Multi-Dimensional Cu-Co-Mo Metal Complex Electrocatalyst For Electrocatalytic Water Splitting

Owing to the limited natural fossil energy sources and current global environment crisis,there has been a growing need for clean energy resources as alternatives to fossil fuels,which are widely recognized as the only feasible option to ensure a sustainable development of the world economy and society.As a secondary energy source,hydrogen is regarded as the most ideal clean energy source because of its advantages of clean,pollution-free,efficient and storable.Electrochemical water splitting to produce hydrogen to generate clean fuels from renewable energy sources have been widely attracted through cathodic hydrogen evolution reaction（HER）and anodic oxygen evolution reaction（OER）.However,the electrocatalytic efficiency is usually very low in the HER and OER process due to the inevitable large dynamic overpotential and slow kinetics,which significantly confined the development of overall water splitting.Therefore,electrocatalyst is needed to reduce the energy of water splitting,and to save hydrogen production costs.As benchmark electrocatalysts,noble metal（Pt）and noble metal oxide（RuO₂and IrO₂）are suffciently active in HER and OER,respectively,while suffering from high cost and scarcity.In this paper,the following study was conducted on the optimization of HER and OER performance of non-noble electrocatalyst in 1M KOH.Firstly,Mo doped Cu/Cohybrid oxides were prepared successfully by a two-step approach:hydrothermal chemistry reaction and dehydration/reduction.The technology of dehydration/reduction at relative low temperature and the doping of Mo led to a complicated structure consisting of polycrystalline,hybrid crystal structure and amorphous structure,and complicated constituents including at least Cu,Cu₂O,CuO,CoO,CuCoO₂and Cu₂CoO₃.The subsequent highly developed interface,enhanced conductivity,larger active surface area,abundant oxygen vacancy,and redistribution of electron among these elements underwent the reason of significantly enhanced electrocatalytic activity in comparison with the cases with different Mo contents.Upon optimization,the Mo-doped Cu_2.5CoO_x（1.2%）exhibited excellent catalytic activity with an overpotential of 88 m V to obtain a current density of 10 m A cm^-2in alkaline electrolyte with scarcely any loss of the initial catalyst activity for 28 h and over 5000cycles.Secondly,Cu（OH）₂nanorod arrays were firstly created by using a 3D porous Cufoam as the precursor at room temperature.The second step was to assemble CoMoO₄·0.9H₂O nanosheets on the surface of Cu（OH）₂nanorod arrays via the hydrothermal precipitation.The hierarchical core-shell structure of Cu（OH）₂@CoMoO₄·0.9H₂O/CF increased the ECSA and electrical conductivity of materials.Remarkably,the Cu（OH）₂@CoMoO₄·0.9H₂O/CF with hierarchical structure has even better catalytic activity.The Cu（OH）₂@CoMoO₄·0.9H₂O/CF yields a current density of 10 m A cm^-2at an overpotential of merely 109 m V of HER performance.Under a current density of 10 m A cm^-2,the Cu（OH）₂@CoMoO₄·0.9H₂O/CF could maintain～80%of its initial catalytic activity.Impressively,the Cu（OH）₂@CoMoO₄·0.9H₂O/CF requires the overpotentials of 290,395,and 498 m V to reach the benchmark current densities of 10,20,and 100 m A cm^-2towards the OER test.Moreover,with regard to the long-term stability of electrocatalysts,the OER activity of Cu（OH）₂@CoMoO₄·0.9H₂O/CF in alkaline medium presents no obvious degradation even after 23 h.In summary,the non-noble catalyst of Mo-doped Cu_2.5CoO_x（1.2%）and Cu（OH）₂@CoMoO₄·0.9H₂O/CF can increased the water splitting reaction activity and enhance electrochemical durability.This work may encourage the development of new cost-effective and performance-enhanced catalysts for HER and OER.