Atomically dispersed Mn–N4 electrocatalyst with high oxygen reduction reaction catalytic activity from metal–organic framework ZIF-8 by minimal-water-assisted mechanochemical synthesis

Abstract

Developing efficient and stable non-precious metal oxygen reduction reaction (ORR) catalysts in an environmentally benign and economically affordable way is highly desirable but remains challenging. Manganese and nitrogen co-doped porous carbon, Mn–N–C, has recently been studied as a promising electrocatalyst for the ORR, with high catalytic efficiency and long-term stability. In this paper, we report the preparation of a highly active Mn–N–C catalyst using the metal–organic framework ZIF-8 synthesized by a minimal-water-assisted grinding method as the precursor. Due to the mechanical force exerted by the grinding, the manganese salt is finely dispersed on the ZIF-8 framework and formation of manganese oxides upon pyrolysis is efficiently alleviated, and the single-atomic Mn–N–C catalyst was obtained using the mechanochemically synthesized manganese salt-incorporated ZIF-8 as the precursor. Moreover, the minimal-water-assisted mechanochemical method enables the synthesis of manganese-doped ZIF-8 with a high yield compared with the theoretical value and much higher than the yield obtained for the widely used organic solvent synthesis method. The resultant Mn–N–C catalyst delivers a half-wave potential of 0.80 V in 0.1 M HClO₄ solution and 0.94 V in 0.1 M KOH solution; excellent stability was also achieved. The Mn–N–C was used as the cathode to assemble a zinc–air battery and a peak power density of 185 mW cm⁻² was achieved, demonstrating its promise as a practical and useable ORR catalyst.