Controlled Synthesis And Catalytic Properties Of Copper Based Electrocatalysts For Water Splitting

At present,energy and environmental issues have become the key to the sustainable development of economy,and hydrogen production from electrochemical water splitting is considered to be one of the most effective ways to solve the above problems.The water splitting reaction includes two half reactions,oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）.In the half-reaction process,especially the OER process,the multiple electron transfer step will generate a large overpotential,which will result in huge energy consumption,thus limiting the industrial application of water splitting reaction.Electrocatalyst,however,can greatly reduce the overpotential of electrochemical water splitting.In theory,noble metal-based catalysts are considered to be the best elect rocatalyst due to its most suitable free energy value of hydrogen（oxygen）adsorption,but their large-scale applications have been limited by their high price and rare reserves.Therefore,exploring non-noble metal-based catalysts with high activity and s tability has become the only way to realize the industrialization of electrochemical water splitting.Based on the characteristics of Cu based materials,such as multiple types,easy to obtain and low price,combined with the limited electrocatalytic activ e sites and poor stability of Co/Fe based materials,this paper takes Cu/Co/Fe based composite materials as the research object to realizes the nanoscale composite of materials through reasonable structure design and simple chemical methods.In this paper,the composite mechanism was proposed by adjusting the experimental parameters and analyzing the characterization data,and at the same time,through the optimization of material structure,defect design,element doping,and visible light activation,which help to achieve effective control of the catalyst active sites and conductivity,a high catalytic activity electrocatalysts was obtained.The specific work is as follows:1.Bifunctional Cu₂S-Co（OH）₂nanotube array/Cu foam electrocatalyst for overall water splitting.Cu（OH）₂ NRA/CF was synthesized on the copper foam（CF）by in-situ oxidation,and then used as precursor to obtain Cu ₂S-Co（OH）₂NTA/CF by a simple four step chemical reaction process（sulfidation,etching,reduction and cobalt-growth）,during which the effective control of the nanotube cavity diameter can be realized by adjusting the Na₂S concentration.The results show that the nanotube array structure greatly increases the specific surface area of the composite catalyst,which is conducive to the exposure of more catalytic active centers and greatly improves the electrocatalytic kinetics.Cu₂S-Co（OH）₂NTA/CF shows excellent HER,OER and overall water splitting electrocatalytic performance in alkaline environment.At a current density of 50 mA cm^–2,the overall water splitting overpotential is 560 mV,and the stability of continuous overall water splitting can reach 100 h..2.The construction of CoS-Co（OH）₂nanoflakes@Cu₃₁S₁₆ microrod architectures for alkaline overall water splitting.Using a one-step Na₂S₂O₃-activation strategy,by adjusting the activation time（10～240 min）,a series of Co-Cu_xS composite catalysts were obtained.The results show that the Co-Cu_xS-240 electrocatalyst is a one-dimensional rod-like yolk shell structure with Cu₃₁S₁₆ nanorod as the core,Co（OH）₂ultrathin nano sheet loaded with CoS quantum dots as the shell,and a small amount of Cu₂O as the bridge connecting the OER active Center（Co（OH）₂and CoS）and HER active center(CoS and Cu₃₁S₁₆).The synergistic effect between the various components makes Co-Cu_xS-240 exhibit excellent alkaline OER,HER and overall water splitting catalytic activity and stability.At a current density of 50 mA cm^–2,the overpotentials of OER,HER and overall water splitting are only 268,143 and 450 mV.3.Synthesis of Fe（OH）₃ NP-Cu₂O/SNS and photoactivation to promote alkali water oxidation.A one-dimensional nanorod array（Fe（OH）₃ NP-Cu₂O/SNS）composed of Cu₂O nanosheets with amorphous Fe（OH）₃ nanoparticles on the surface was obtained by one-step synthesis assisted by H₂O₂.The relatively open structure of Cu₂O nanosheets accelerates the diffusion rate of electrolyte and electrons,and at the same time,it can expose more catalytic active centers of Fe（OH）₃ nanoparticles.The results show that Fe（OH）₃ NP-Cu₂O/SNS exhibits excellent OER electrocatalytic performance in alkaline media.At a current density of 50 mA cm^–2,its over potential is only 260 mV.At the same time,the stable structure of the Fe（OH）₃ NP-Cu₂O/SNS composite catalyst makes it exhibit excellent stability and rate performance in the i-t test of up to 50 hours and the C-P test of up to 60 hours at different current densities(10,50,100,150 and 200 mA cm^–2).Additionally,photoactivation strategy using simulated the visible light of the sun to irradiate Fe（OH）₃ NP-Cu₂O/SNS samples can further improve the OER electrocatalytic activity of it.4.Controlled synthesis and catalytic properties of defect-rich and Co-doped Cu₂Cl（OH）₃ electrocatalysts for water splitting.A one-pot method,using thiourea as the main reactant,and by reasonably controlling its concentration,was used to synthesize the Co-doped Cu₂Cl（OH）₃ catalyst with rich defects（denoted as D-Co-Cu₂Cl（OH）₃）.HRTEM results show that the defects,which mainly exist on the surface of hexagonal sheet Cu₂Cl（OH）₃,greatly improve the electrocatalytic inert body of Cu₂Cl（OH）₃ and effectively increase the electrocatalytic active sites;meanwhile,Co doping changes the electronic structure of the material and greatly improves the conductivity of the material.The synergistic effect of the two species significantly improves the electrocatalytic activity of the material.The electrochemical test results show that the D-Co-Cu₂Cl（OH）₃ catalyst exhibits excellent alkaline OER,HER and overall water splitting catalytic activity,and is a very excellent bifunctional electrocatalyst for overall water splitting,the overpotentials of OER,HER,and overall water splitting are only 261,232 and 500 mV at a current density of 50 mA cm^–2.Meanwhile,i-t curve lasting up to 60 hours reveals its outstanding overall water splitting stability.5.Yolk-shell Co（OH）₂@CuCl electrocatalysts for the alkaline electrocatalytic water oxidation.A yolk-shell Co（OH）₂@CuCl nanocubic composite catalyst was synthesized by a simple chemical method using CuCl as a precursor.The electrochemical results show that the yolk-shell Co（OH）₂@CuCl nanocubes exhibit the best OER catalytic activity.At a current density of 50 mA cm^–2,the overpotential is only 372 mV.More importantly,CuCl is applied to the field of electrocatalysis for the first time,which will provide a good reference for the research of CuCl in the field of electrocatalysis.