Cube-shaped metal-nitrogen–carbon derived from metal-ammonia complex-impregnated metal-organic framework for highly efficient oxygen reduction reaction

Abstract

The non-platinum metal-nitrogen-carbon (M-NC) system is a class of highly active oxygen reduction reaction (ORR) electrocatalysts that are well known and widely used in fuel cell applications. Herein, one simple synthesizing method of efficient M-NC electrocatalysts is proposed by the direct pyrolysis of a pretreated core-shell structure of ZnO@ZIF-8 containing metal-ammonia complex (MAC, [M(NH3)x]n+) from the polydisperse self-sacrificing MOF-5 cubes. The as-pyrolyzed M-NC (M = Co, Ag, Cu, and Ni) electrocatalysts showcase high electrocatalytic ORR activity in an alkaline medium. Among them, Co-NC catalyst exhibits an excellent ORR performance where its E1/2 = 0.80 V, JL = 5.88 mA cm−2, as well as Tafel slope of 67.0 mV dec−1 are close to commercial Pt/C and Ag-NC, better than the other two catalysts of Cu-NC and Ni-NC. Impressively, zinc-O2 batteries assembled with M-NC materials exhibit the better discharge performance, and have great potential in the practical energy conversion and storage. The experimental demonstration of metal-based nanoparticles and active M-N sites in the carbonaceous matrix can be efficiently used to promote the ORR activity, which is derived from a synergistic contribution of its particular hollow structure, large specific surface area, rich M-N active sites, and high degree of graphitization. This attractive preparation approach provides us a powerful contribution to the construction of high-performance carbon-based ORR electrocatalysts.