通过电解水制备氢气是实现“碳中和”目标的理想途径之一.因此,可在全p H条件下使用的氢析出(HER)催化剂的研发是近年来电催化领域的研究热点.原子级分散的催化剂,能够在保留铂族金属(PGM)固有活性的同时,降低催化剂中PGM的用量.虽然可...通过电解水制备氢气是实现“碳中和”目标的理想途径之一.因此,可在全p H条件下使用的氢析出(HER)催化剂的研发是近年来电催化领域的研究热点.原子级分散的催化剂,能够在保留铂族金属(PGM)固有活性的同时,降低催化剂中PGM的用量.虽然可以通过X射线吸收光谱(XAS)来表征原子分散的PGM电催化剂的配位环境,但目前对原子空间分布的控制仍然具有挑战.本文制备了钒掺杂钨青铜内通道氨配位的钌单原子催化剂(Ru/V-NHWO),用于全p H范围内的HER反应.采用X射线衍射(XRD)、高角环形暗场扫描透射电镜(HAADF-STEM)、X射线光电子能谱(XPS)和原位X射线吸收光谱(XAS)等进行表征,研究了钌单原子与V-NHWO载体的结合方式以及构效关系,并采用密度泛函理论(DFT)计算探索了催化剂中诸多位点的活性贡献.在1 mol/LKOH, 0.5 mol/L H_(2)SO_(4)和1 mol/L磷酸盐缓冲溶液中,其在10 m Acm^(-2)下的过电位分别为28.0, 29.6和40.6 m V.同时,在过电位100 m V时,质量活性分别达到3930, 1941和602.8 m Amg^(-1)Ru,数倍于同等条件下的商业铂碳.XRD结果表明,钌的引入可以确保催化剂在氩气条件下热解后仍保持六方钨铵青铜晶相,证明钌与钨铵青铜六方晶体通道内氨物种,即“通道氨”的结合.HAADF-STEM结果表明,钌原子与NHWO间存在强烈相互作用,有助于提升HER性能.XPS和XAS结果表明, W5+信号出现在引入钌后,峰位置的结合能增加且峰面积降低,说明钌与通道氨之间存在相互作用.N的XPS结果表明,钌的引入导致了金属氨键的形成.XAS结果表明, Ru/V-NHWO/CC中钌单原子和钌团簇共存,钌单原子与通道氨配位,并且钒的引入会诱发V-NHWO中金属键长缩短,这表明催化剂的金属性得到了提升,有利于改善其导电性.采用DFT计算进一步研究了HER活性的来源.相比于V-NHWO载体和钌团簇修饰的V-NHWO,以单原子形式结合的钌具有更低的水解离能垒,该能垒在氨桥接的钌双原子垂直插入、钒掺杂和多通道插入等多种因素作用下进一步降低.同时,氢中间体结合能得到了相应的优化而趋近于0 e V.此外,差分电荷密度模拟结果表明,氢中间体结合后, V-NHWO对于钌单原子存在明显的供电子行为,有利于HER动力学过程.综上,本工作报道了金属载体对于高分散金属原子空间分布调控的重要作用,可为设计和构筑可应用于诸多能源转换过程的新型原子级分散催化剂提供参考.展开更多
Decay of the energy for the Cauchy problem of the wave equation of variable coefficients with a dissipation is considered. It is shown that whether a dissipation can be localized near infinity depends on the curvature...Decay of the energy for the Cauchy problem of the wave equation of variable coefficients with a dissipation is considered. It is shown that whether a dissipation can be localized near infinity depends on the curvature properties of a Riemannian metric given by the variable coefficients. In particular, some criteria on curvature of the Riemannian manifold for a dissipation to be localized are given.展开更多
The discovery of single-atom catalysts(SACs)represents a groundbreaking advancement in the field of catalysis over the past decades.With the in-depth exploration of relevant structure-activity relationships,the metal−...The discovery of single-atom catalysts(SACs)represents a groundbreaking advancement in the field of catalysis over the past decades.With the in-depth exploration of relevant structure-activity relationships,the metal−support interaction(MSI)is widely adopted to elucidate variations in electronic structure and coordination configuration of atomic active sites on various kinds of supports.Herein,we briefly summarize the metal oxide supports for SACs fabrication,including the distinctive characteristics of metal oxide supports,enlightening advancements in metal oxide support-based SACs(MO-SACs),feasible preparation methods for MO-SACs and effective regulation strategies of MSI effect in MO-SACs.In addition,we present our viewpoints and outlook in this field to stimulate rational design and construction of novel MO-SACs applied in diverse renewable energy devices,while some universal suggestions are sincerely given to provoke thoughtful considerations during the research process.展开更多
This paper considers the existence of global smooth solutions of semilinear schrSdinger equation with a boundary feedback on 2-dimensional Riemannian manifolds when initial data are small. The authors show that the ex...This paper considers the existence of global smooth solutions of semilinear schrSdinger equation with a boundary feedback on 2-dimensional Riemannian manifolds when initial data are small. The authors show that the existence of global solutions depends not only on the boundary feedback, but also on a Riemannian metric, given by the coefficient of the principle part and the original metric of the manifold. In particular, the authers prove that the energy of the system decays exponentially.展开更多
This paper analyses harmonic distortion caused by the narrow pulse problem in matrix converters,and presents an improved switching pattern that is based on the basic five vector switching pattern.With limited switchin...This paper analyses harmonic distortion caused by the narrow pulse problem in matrix converters,and presents an improved switching pattern that is based on the basic five vector switching pattern.With limited switching frequencies,the improved pattern solves the narrow pulse problem by applying an additional zero vector and adjusting the sequence of the four active vectors at the same time to minimize the switching times.Simulation results show that in the six vector switching pattern,a)the low-frequency harmonics caused by the narrow pulse problem are greatly reduced;b)the average switching frequency is reduced compared with the five vector pattern;c)the sampling frequency harmonics are apparently attenuated though a little 1/2 and 3/2 sampling frequency harmonics are produced;d)the THD of the output current is improved to the same level of the three zero vector switching pattern(TZVSP);e)the proposed switching pattern has benefits in both normal and unbalance input voltage conditions.Experimental results on a matrix converter platform,verify the benefits of the six vector switching pattern.Faster dynamic,lower harmonics and lower losses can be achieved by using the proposed six vector switching pattern.展开更多
文摘通过电解水制备氢气是实现“碳中和”目标的理想途径之一.因此,可在全p H条件下使用的氢析出(HER)催化剂的研发是近年来电催化领域的研究热点.原子级分散的催化剂,能够在保留铂族金属(PGM)固有活性的同时,降低催化剂中PGM的用量.虽然可以通过X射线吸收光谱(XAS)来表征原子分散的PGM电催化剂的配位环境,但目前对原子空间分布的控制仍然具有挑战.本文制备了钒掺杂钨青铜内通道氨配位的钌单原子催化剂(Ru/V-NHWO),用于全p H范围内的HER反应.采用X射线衍射(XRD)、高角环形暗场扫描透射电镜(HAADF-STEM)、X射线光电子能谱(XPS)和原位X射线吸收光谱(XAS)等进行表征,研究了钌单原子与V-NHWO载体的结合方式以及构效关系,并采用密度泛函理论(DFT)计算探索了催化剂中诸多位点的活性贡献.在1 mol/LKOH, 0.5 mol/L H_(2)SO_(4)和1 mol/L磷酸盐缓冲溶液中,其在10 m Acm^(-2)下的过电位分别为28.0, 29.6和40.6 m V.同时,在过电位100 m V时,质量活性分别达到3930, 1941和602.8 m Amg^(-1)Ru,数倍于同等条件下的商业铂碳.XRD结果表明,钌的引入可以确保催化剂在氩气条件下热解后仍保持六方钨铵青铜晶相,证明钌与钨铵青铜六方晶体通道内氨物种,即“通道氨”的结合.HAADF-STEM结果表明,钌原子与NHWO间存在强烈相互作用,有助于提升HER性能.XPS和XAS结果表明, W5+信号出现在引入钌后,峰位置的结合能增加且峰面积降低,说明钌与通道氨之间存在相互作用.N的XPS结果表明,钌的引入导致了金属氨键的形成.XAS结果表明, Ru/V-NHWO/CC中钌单原子和钌团簇共存,钌单原子与通道氨配位,并且钒的引入会诱发V-NHWO中金属键长缩短,这表明催化剂的金属性得到了提升,有利于改善其导电性.采用DFT计算进一步研究了HER活性的来源.相比于V-NHWO载体和钌团簇修饰的V-NHWO,以单原子形式结合的钌具有更低的水解离能垒,该能垒在氨桥接的钌双原子垂直插入、钒掺杂和多通道插入等多种因素作用下进一步降低.同时,氢中间体结合能得到了相应的优化而趋近于0 e V.此外,差分电荷密度模拟结果表明,氢中间体结合后, V-NHWO对于钌单原子存在明显的供电子行为,有利于HER动力学过程.综上,本工作报道了金属载体对于高分散金属原子空间分布调控的重要作用,可为设计和构筑可应用于诸多能源转换过程的新型原子级分散催化剂提供参考.
基金supported by the National Natural Science Foundation of China (Nos.60225003,60821091,10831007,60774025)KJCX3-SYW-S01
文摘Decay of the energy for the Cauchy problem of the wave equation of variable coefficients with a dissipation is considered. It is shown that whether a dissipation can be localized near infinity depends on the curvature properties of a Riemannian metric given by the variable coefficients. In particular, some criteria on curvature of the Riemannian manifold for a dissipation to be localized are given.
基金The authors are grateful to the financial support from the Key Research and Development Program sponsored by the Ministry of Science and Technology(MOST)(2022YFA1203400)the National Natural Science Foundation of China(22102172,22372155,22072145,22005294,21925205,21721003)the authors also thank the ZEROVISION company for providing assistance in creating figures for this manuscript.
文摘The discovery of single-atom catalysts(SACs)represents a groundbreaking advancement in the field of catalysis over the past decades.With the in-depth exploration of relevant structure-activity relationships,the metal−support interaction(MSI)is widely adopted to elucidate variations in electronic structure and coordination configuration of atomic active sites on various kinds of supports.Herein,we briefly summarize the metal oxide supports for SACs fabrication,including the distinctive characteristics of metal oxide supports,enlightening advancements in metal oxide support-based SACs(MO-SACs),feasible preparation methods for MO-SACs and effective regulation strategies of MSI effect in MO-SACs.In addition,we present our viewpoints and outlook in this field to stimulate rational design and construction of novel MO-SACs applied in diverse renewable energy devices,while some universal suggestions are sincerely given to provoke thoughtful considerations during the research process.
基金supported by the National Science Foundation of China under Grants Nos. 60225003, 60334040, 60221301, 60774025, and 10831007Chinese Academy of Sciences under Grant No KJCX3-SYW-S01
文摘This paper considers the existence of global smooth solutions of semilinear schrSdinger equation with a boundary feedback on 2-dimensional Riemannian manifolds when initial data are small. The authors show that the existence of global solutions depends not only on the boundary feedback, but also on a Riemannian metric, given by the coefficient of the principle part and the original metric of the manifold. In particular, the authers prove that the energy of the system decays exponentially.
文摘This paper analyses harmonic distortion caused by the narrow pulse problem in matrix converters,and presents an improved switching pattern that is based on the basic five vector switching pattern.With limited switching frequencies,the improved pattern solves the narrow pulse problem by applying an additional zero vector and adjusting the sequence of the four active vectors at the same time to minimize the switching times.Simulation results show that in the six vector switching pattern,a)the low-frequency harmonics caused by the narrow pulse problem are greatly reduced;b)the average switching frequency is reduced compared with the five vector pattern;c)the sampling frequency harmonics are apparently attenuated though a little 1/2 and 3/2 sampling frequency harmonics are produced;d)the THD of the output current is improved to the same level of the three zero vector switching pattern(TZVSP);e)the proposed switching pattern has benefits in both normal and unbalance input voltage conditions.Experimental results on a matrix converter platform,verify the benefits of the six vector switching pattern.Faster dynamic,lower harmonics and lower losses can be achieved by using the proposed six vector switching pattern.
