嵌入式铂基多面体－多孔氮掺杂碳复合催化剂的可控制备与电催化性能研究

It’s of great importance for large-scale application of Fuel Cells to develop catalysts with high performance for the oxygen reduction reaction (ORR) at reasonable cost. Common issues with catalysts include poor stability and low activity for the ORR. To address some of these issues, we propose a novel composite catalyst, a Pt-based core-shell polyhedron catalyst encapsulated in nitrogen-doped carbon layer. First, PtM (M=Fe, Ni, etc.) alloy polyhedrons will be first synthesized by a wet-chemistry method, and then coated with SiO2 to form PtM@SiO2 core-shell, followed by deposition of PtM@SiO2 on carbon black. A polymer is used to coat the surface of PtM@SiO2/C via an in-situ polymerization method for forming PtM@SiO2@PN/C. The Pt1-xM@Ptx@NCL/C composite is finally yielded by heat treatment and removing SiO2. Pt1-xM@Ptx polyhedrons converted from the PtM alloys not only have the advantages of Pt-rich core-shell structure, but also maintain the highly active surface. Moreover, the stability of the Pt1-xM@Ptx@NCL/C catalyst can be boosted by porous nitrogen-doped carbon layer (NCL) originated from pyrrolyzation of polymer which can improve corrosion resistance of the carbon support, and effectively suppress the migration and aggregation of the Pt1-xM@Ptx polyhedrons on the carbon support. Furthermore, the performance of Pt1-xM@Ptx@NCL/C can be further enhanced by the synergistic effect between NCL and Pt1-xM@Ptx polyhedron. This strategy could be easily used to develop a wider range of other electrocatalysts with better activity and extraordinary stability.

发展低成本、高性能的氧还原催化剂是推进燃料电池规模化应用的关键。针对现有催化剂存在的稳定性差和活性低的问题，本项目拟发展嵌入式铂基多面体－多孔氮掺杂碳复合催化剂。在PtM合金多面体表面包覆SiO2，并分散在碳黑表面形成PtM@SiO2/C；再包覆含氮聚合物（PN）形成PtM@SiO2@PN/C；在高温和SiO2隔离限制下，PtM和PN分别转变为Pt1-xM@Ptx核壳多面体和多孔氮掺杂碳层（NCL）；最后除去SiO2得到Pt1-xM@Ptx@NCL/C复合催化剂。该催化剂中Pt1-xM@Ptx多面体不仅有核壳结构优势，且能保留高活性晶面，从而提高催化性能；多孔NCL不仅有良好的耐腐蚀性能，且能抑制Pt1-xM@Ptx多面体的迁移团聚，从而提高催化剂整体的稳定性；同时，Pt1-xM@Ptx多面体与多孔NCL的协同作用有利于增强催化剂的性能。本项目的设计方案有望拓展到其他高性能催化剂的制备。

发展低成本、高性能的低铂催化剂是实现燃料电池规模化应用的关键之一。针对现有催化剂存在的稳定性差和活性低的问题，本项目提出了嵌入式铂基多面体－多孔氮掺杂碳复合催化剂方案。在项目执行过程中发表论文4篇，其中SCI论文4篇，培养研究生3名。取得的创新性成果有：（1）开发了基于“高温诱导”和“空间限域”的催化剂结构演变方法，实现了从无序Pt基合金纳米粒子到三元有序L10-PtFeCo合金纳米粒子的结构转化，同时精确调控Pt电子结构。合成的L10-PtFeCo合金催化剂在0.9V(vs.RHE)下的质量活性达到1.43A/mgPt，是商业化Pt/C催化剂的8.41倍，为美国能源部2020年目标0.44A/mgPt的3.25倍。此外该催化剂经过20000圈CV加速老化测试后合金颗粒形貌和分布没有发生明显变化，半波电位（E1/2）仅损失8mV，远优于商业化Pt/C催化剂的表现（E1/2损失32mV）。（2）首次通过原位还原的方法利用单原子分散的Fe/Zn-N-C材料为载体制备了一种稳定高效的单层PtRu复合催化剂。（3）探究了无保护层制备粒径小于4纳米有序L10-PtCo合金催化剂。