Molecular-Level Design and Synthesis of M-N-C Non-Precious Metal Catalysts Derived from Transition Metal-Coordinated Bis(imino)-Pyridine Based Polymers for Highly Efficient Oxygen Reduction

Abstract

Molecular-Level Design and Synthesis of M-N-C Non-Precious Metal Catalysts Derived from Transition Metal-Coordinated Bis(imino)-Pyridine Based Polymers for Highly Efficient Oxygen ReductionZhi Qun Tian*, Xiaoran Zhang, Dandan Lyu, and Pei Kang Shen Collaborative Innovation Center of Sustainable Energy Materials, Guangxi Key Laboratory of Electrochemical Energy Materials, State Key Laboratory of Processing for Non-ferrous Metal and Featured Materials, Guangxi University, Nanning，53004, China. （E-mail:tianzhiqun@gxu.edu.cn）: Transition-nitrogen-carbon (M-N-C) materials as the most promising non-precious metal catalysts for oxygen reduction reaction (ORR) to replace Pt-based catalysts are in high demand for large scale application of fuel cells. However, their activity and durability are still critical issues. Development of M/N/C-containing precursors is a straightforward strategy for obtaining advanced M-N-C ORR catalysts to address these issues. Herein, we report a new strategy for synthesizing a highly efficient and robust M-N-C catalyst for oxygen reduction reaction (ORR) via the pyrolysis of bis(imino)-pyridine metal-ligand based polymers. A series of Fe-N-C, Co-N-C and Mn-N-C catalysts prepared by the new presucors displays an excellent electrochemical performance for ORR with onset and half-wave potentials of >0.95 V, 0.84 V vs. RHE, respectively, in acidic media, and >1.0 V, 0.9 V vs. RHE, respectively, in alkaline media. These values are comparable to commercial Pt/C catalyst in acidic media and even more superior to commercial Pt/C in alkaline media. And a low H2O2 yield (< 2%) in the diffusion-limiting current region and a high electron transfer number (3.97-3.99) were achieved in our catalysts, indicating the occurance of direct 4 e- process for ORR. Meanwhile, the catalyst shows remarkable cycle stability at high potential range of 0.6-1.35V both in alkaline and acidic media, outperforming Fe-N-C catalysts reported previously, which is important for practical application of ORR catalysts in fuel cells. This feature makes it among most efficient non-precious catalysts in alkaline/acidic media for ORR. We believe this novel approach may open a new way of synthesizing highly efficient and robust noble metal-free catalysts for ORR.