The Components Regulation And Morphology Control Of Hybrid Structured Catalysts For Water Splitting By Cathodic Plasma Electrolytic Deposition

The broad development prospect of hydrogen is viewed based on its high energy density,pollution-free and sustainability.Hydrogen with high purity is produced primarily by electrochemical water splitting in industry.However,the energy loss because of high overpotential in hydrogen evolution reaction and oxygen evolution reaction increases the cost of production,and consequently to impede its application on a large scale.The utilization of electrocatalyst will lower the overpotential significantly.Traditionally,the commercial catalysts are synthesized by noble metal,which is facing both the high cost and limitations of scarcity.In the enthusiasm that comes with low cost,high activity and stability,a wide variety of transition metal-based materials has developed vigorously in recent years.The construction of heterostructure is an appealing solution for boosting the activity of electrocatalyst.However,the dominating synthetic processes for heterostructure are composed of multiple steps and time consuming.Our research team found that a rapid one-step process,cathodic plasma electrolytic deposition（CPED）,could fabricate Co Mo/Co Mo O_x with metal/oxide heterostructure and shown its tremendous potential at synthesizing heterostructured materials.Herein,further research on components regulation and morphology control is presented to improve the performance of electrocatalysis and promote the practical application of CPED.This research project was based on the previously prepared Co Mo/Co Mo O_xheterostructure.The proportion between metal and oxide in the heterostructure was optimized by adjusting the pH of electrolyte solution and adding oxidant.The overpotential for HER of Co Mo/Co Mo O_x fell to 61 m V from 88 m V at a current density of 10 m A cm^-2 due to efficient water dissociation on oxide surfaces and the benefit of arborization structure in providing more accessible active sites and faster mass transport.Unfortunately,the oxide was reduced and arborization structure shed from the substrate after a long period of hydrogen evolution,which show poor stability in HER.The morphology and composition of heterostructure were regulated by the addition of organic solvent to enhance the stability.The addition of organic solvent with low dielectric constant modified the electric field distribution near the substrate surface,resulting in uniform bubble evolution and arc distribution,as well as metal decreasing the ion concentration polarization.As a consequence,the metal ions fabricated the heterostructure composed of alloy,carbide and oxide with uniform morphology and high binding force at a lower rate.Thanks to the high conductivity,low hydrogen adsorption free energy and water dissociation energy barrier of the newly formed carbide,the Co MO-30G sample realized a significantly enhanced activity and high stability.The overpotential for HER was as low as 62 m V,and increased by 9m V after 18 hours stability test.Most importantly,this fabrication method technology could be extended to other metals as robust multifunctional electrocatalyst.Ternary Ni Fe Mo heterostructure electrocatalyst for overall water splitting was prepared by introducing iron source.The incorporation of Fe³⁺modified the electronic structure of the adjacent Ni and Mo metal sites,improving the absorption ability to hydroxyl ion and oxygenated intermediates.In addition,metal and alloy which showed the larger capacity for adsorbing hydrogen could promote the deprotonation of oxygenated intermediates.The synergistic effect improved the catalytic activity for HER and OER remarkably.As a result,ternary Ni Fe Mo heterostructure electrocatalyst showed a superior electrocatalytic performance with a current density of 100?m A?cm^-2?at 1.57 V on 3D nickel foam,the change in overpotential could be ignored after continuous electrocatalytic water splitting for 18?h.