{111}晶面暴露的中空Pt-Ni纳米壳的构筑及其氧还原电催化性能研究

The enhancement of Pt mass activity towards oxygen reduction and the inhibition of the degradation of activity under dynamic working conditions have always been the research hotspot in the field of electrocatalysis. The mass activity is co-determined by the area-specific activity and electrochemical active surface are (ECSA) of Pt. In order to enhance the Pt mass activity and its durability towards oxygen reduction at the same time, the crystalline plane regulation, alloying and hollowing strategy are combined to construct {111}-plane-exposed hollow Pt-Ni nanoshells which are prepared by templating method followed by thermal annealing to induce Pt-skin on the surface. In this novel catalyst, the Pt-Ni{111} crystalline plane with Pt-skin has superior area-specific activity, while the hollow structure will give rise to high ECSA. As for the durability, the Pt-skin can protect the Ni element in the alloy from dissolving; the highest coordination number of Pt{111} plane and the lattice contraction induced by the cavity is beneficial to suppress the oxidation and the subsequent dissolving of Pt atoms, hence the durability of area-specific activity and ECSA can be improved simultaneously. In this project, the formation mechanism of the novel structure and the regulation mechanism to the microstructure will be studied through detailed analysis of plane, alloy and hollow structure, respectively. On the basis of controllable preparation, the electrochemical properties evaluation and theoretical simulation are employed to investigate the relationship between microstructure and performances for the {111}-plane-exposed Pt-Ni nanoshells. The expected results will perfect the electrocatalytic theory of oxygen reduction and provide experimental support and theoretical guidance on the design of high-performance electrocatalysts for oxygen reduction.

提高Pt的氧还原质量活性并避免其在动电位环境下的衰减是电催化领域的研究热点与重点。质量活性由面积活性与电化学比表面积共同决定。本项目拟将Pt基催化剂的晶面调控、合金化以及空心化策略联合运用，采用模板法构筑{111}晶面暴露的中空Pt-Ni纳米壳，并通过热处理诱导表面形成Pt偏析层，以同时提高催化剂的质量活性和电化学稳定性。该结构的优势在于：1）Pt表面偏析的Pt-Ni{111}晶面和中空结构分别具有优异的面积活性和电化学比表面积；2）Pt偏析层可抑制Ni元素的流失，{111}晶面的高配位数及空心化带来的晶格收缩有助于减缓Pt原子的氧化溶解。本项目将从材料的制备入手，通过对催化剂晶面结构、合金结构及空心结构的详尽解析，揭示纳米壳的形成机制及其微观结构的调控机制。在此基础上，通过电化学性能评价和理论计算，建立催化剂微观结构与其宏观性能的内在联系，为设计高性能氧还原催化剂提供实验依据与理论指导。

暴露高活性的{111}晶面和制备空心结构是提高Pt基材料氧还原催化活性的重要方法。本项目首先以聚氧乙烯-聚氧丙烯-聚氧乙烯嵌段共聚物为还原剂成功合成了{111}晶面暴露的Pd纳米粒子。在此基础上，合成了具有丰富{111}晶面暴露的Pd@Pt核壳结构催化剂，在0.1 M HClO4中测试其质量活性达到0.33 A/mgPt，并且在连续动电位扫描过程中发现其转变为空心PdPt合金结构，在这一过程中氧还原活性得以维持。进一步地，我们合成了八面体Pt-Ni纳米框架，其质量活性达到0.48 A/mgPt，并且在经过0.6-1.0 V三万圈的循环扫描后活性几乎不变，展现了优良的稳定性。此外，作为与本项目相关的研究方向，课题组开展了水电解催化剂方面的工作。先后合成了Co，N，S共掺杂石墨烯复合Co纳米粒子催化剂以及Fe掺杂的Ni3S2纳米片阵列，并对其催化析氢和析氧反应的催化性能开展了详细研究。尤其对于以Fe掺杂的Ni3S2纳米片阵列组装的电解池，在1 M KOH中达到10 mA/cm2电流密度仅需1.54 V，展现了优异的催化活性。