The Fabrication Of Cobalt-based Compound Nanomaterial And The Study Of Its Electrocatalytic Properties

Electrocatalysts have been widely used in renewable energy devices such as metal-air battery and water splitting.Much efforts have been devoted to catalysts for Oxygen Reduction Reation?ORR?Oxygen Evolution Reation?OER?and Hydrogen Evolution Reaction?HER?for decades.In recent years,bifuntiansl catalysts for ORR/OER and OER/HER gradually become the hot spot for researchers.Noble metal based catalysts like Pt RuO₂ and IrO₂ are identified as the best electrocatalysts for ORR HER and OER.However,owing to its scarcity high-cost and instability,the large scale applications of renewable energy devices are limited.Therefore,preparation of efficient and stable non-precious metal based catalysts is the core of the issue.At present,the active site of the non-noble metal based nanomaterials is ambiguous.As a result,it's necessary to study where the active site truly locates.In this article,a facile hydrothermal approach has been developed for controlled synthesis of Co₃O₄ nanocrystals on N-doped graphene without using template and additive.By tuning the usage of the NH₃?H₂O,we controllably synthesize the crystallized Co₃O₄ nanocube?NC?,nanotruncated octahedron?NTO?,nanopolyhedron?NP?with different exposed crystal planes in-situ anchored on nitrogen-doped reduced graphene oxide?N-rGO?.The as-prepared three Co₃O₄nanocrystals are enclosed by{100},{100}+{111},and{112}planes,respectively,which are featured by different concentrations of Co²⁺and Co³⁺metal sites.Our results revealed that the Co₃O₄-NP/N-rGO surrounded by unusual{112}crystal planes exhibits the superior ORR/OER and Zn-air battery performance than those of Co₃O₄-NC/N-rGO and Co₃O₄-NTO/N-rGO counterparts including lower overpotentials and faster catalytic kinetics.The richer exposed highly active catalytic sites of Co³⁺in octahedral interstices(Co³⁺oct)on{112}facet and the coupling interaction between Co₃O₄ and N-doped graphene in Co₃O₄-NP/N-rGO synergistically favor the adsorption/desorption and activation of oxygen species,thus benefit the electrocatalytic ORR and OER kinetics during the discharge and charge processes of metal-air batteries.Additionally,we synthesize of pyrite-type bimetallic Ni-doped CoS₂nanoneedle arrays supported on stainless steel(Ni_xCo_1-xS₂ NN/SS,0?x?1)and the related compositional influence on electrocatalytic efficiencies for oxygen and hydrogen evolution reaction?OER/HER?.Impressively,the Ni_0.33Co_0.67S₂ NN/SS displays superior activity and faster kinetic for catalyzing OER and HER than those of counterparts with other Ni/Co ratios and also monometallic Ni-or Co-based sulfides,which is attributed to the optimized balance from the improved electron transfer capability,increased exposure of electrocatalytic active sites,and favorable dissipation of gaseous products over nanoneedle surface.