Mesoporous, nitrogen-doped, graphitized carbon nanosheets embedded with cobalt nanoparticles for efficient oxygen electroreduction

Nitrogen-doped graphitized carbon nanosheets embedded with crystalline cobalt nanoparticles are facilely synthesized with the aid of melamine-containing hydrogen-bonded organic frameworks (HOF). Experimentally, HOF microrods with an in situ polymerized dopamine (DA) overlayer are coordinated with Co²⁺ cations and used as a precursor. After pyrolyzing the Co@DA-HOF precursor, irregular sheet-like carbons comprising a large number of Co nanoparticles as well as abundant mesopores are obtained (Co@MPC-T). The thermal decomposition of melamine-containing HOF microrods during high-temperature pyrolysis helps generate the abundant porous structures in the resulting catalyst samples. Thus, synthesized Co@MPC-T catalysts display an apparent ORR activity, and the one pyrolyzed at 800 °C is determined to show the highest ORR catalytic activity among the series, with a half-wave potential of + 0.796 V, a diffusion-limiting current density of 5.492 mA cm⁻² at + 0.200 V and a kinetic current of 51.40 mA cm⁻² that is even two times higher than the 20.10 mA cm⁻² for commercial Pt/C catalyst. Moreover, benefiting from the protection of graphitized carbon overlayer, Co@MPC-800 shows a substantially higher operation stability as well as superior tolerance to fuel crossover, as compared with the commercial Pt/C catalyst. The remarkable ORR performance of Co@MPC-800 highlights the high potential of graphitized two-dimensional carbon composites with nonprecious transition metal nanoparticles in electrocatalysis.