The 5-parameter Morse potential （5-MP） of interaction between an adatom and metal surface cluster is put forward and performed on O-Pt stepped surface systems. We have primarily studied O/Pt（331）, O/Pt（221） and ...The 5-parameter Morse potential （5-MP） of interaction between an adatom and metal surface cluster is put forward and performed on O-Pt stepped surface systems. We have primarily studied O/Pt（331）, O/Pt（221） and O/Pt（553） systems and drawn some conclusions from the calculated results in good agreement with experimental and theoretical information. The O atom adsorbs stably near the step, so the step is the active place in the reaction. There are two types of atomic states, β1 and β2, in the adsorbed systems, corresponding to the three-fold states and four-fold long-bridged state behind the step respectively. Moreover, the length of （Ⅲ） terrace affects weakly the properties of all critical points in these systems.展开更多
Since the 1980s,single-crystal Pt electrodes with well-defined surface structures have been deemed stable under mild electrochemical conditions(e.g.,in the potential region of electric double layers,underpotential dep...Since the 1980s,single-crystal Pt electrodes with well-defined surface structures have been deemed stable under mild electrochemical conditions(e.g.,in the potential region of electric double layers,underpotential deposition of hydrogen,or mild hydrogen evolution/OH adsorption)and have served as model electrodes for unraveling the structure-performance relation in electrocatalysis.With the advancement of in situ electrochemical microscopy/spectroscopy techniques,subtle surface restructuring under mild electrochemical conditions has been achieved in the last decade.Surface restructuring can considerably modify electrocatalytic properties by generating/destroying highly active sites,thereby interfering with the deduction of the structure-performance relation.In this review,we summarize recent progress in the restructuring of well-defined Pt(-based)electrode surfaces under mild electrochemical conditions.The importance of the meticulous structural characterization of Pt electrodes before,during,and after electrochemical measurements is demonstrated using CO adsorption/oxidation,hydrogen adsorption/evolution,and oxygen reduction as examples.The implications of present findings for correctly identifying the reaction mechanisms and kinetics of other electrocatalytic systems are also briefly discussed.展开更多
We applied periodic density-functional theory to investigate the adsorption of HCN on x Ni@Pt（111） bimetallic surfaces（x = 1~4）. The results have been compared with those obtained on pure Ni（111） and Pt（111） s...We applied periodic density-functional theory to investigate the adsorption of HCN on x Ni@Pt（111） bimetallic surfaces（x = 1~4）. The results have been compared with those obtained on pure Ni（111） and Pt（111） surfaces. For all bimetallic surfaces,HCN is preferentially tilted with the CN bond parallel to the surface,and adsorption energies increase with an increasing number of layer Ni atoms on the surface. The adsorption energies of HCN on all bimetallic surfaces are larger than that on the Pt（111） surface,whereas the adsorption energies of HCN on 3Ni@Pt（111） and 4Ni@Pt（111） are larger than that on the Ni（111） surface,indicating that the introduction of Ni to the Pt catalyst could increase the activity of bimetallic catalyst in the hydrogenation reaction for nitriles. Larger adsorption energy of HCN leads to a longer C–N bond length and a smaller CN vibrational frequency. The analysis of Bader charge and vibrational frequencies showed obvious weakening of the adsorbed C–N bond and an indication of sp2 hybridization of both carbon and nitrogen atoms.展开更多
Alloying and nanostructuring are two strategies used to facilitate the efficient electrocatalysis of the oxygen reduction reaction(ORR)by Pt,where the high index surfaces(HISs)of Pt exhibit superior activity for ORR.H...Alloying and nanostructuring are two strategies used to facilitate the efficient electrocatalysis of the oxygen reduction reaction(ORR)by Pt,where the high index surfaces(HISs)of Pt exhibit superior activity for ORR.Here,we report the fabrication of PtCu3 nanodendrites possessing rich spiny branches exposing n(111)×(110)HISs.The dendrites were formed through an etching‐modulated seeding and growing strategy.Specifically,an oxidative atmosphere was initially applied to form the concaved nanocubes of the Pt‐Cu seeds,which was then switched to an inert atmosphere to promote an explosive growth of dendrites.Separately,the oxidative or inert atmosphere failed to produce this hyperbranched structure.Electrochemical dealloying of the PtCu3 nanodendrites produced Pt3Cu shells with Pt‐rich surfaces where HIS‐exposed dendrite structures were maintained.The resulting PtCu_(3)@Pt_(3)Cu@Pt nanodendrites in 0.1 M HClO4 exhibited excellent mass and area specific activities for ORR,which were 14 and 24 times higher than that of commercial Pt/C,respectively.DFT calculations revealed that Cu alloying and HISs both contributed to the significantly enhanced activity of Pt,and that the oxygen binding energy on the step sites of HISs on the PtCu_(3)@Pt_(3)Cu@Pt nanodendrites approached the optimal value to achieve a near peak‐top ORR activity.展开更多
Using first-principles calculations, we studied the interaction of methanol with the Pt（100） surface based on generalized gradient approximation. We found that top sites of Pt（100） surface are the favored adsorpti...Using first-principles calculations, we studied the interaction of methanol with the Pt（100） surface based on generalized gradient approximation. We found that top sites of Pt（100） surface are the favored adsorptive positions in energy, and methanol molecule interacts with the Pt surface through oxygen atoms. Moreover, we also explored the possible dissociation pathways of methanol on the Pt surface, and suggested that the products of dissociation can be controlled by the external manipulation.展开更多
The magnetism and surface behaviour of Pt-Dy/γ-Al_2O_3 catalysts were studied respectively by means of a Faraday magnetic balance and the method of carbon disulfide.The ferromagnetic impurity in the support,γ-Al_2O_...The magnetism and surface behaviour of Pt-Dy/γ-Al_2O_3 catalysts were studied respectively by means of a Faraday magnetic balance and the method of carbon disulfide.The ferromagnetic impurity in the support,γ-Al_2O_3,at low temperature was corrected for the first time.The magnetic susceptibilities of the cat- alysts follow the sequence in different stage of preparation:χ_(uncalcined)<χ_(calcined)<χ_(reduced). The magnetic susceptibilities of the catalysts decrease as they adsorb hydrogen,cyclohexane or benzene. There is a correlation between the aromatization yield of cyclohexane or heptane on these catalysts and the magnetic susceptibility of the catalysts.Since addition of Dy increases the number of adsorption sites and the relevant proportions of weak adsorption sites,the abilities of sulfur-resistance and cyclohexane dehydrogenation are improved.In Pt-Dy/γ-A:_2O_3 catalysts,Dy improves the aromatization activity and stability of the catalyst and plays the role of the electron promoter.展开更多
The density functional theory（DFT） and self-consistent periodic calculation were used to investigate the methanol adsorption on the Pt-Mo（111）/C surface.The adsorption energies,equilibrium geometries and vibration...The density functional theory（DFT） and self-consistent periodic calculation were used to investigate the methanol adsorption on the Pt-Mo（111）/C surface.The adsorption energies,equilibrium geometries and vibration frequencies of CH3OH on nine types of sites on the Pt-Mo（111）/C surface were predicted and the favorite adsorption site for methanol is the top-Pt site.Both sites of valence and conduction bands of doped system have been broadened,which are favorable for electrons to transfer to the cavity.The possible decomposition pathway was investigated with transition state searching and the calculation results indicate that the O-H bond is first broken,and then the methanol decomposes into methoxy.The activation barrier of O-H bond breaking with Pt-Mo catalyst is only 104.8 kJ mol-1,showing that carbon supported Pt-Mo alloys have promoted the decomposition of methanol.Comparing with the adsorption energies of CH3OH on the Pt（111）/C surface and that of CO,the adsorption energies of CO are higher,and Pt（111）/C is liable to be oxidized and loses the activity,which suggests that the catalyst Pt-Mo（111）/C is in favor of decomposing methanol and has better anti-poisoning ability than Pt（111）/C.展开更多
The 5-parameter Morse potential （5-MP） of the interaction between H atom and Ag surfaces has been constructed. The adsorption and diffusion of H on Ag low-index surfaces are investigated with 5-MP in detail. The cha...The 5-parameter Morse potential （5-MP） of the interaction between H atom and Ag surfaces has been constructed. The adsorption and diffusion of H on Ag low-index surfaces are investigated with 5-MP in detail. The characteristics of critical points are obtained. The theoretical results show that H atom can only adsorb at the three-fold site on Ag（111 ）; the quasi-3-fold site and long-bridge site are stable adsorption sites on Ag（110） surface for the H atom, and at low coverage hydrogen predominantly occupies the quasi-3-fold site. This work predicts that the four-fold hollow site is the most stable adsorption state for H atom on Ag（100）. The results of this work are approved by the experimental and theoretical results.展开更多
The adsorption of CH3CN and CH3NC on the Pt（lll） surface at the 1/4 monolayer （ML） coverage has been car-ried out at the level of density functional theory for understanding hydrogenation processes of nitriles. Th...The adsorption of CH3CN and CH3NC on the Pt（lll） surface at the 1/4 monolayer （ML） coverage has been car-ried out at the level of density functional theory for understanding hydrogenation processes of nitriles. The most favored ad-sorption structure for CH3 CN is the C--N bond almost parallel to the surface with the C-N bond interaction with adjacent surface Pt atoms. For CH3NC, the most stable configuration is the CH3 NC locates at the face center cubic （fcc） site with the C-atom bonded to three Pt atoms. In addition, the HCN and HNC adsorption has been computed, and the adsorption pattern is nearly similar to the CH3CN and CH3NC, respectively. The adsorbed molecules rehybridize on the surface, be-coming non-linear with a bent C-C-N or C-N-C angle. Furthermore, the binding mechanism of these molecules on the Pt（111） surface is also analyzed.展开更多
An analysis of the molecular dynamics of ethanol solvated by water molecules in the absence and presence of a Pt surface has been performed using DL_POLY_2.19 code. The structure and diffusion properties of an ethanol...An analysis of the molecular dynamics of ethanol solvated by water molecules in the absence and presence of a Pt surface has been performed using DL_POLY_2.19 code. The structure and diffusion properties of an ethanol–water system have been studied at various temperatures from 250 to 600 K. We have measured the self-diffusion coefficients of the 50:50% ethanol–water solution;in the absence of a Pt surface our results show an excellent agreement–within an error of 7.4% – with the experimental data. An increase in the self-diffusion coefficients with the inclusion of a Pt surface has been observed. The estimation of the diffusion coefficients of both water and ethanol in the presence of a Pt surface shows that they obey the Arrhenius equation;the calculated activation energies of diffusion of ethanol and water are 2.47 and 2.98 Kcal/mole, respectively. The radial distribution function graphs and density profiles have been built;their correlations with the self-diffusion coefficients of both ethanol and water molecules are also illustrated.展开更多
In this work we have performed total-energy calculations of the chemisorption properties and STM images of Pt (111) ( × )R30°/CO Surface;STM Image;ChemisorptionR30°/CO surface by using the density funct...In this work we have performed total-energy calculations of the chemisorption properties and STM images of Pt (111) ( × )R30°/CO Surface;STM Image;ChemisorptionR30°/CO surface by using the density functional theory (DFT) and the projector-augmented wave (PAW) method. The calculations show that carbon monoxide molecule (CO) adsorbs on FCC site in the Pt (111) ( × )R30°/ surface is energetically favored by the GGA-PBE XC-functional, this is in agreement with most of the theoretical calculations which is using different XC-functional at the most. However, these results strongly conflicted with the existing experiments. Actually the calculated work function for the FCC adsorption is quite different from the experiments while the atop one is in good agreement with experiments. We speculate that the atop adsorption for (CO is favorable for the adsorption case at the most. Furthermore, we have calculated the scanning tunneling microscopy (STM) images for both adsorption geometries and suggest that there should be existed remarkable differences in the STM images. The present work provides a faithful criterion accounting for the local surface geometry in Pt (111) ( × )R30°/CO surface from surface work functions and STM images instead of totalenergy calculations.展开更多
质子交换膜燃料电池(PEMFCs)将化学燃料转化为电能,具有能量转换效率高、清洁、零排放等特点,被认为是未来重要的能源利用装置.与阳极发生的氢氧化反应相比,阴极发生的氧还原反应(ORR)是动力学缓慢的过程,严重阻碍了燃料电池的广泛应用...质子交换膜燃料电池(PEMFCs)将化学燃料转化为电能,具有能量转换效率高、清洁、零排放等特点,被认为是未来重要的能源利用装置.与阳极发生的氢氧化反应相比,阴极发生的氧还原反应(ORR)是动力学缓慢的过程,严重阻碍了燃料电池的广泛应用,因此迫切需要开发高活性的电催化剂来降低其电化学过电位,提高反应动力学.铂基纳米晶是氧还原反应有效的电催化剂,但存在成本高、储量少且耐用性差等问题.将铂(Pt)与过渡金属(Fe,Co,Ni等)合金化可以提升催化活性,且最外层有序的Pt原子层可以有效地避免过渡金属的腐蚀溶解,同时,利用金(Au)与Pt基合金形成核壳结构可以有效地降低催化剂成本,同时增强稳定性.然而,在以Au作为核时,很难通过退火处理获得富含Pt层的核壳催化剂.本文利用钛(Ti)原子与Au原子合金化后的协同作用,成功地制备了核壳AuTi@PtNi氧还原催化剂.由于Ti与Au的强相互作用,使得该催化剂即使经高温退火处理,依旧可以使Au保持在内部,同时可以获得富Pt壳层.利用配备有电子能量损失谱的透射电子显微镜及X射线电子能谱对催化剂进行表征,结果表明,Ti的引入可大大提升催化剂的热稳定性.由于具有核壳结构及富Pt的PtNi壳层,退火后的AuTi@PtNi-400催化剂在0.9 V(RHE)时的质量比活性(5.26 A mgPt^(‒1))和面积比活性(2.72 mA cm^(‒2))分别是商业化Pt/C催化剂的19.26倍和9.84倍.另外,AuTi@PtNi-400催化剂在20000圈循环测试后质量活性衰减不到10%,稳定性好于商业化Pt/C催化剂和未经过退火的AuTi@PtNi催化剂.进一步对AuTi@PtNi-400进行电催化测试,结果表明,在功率密度达到0.61 W cm^(‒2)的同时可产生1.31 A cm^(‒2)的电流密度,该结果优于商业化Pt(1.05 A cm^(‒2)和0.34 W cm^(‒2))以及Ti-Au@PtNi/C(1.25 A cm^(‒2)和0.62 W cm^(‒2)),峰值功率密度高达0.80 W cm^(‒2),这表明所制备的Ti-Au@PtNi/C-400催化剂不仅在三电极体系中具有较好的性能,在电堆测试中也展现出高性能,可以较大地满足和促进燃料电池的发展和应用.综上所述,对于燃料电池阴极催化剂,可结合形貌工程及协调作用,制备出低成本高性能的ORR催化剂,为燃料电池的进一步应用提供新思路.展开更多
The experimental research programs of 1950s, to understand the adsorption of CO on W surfaces, changed to ab initio studies in 2000s. The goals were to seek improved practical applications. Most of the studies were ba...The experimental research programs of 1950s, to understand the adsorption of CO on W surfaces, changed to ab initio studies in 2000s. The goals were to seek improved practical applications. Most of the studies were based on density functional theory. Many studies also used programs, such as VASP (Vienna Abinitio simulation package) and CPMD. The computational procedures used plane wave approximations. This needed studies with selection of K points and cutoff energy selection to assure convergence in energy calculations. Observations and analysis of papers published from 2006 to 2022 indicate that the cutoff energies were selected arbitrarily without any needed convergence studies. By selecting a published 2006 paper, this paper has clearly showed that an arbitrary selection of cutoff energy, such as 460 eV, is not in the range of, cutoff energies that assure convergence of energy calculations, with ab initio methods and have indicated correction procedures. .展开更多
基金The project was supported by NSF of Shandong Province (Y2002B09)
文摘The 5-parameter Morse potential （5-MP） of interaction between an adatom and metal surface cluster is put forward and performed on O-Pt stepped surface systems. We have primarily studied O/Pt（331）, O/Pt（221） and O/Pt（553） systems and drawn some conclusions from the calculated results in good agreement with experimental and theoretical information. The O atom adsorbs stably near the step, so the step is the active place in the reaction. There are two types of atomic states, β1 and β2, in the adsorbed systems, corresponding to the three-fold states and four-fold long-bridged state behind the step respectively. Moreover, the length of （Ⅲ） terrace affects weakly the properties of all critical points in these systems.
文摘Since the 1980s,single-crystal Pt electrodes with well-defined surface structures have been deemed stable under mild electrochemical conditions(e.g.,in the potential region of electric double layers,underpotential deposition of hydrogen,or mild hydrogen evolution/OH adsorption)and have served as model electrodes for unraveling the structure-performance relation in electrocatalysis.With the advancement of in situ electrochemical microscopy/spectroscopy techniques,subtle surface restructuring under mild electrochemical conditions has been achieved in the last decade.Surface restructuring can considerably modify electrocatalytic properties by generating/destroying highly active sites,thereby interfering with the deduction of the structure-performance relation.In this review,we summarize recent progress in the restructuring of well-defined Pt(-based)electrode surfaces under mild electrochemical conditions.The importance of the meticulous structural characterization of Pt electrodes before,during,and after electrochemical measurements is demonstrated using CO adsorption/oxidation,hydrogen adsorption/evolution,and oxygen reduction as examples.The implications of present findings for correctly identifying the reaction mechanisms and kinetics of other electrocatalytic systems are also briefly discussed.
基金supported by the National Natural Science Foundation of China(21203027,21373048,21371034)Scientific Development Fund of Fuzhou University(2012-XQ-11)
文摘We applied periodic density-functional theory to investigate the adsorption of HCN on x Ni@Pt（111） bimetallic surfaces（x = 1~4）. The results have been compared with those obtained on pure Ni（111） and Pt（111） surfaces. For all bimetallic surfaces,HCN is preferentially tilted with the CN bond parallel to the surface,and adsorption energies increase with an increasing number of layer Ni atoms on the surface. The adsorption energies of HCN on all bimetallic surfaces are larger than that on the Pt（111） surface,whereas the adsorption energies of HCN on 3Ni@Pt（111） and 4Ni@Pt（111） are larger than that on the Ni（111） surface,indicating that the introduction of Ni to the Pt catalyst could increase the activity of bimetallic catalyst in the hydrogenation reaction for nitriles. Larger adsorption energy of HCN leads to a longer C–N bond length and a smaller CN vibrational frequency. The analysis of Bader charge and vibrational frequencies showed obvious weakening of the adsorbed C–N bond and an indication of sp2 hybridization of both carbon and nitrogen atoms.
文摘Alloying and nanostructuring are two strategies used to facilitate the efficient electrocatalysis of the oxygen reduction reaction(ORR)by Pt,where the high index surfaces(HISs)of Pt exhibit superior activity for ORR.Here,we report the fabrication of PtCu3 nanodendrites possessing rich spiny branches exposing n(111)×(110)HISs.The dendrites were formed through an etching‐modulated seeding and growing strategy.Specifically,an oxidative atmosphere was initially applied to form the concaved nanocubes of the Pt‐Cu seeds,which was then switched to an inert atmosphere to promote an explosive growth of dendrites.Separately,the oxidative or inert atmosphere failed to produce this hyperbranched structure.Electrochemical dealloying of the PtCu3 nanodendrites produced Pt3Cu shells with Pt‐rich surfaces where HIS‐exposed dendrite structures were maintained.The resulting PtCu_(3)@Pt_(3)Cu@Pt nanodendrites in 0.1 M HClO4 exhibited excellent mass and area specific activities for ORR,which were 14 and 24 times higher than that of commercial Pt/C,respectively.DFT calculations revealed that Cu alloying and HISs both contributed to the significantly enhanced activity of Pt,and that the oxygen binding energy on the step sites of HISs on the PtCu_(3)@Pt_(3)Cu@Pt nanodendrites approached the optimal value to achieve a near peak‐top ORR activity.
文摘Using first-principles calculations, we studied the interaction of methanol with the Pt（100） surface based on generalized gradient approximation. We found that top sites of Pt（100） surface are the favored adsorptive positions in energy, and methanol molecule interacts with the Pt surface through oxygen atoms. Moreover, we also explored the possible dissociation pathways of methanol on the Pt surface, and suggested that the products of dissociation can be controlled by the external manipulation.
文摘The magnetism and surface behaviour of Pt-Dy/γ-Al_2O_3 catalysts were studied respectively by means of a Faraday magnetic balance and the method of carbon disulfide.The ferromagnetic impurity in the support,γ-Al_2O_3,at low temperature was corrected for the first time.The magnetic susceptibilities of the cat- alysts follow the sequence in different stage of preparation:χ_(uncalcined)<χ_(calcined)<χ_(reduced). The magnetic susceptibilities of the catalysts decrease as they adsorb hydrogen,cyclohexane or benzene. There is a correlation between the aromatization yield of cyclohexane or heptane on these catalysts and the magnetic susceptibility of the catalysts.Since addition of Dy increases the number of adsorption sites and the relevant proportions of weak adsorption sites,the abilities of sulfur-resistance and cyclohexane dehydrogenation are improved.In Pt-Dy/γ-A:_2O_3 catalysts,Dy improves the aromatization activity and stability of the catalyst and plays the role of the electron promoter.
文摘The density functional theory（DFT） and self-consistent periodic calculation were used to investigate the methanol adsorption on the Pt-Mo（111）/C surface.The adsorption energies,equilibrium geometries and vibration frequencies of CH3OH on nine types of sites on the Pt-Mo（111）/C surface were predicted and the favorite adsorption site for methanol is the top-Pt site.Both sites of valence and conduction bands of doped system have been broadened,which are favorable for electrons to transfer to the cavity.The possible decomposition pathway was investigated with transition state searching and the calculation results indicate that the O-H bond is first broken,and then the methanol decomposes into methoxy.The activation barrier of O-H bond breaking with Pt-Mo catalyst is only 104.8 kJ mol-1,showing that carbon supported Pt-Mo alloys have promoted the decomposition of methanol.Comparing with the adsorption energies of CH3OH on the Pt（111）/C surface and that of CO,the adsorption energies of CO are higher,and Pt（111）/C is liable to be oxidized and loses the activity,which suggests that the catalyst Pt-Mo（111）/C is in favor of decomposing methanol and has better anti-poisoning ability than Pt（111）/C.
基金The project was supported by NSF of Shandong Province (Y2002B09)
文摘The 5-parameter Morse potential （5-MP） of the interaction between H atom and Ag surfaces has been constructed. The adsorption and diffusion of H on Ag low-index surfaces are investigated with 5-MP in detail. The characteristics of critical points are obtained. The theoretical results show that H atom can only adsorb at the three-fold site on Ag（111 ）; the quasi-3-fold site and long-bridge site are stable adsorption sites on Ag（110） surface for the H atom, and at low coverage hydrogen predominantly occupies the quasi-3-fold site. This work predicts that the four-fold hollow site is the most stable adsorption state for H atom on Ag（100）. The results of this work are approved by the experimental and theoretical results.
基金Natural Science Foundation of Shanxi Province(No. 2009011014)
文摘The adsorption of CH3CN and CH3NC on the Pt（lll） surface at the 1/4 monolayer （ML） coverage has been car-ried out at the level of density functional theory for understanding hydrogenation processes of nitriles. The most favored ad-sorption structure for CH3 CN is the C--N bond almost parallel to the surface with the C-N bond interaction with adjacent surface Pt atoms. For CH3NC, the most stable configuration is the CH3 NC locates at the face center cubic （fcc） site with the C-atom bonded to three Pt atoms. In addition, the HCN and HNC adsorption has been computed, and the adsorption pattern is nearly similar to the CH3CN and CH3NC, respectively. The adsorbed molecules rehybridize on the surface, be-coming non-linear with a bent C-C-N or C-N-C angle. Furthermore, the binding mechanism of these molecules on the Pt（111） surface is also analyzed.
文摘An analysis of the molecular dynamics of ethanol solvated by water molecules in the absence and presence of a Pt surface has been performed using DL_POLY_2.19 code. The structure and diffusion properties of an ethanol–water system have been studied at various temperatures from 250 to 600 K. We have measured the self-diffusion coefficients of the 50:50% ethanol–water solution;in the absence of a Pt surface our results show an excellent agreement–within an error of 7.4% – with the experimental data. An increase in the self-diffusion coefficients with the inclusion of a Pt surface has been observed. The estimation of the diffusion coefficients of both water and ethanol in the presence of a Pt surface shows that they obey the Arrhenius equation;the calculated activation energies of diffusion of ethanol and water are 2.47 and 2.98 Kcal/mole, respectively. The radial distribution function graphs and density profiles have been built;their correlations with the self-diffusion coefficients of both ethanol and water molecules are also illustrated.
文摘In this work we have performed total-energy calculations of the chemisorption properties and STM images of Pt (111) ( × )R30°/CO Surface;STM Image;ChemisorptionR30°/CO surface by using the density functional theory (DFT) and the projector-augmented wave (PAW) method. The calculations show that carbon monoxide molecule (CO) adsorbs on FCC site in the Pt (111) ( × )R30°/ surface is energetically favored by the GGA-PBE XC-functional, this is in agreement with most of the theoretical calculations which is using different XC-functional at the most. However, these results strongly conflicted with the existing experiments. Actually the calculated work function for the FCC adsorption is quite different from the experiments while the atop one is in good agreement with experiments. We speculate that the atop adsorption for (CO is favorable for the adsorption case at the most. Furthermore, we have calculated the scanning tunneling microscopy (STM) images for both adsorption geometries and suggest that there should be existed remarkable differences in the STM images. The present work provides a faithful criterion accounting for the local surface geometry in Pt (111) ( × )R30°/CO surface from surface work functions and STM images instead of totalenergy calculations.
文摘质子交换膜燃料电池(PEMFCs)将化学燃料转化为电能,具有能量转换效率高、清洁、零排放等特点,被认为是未来重要的能源利用装置.与阳极发生的氢氧化反应相比,阴极发生的氧还原反应(ORR)是动力学缓慢的过程,严重阻碍了燃料电池的广泛应用,因此迫切需要开发高活性的电催化剂来降低其电化学过电位,提高反应动力学.铂基纳米晶是氧还原反应有效的电催化剂,但存在成本高、储量少且耐用性差等问题.将铂(Pt)与过渡金属(Fe,Co,Ni等)合金化可以提升催化活性,且最外层有序的Pt原子层可以有效地避免过渡金属的腐蚀溶解,同时,利用金(Au)与Pt基合金形成核壳结构可以有效地降低催化剂成本,同时增强稳定性.然而,在以Au作为核时,很难通过退火处理获得富含Pt层的核壳催化剂.本文利用钛(Ti)原子与Au原子合金化后的协同作用,成功地制备了核壳AuTi@PtNi氧还原催化剂.由于Ti与Au的强相互作用,使得该催化剂即使经高温退火处理,依旧可以使Au保持在内部,同时可以获得富Pt壳层.利用配备有电子能量损失谱的透射电子显微镜及X射线电子能谱对催化剂进行表征,结果表明,Ti的引入可大大提升催化剂的热稳定性.由于具有核壳结构及富Pt的PtNi壳层,退火后的AuTi@PtNi-400催化剂在0.9 V(RHE)时的质量比活性(5.26 A mgPt^(‒1))和面积比活性(2.72 mA cm^(‒2))分别是商业化Pt/C催化剂的19.26倍和9.84倍.另外,AuTi@PtNi-400催化剂在20000圈循环测试后质量活性衰减不到10%,稳定性好于商业化Pt/C催化剂和未经过退火的AuTi@PtNi催化剂.进一步对AuTi@PtNi-400进行电催化测试,结果表明,在功率密度达到0.61 W cm^(‒2)的同时可产生1.31 A cm^(‒2)的电流密度,该结果优于商业化Pt(1.05 A cm^(‒2)和0.34 W cm^(‒2))以及Ti-Au@PtNi/C(1.25 A cm^(‒2)和0.62 W cm^(‒2)),峰值功率密度高达0.80 W cm^(‒2),这表明所制备的Ti-Au@PtNi/C-400催化剂不仅在三电极体系中具有较好的性能,在电堆测试中也展现出高性能,可以较大地满足和促进燃料电池的发展和应用.综上所述,对于燃料电池阴极催化剂,可结合形貌工程及协调作用,制备出低成本高性能的ORR催化剂,为燃料电池的进一步应用提供新思路.
文摘The experimental research programs of 1950s, to understand the adsorption of CO on W surfaces, changed to ab initio studies in 2000s. The goals were to seek improved practical applications. Most of the studies were based on density functional theory. Many studies also used programs, such as VASP (Vienna Abinitio simulation package) and CPMD. The computational procedures used plane wave approximations. This needed studies with selection of K points and cutoff energy selection to assure convergence in energy calculations. Observations and analysis of papers published from 2006 to 2022 indicate that the cutoff energies were selected arbitrarily without any needed convergence studies. By selecting a published 2006 paper, this paper has clearly showed that an arbitrary selection of cutoff energy, such as 460 eV, is not in the range of, cutoff energies that assure convergence of energy calculations, with ab initio methods and have indicated correction procedures. .
