from 0.12 V to 1.72 V, resulting in the increased surface roughness of Au,thus improving the ORR activity. By the same potential cycling, the Ir surface of the Ir/C was irreversibly oxidized, leading to degraded ORR activity but uninfluenced OER activity. For the Au Ir/C, Ir protects Au against being oxidized due to the lower electronegativity of Ir. Combining the advantages of Au and Ir in catalyzing ORR and OER, the Au Ir/C catalyst displays an enhanced catalytic activity to the ORR and a comparable OER activity. In the 50-cycle accelerated aging test for the ORR and OER, the Au Ir/C displayed a satisfied stability, suggesting that the Au Ir/C catalyst is a potential bifunctional catalyst for the oxygen electrode.
基金supported by the National Natural Science Foundation of China (21476229, 21376236, 21503264)~~
文摘N2O is a promising green propellant and exhibits great potential for satellite propulsion systems. It is difficult for catalytic decomposition, which is an important way to initiate the propulsion process, to occur at temperatures below 600 °C due to the high activation energy of N2O. In this work, we report an Ir supported on rutile TiO2（Ir/r-TiO2） catalyst which exhibits a fairly high activity for high-concentration N2O decomposition. HAADF-STEM, H2-TPR, and XPS results indicate that highly dispersed Ir particles and improved oxygen mobility on the Ir/r-TiO2 could facilitate the decompo-sition of N2O and desorption of the adsorbed oxygen. Bridge-bonded peroxide intermediates were observed with in-situ DRIFT and herein, a detailed decomposition route is proposed.
基金This work was financially supported by the National Natural Science Foundation of China(22122202,22072051,and 21972051).
文摘The widespread application of polymer electrolyte membrane water electrolyzers(PEMWEs)remains a tough challenge to date,as they rely on the use of highly scarce iridium(Ir)with insufficient catalytic performance for the oxygen evolution reaction(OER).Therefore,exploring the degradation and activation mechanism of Ir-based catalysts during the OER and searching for highly efficient Ir-based catalysts are essential to achieve large-scale hydrogen production with PEMWEs.This minireview briefly describes the adsorbate evolution mechanism and lattice oxygen oxidation mechanism for Ir-based catalysts to complete the OER process.Then,the valence change of Ir during the OER is discussed to illustrate the origin of the favorable stability of Ir-based catalysts.After that,different modification strategies for IrO2,such as elemental doping,surface engineering,atom utilization enhancing,and support engineering,are summarized in the hopes of finding some commonalities for improving performance.Finally,the perspectives for the development of Ir-based OER catalysts in PEMWEs are presented.
文摘A termetallic catalyst of Pt-Ir-Au/Al2O3 for NOx decomposition was prepared by loading the metallic colloids in C2H5OH-H2O solution and a surfactant of polyvinyl pyrrolidone.Compared with an impregnated Pt/Al2O3 catalyst,the termetallic catalyst of PtIrAu811/Al2O3,with a Pt：Ir：Au atomic ratio of 8：1：1,exhibited higher NO decomposition and selectivity to N2.Transmission electron microscopy and X-ray diffraction were conducted to clarify the state of the supported metals and indicate three precious metals alloyed on the catalyst.In the study of NO-temperature programmed desorption,oxygen desorption on the PtIrAu811 catalyst shifted to the low temperature side compared to that on Pt/Al2O3,which correlated well with its higher catalytic performance in NO decomposition.
文摘Ir/ γ Al 2O 3 catalyst for hydrazine decomposition has been investigated by using XPS, SEM, H 2 TPD and H 2 isothermal adsorption. The results show that the iridium species enrich on the surface of the catalyst in more than one state, and that the metallic iridium is the active sites for the reaction. The iridium species were sintered seriously during the reaction, and the amount of H 2 adsorption on used sample was only a quarter of that on fresh sample. The concentration of Cl - species on the surface decreased quickly at the initial period of the reaction process and stayed at a certain low value. Obvious breakup of the surface structure of the used sample was found. In all, the sintering of metallic iridium and the damage of alumina surface structure are the reasons for deactivation of the catalyst, while the Cl - concentration has little effect on the reaction performance.
