高指数晶面纳米催化剂的电化学制备及应用

Electrochemical Preparations and Applications of Nano-Catalysts with High-Index Facets

催化剂的性能与其表面结构及组成密切相关,高指数晶面纳米晶的表面含有高密度的台阶原子等活性位点而表现出较高的催化活性.本文综述了电化学方波电位方法用于Pt、Pd、Rh等贵金属高指数晶面结构纳米晶催化剂的制备、形成机理及其电催化性能的研究.针对贵金属利用率问题,还着重介绍了具有较高质量活性的小粒径Pt二十四面体的制备.在此基础上,还介绍了电化学方波电位方法用于低共熔溶剂中制备高指数晶面纳米晶,以及高指数晶面纳米催化剂的表面修饰及应用;最后对高指数晶面纳米催化剂的发展做出了展望.

The performance of catalysts highly depends on their surface structure and composition. Nanocrystals bounded by high-index facets usually exhibit high catalytic activity due to their high-density low-coordinated step atoms with high reactivity. In this paper, we have reviewed the preparations of noble metals(e.g., Pt, Pd and Rh) nanocatalysts with high-index facets by electrochemi cal square-wave potential method developed in our group. The square-wave potential method includes a nucleation procedure to generate nuclei, followed by a square-wave potential procedure for a certain period of time for the growth of nuclei into nanocrystals. The formation mechanism of high-index facets is also discussed. The surface structure was determined by the combined effect of nanocrystals growing at the lower potential and etching at the higher potential, as well as the rearrangement effect by the repetitive adsorption/desorption of oxygen species induced by the square-wave potential. By tuning the upper or lower square-wave potential, the evolution of Pt nanocrystals can be controlled from tetrahexahedron to hexoctahedron, and then to trapezohedron, or from tetrahexahedron to truncated ditetragonal prism. Considering the importance in utilization of noble metal in practical applications, emphasis is also given to the small-sized Pt tetrahexahedron of high mass-specific activity. By combining seed-mediated method with square-wave potential method, sub-10 nm tetrahexahedral Pt nanocrystals enclosed with {210}high-index facets were synthesized from 3 nm Pt nanoparticles. We have then described the application of electrochemical square-wave potential method for the synthesis of high-index faceted nanocrystals in deep eutectic solvents. Pt concave nanocubes with {hk0} facets, Pt triambic icosahedra with {hhl} facets, Pd concave-disdyakis triacontahedra with {hkl} facets, and concave Au hexoctahedra with {hkl} facets and trisoctahedra with {hhl} facets were synthesized. To further boost the catalytic activity, surface modification of foreign atoms on high-index faceted metal nanocrystals including the modification of Cu on Pd tetrahexahedra to tune the selectivity of electro-reduction of CO2 is presented. Finally, an outlook of high-index faceted nanocatalysts is given.