MOF-Based Co and Mn Embedded in Nitrogen-Doped Microporous Carbon as an Efficient Catalyst for Oxygen Reduction Reaction in Anion Exchange Membrane Fuel Cell

Abstract

Developing a low-price, high catalytic activity, and strong durability electrocatalyst for alkaline oxygen reduction reaction (ORR) is significantly important for anion exchange membrane fuel cell (AEMFC). Herein, Co and Mn salts were added into ZIF-8 to obtain CoMn-ZIF-Ac-2. Co and Mn embedded in nitrogen-doped microporous carbon (CoMn-N-C-Ac-2-Ts, $T=700$ , 800, 900, and 1000°C) were obtained by carbonizing CoMn-ZIF-Ac-2 at various temperature. The influence of various pyrolysis temperature and molar ratios between Co and Mn toward ORR catalytic activity was researched. For CoMn-N-C-Ac-2-Ts, CoMn-N-C-Ac-2-800 had the highest ORR catalytic activity with the half-wave potential of 0.875 V in 0.1 M KOH, only 5 mV lower than that of 20 wt % Pt/C. Besides, high 4e- selectivity, excellent stability (retaining 100% for 20 h at 0.6 V vs. RHE), and methanol tolerance are also exhibited. In addition, CoMn-N-C-Ac-2-800 exhibited better ORR activity than Mn-N-C-Ac-800 and Co-N-C-Ac-800, which was attributed to more Co-N4, more MnIII species, and higher surface area. Moreover, the AEMFC based on the CoMn-N-C-Ac-2-800 cathode catalyst obtained a maximal power density of 291 mW·cm-2, which was 78% of the $P_{\max }$ achieved with 20 wt % Pt/C (375 mW·cm-2). The highest ORR performance for CoMn-N-C-Ac-2-800 was contributed by the highest defect degree, the most amounts of Co/Mn-N4 active site, the maximum BET surface area, and micropore structure.