Studies On Preparation And Catalytic Performance Of Non-Noble Metal Oxygen Reduction Catalysts

With the rapid development of human society,fossil fuels are consumed on a large scale.It is urgent to develop some new,environmentally friendly and sustainable energy and energy conversion technologies,including metal-air batteries and proton exchange membrane fuel cells.Generally,oxygen reduction reaction（ORR）on cathode is the key reaction for these strategies.However,due to the slow kinetic process compared with anodic hydroxide,a large number of Pt-based catalysts are needed,resulting in high cost of related energy conversion equipment.Therefore,there is a need to develop non-noble metal catalysts with low cost,high activity for electrocatalytic ORR reaction.Recently,transition metal coordinated nitrogen-carbon materials（M-N_x-C）have been discovered as potential ORR electrocatalysts to substitute the Pt-based catalysts because of their attractive ORR performance in the field of electrocatalysis.In this paper,different high-performance carbon-based oxygen reduction catalysts were developed by designing their specific structure,morphology and composition.The specific research contents are as follows:（1）Porous graphene-like carbon catalysts with high density of Fe-N_x sites for oxygen reduction were prepared by high temperature treatment.During this process,Fe-g-C₃N₄ was used as template and iron source,and polydopamine was synthesized in situ as carbon source.The half-wave potential of optimal catalyst reached 0.892 V in alkaline medium,which was 50 m V higher than that of commercial Pt/C catalyst.At the potential range from 0.3 V to 0.8 V,the measured electron transfer number was between 3.96 and 3.99,indicating that the catalyst of C-Fe-g-C₃N₄@PDA held a4-electron pathway during ORR process.After 25000 s for i-t test,the current density of C-Fe-g-C₃N₄@PDA remained 89%,suggesting better stability than that of Pt/C catalyst.（2）We employed a facile adsorption-calcination approach to prepare exclusive Cu-N_x moieties embedded in porous carbon polyhedrons.Zeolite imidazole ester framework（ZIF-8）material with high surface area was used to adsorb metal precursor salt to synthesize catalyst by high-temperature pyrolysis.Further,their physicochemical characterizations were studied by various methods.For the catalytic activity in 0.1 M KOH solution,the CuNC-1100 exhibited the best ORR performance（0.885 V）.During i-t tests,the current density of CuNC-1100 catalyst remained 93%after running 25000 s,which was obviously better than that of commercial Pt/C.Additionally,the catalyst almost followed the 4-electron mechanism reaction pathway in ORR process.