Controllable Preparation And Electrocatalytic Performance Of Co-Based Electrocatalysts Derived From MOF Compounds For Oxygen Reduction Reaction In Alkaline Medium

Fuel cells have attracted increasing attention because of friendly environment, long theoretical service life and high efficiency. Yet, the sluggish kinetics of oxygen reduction reaction (ORR) severly limits the application range of fuel cells. Up to date, Pt-based catalysts are still the best ORR catalysts whereas the high cost and scarcity of Pt metal on the earth hinders thee commercialization of fuel cells. Therefore, it remians a big challenge to develop high performancce electrocatalysts towards ORR.Metal-organic frameworks (MOFs) is one kind of porous materials and self-assembly by covalent bond or ionic-covalent bond between transition metal atoms cluster and multiple tooth carboxylate ligands. MOFs is one kind of potential structure template materials with excellent pore structure and high specific surface area.In this work, Co-containing MOF precursors with different N incorporation were prepared in a solvothermal route and then the obtained MOF precursors were calcinated to produce Co/N-CNT and Co-N-C catalysts under nitrogen atmosphere. Furthermore, various characterization techniques were used to analyze crystal structure, morphology, pore and electrocatalytic performance.(1) A series of Co/N-CNT catalysts with different N-containing content were prepared by calcination of the Co-MOF precusors at different temperature, which were obtained by using melamine as nitrogen source in a solvothermal route. Among the prepared samples, Co/N-CNT-800 (pyrolyzed at 800℃) had the uniform size with the length of 500 nm and the width of 40 nm, the highest nitrogen content of 3.43%, and the highest specific surface area of 138.87 m2g-1. Furthermore, Co/N-CNT-800 sample has the highest ORR electrocatalytic performance with the onset potential of 0.89 V vs. RHE, the half-wave potential of 0.81 V vs. RHE, the limited current density of-3.84 mA·cm-2, and higher stability compared to Pt/C in 0.1 M KOH at the rotating speed of 1600 rpm.(2) Assisted with surfactant SDS (sodium dodecyl sulfate), a series of Co-N-C catalysts with different N-containing content were prepared by calcination of the Co-MOF precusors at 800℃ under nitrogen, which were obtained by using hexamethylenetetramine as nitrogen source in a solvothermal route. Surfactant can effectively prevent from loss of N during the calcination and then favors to enhance the electrocatalytic performance. When the usage amout of the SDS was two times than that of Co-MOF, Co-N-C-3 catalyst has the highest nitrogen content of 4.77%, the highest specfic surface area of 128.14 m2·g-1, and the best ORR catalystic performance with the onset potential of 0.84 V vs. RHE, the half-wave potential of 0.75 V vs. RHE, the limited current density of -4.37 mA·cm-2 but less stability to Pt/C after 18 000 s of continuous operation in 0.1 M KOH at the rotating speed of 1600 rpm.