Construction Of Cobalt-Ni-based Multicomponent Composite Nanomaterials And Study On Their Photoelectrochemical Seawater Decomposition Performanc

In recent years,the increasingly serious energy and environmental crisis has led to the promotion of sustainable green energy around the world.Among all kinds of renewable energy,hydrogen has broad application prospects because of its completely green and carbon-free production and use process.As the freshwater resources on the earth are very valuable,the electrolysis of seawater to produce hydrogen has become a hot spot.Bifunctional catalysts have received widespread attention due to their advantages of simplifying the system and reducing the operating costs.In order to make the whole water decomposition go on smoothly,the catalysts for hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）must work normally in the same electrolyte.Therefore,we set out to look for bifunctional catalysts that are active for both HER and OER processes in the same electrolyte.Considering that the actual water electrolysis efficiency of HER and OER is greatly inhibited by the overpotential,the electrode surface used for water decomposition is usually coated or modified with electrocatalytic materials to reduce the overpotential and improve the hydrogen production efficiency.In addition,seawater decomposition has certain requirements for corrosion resistance of catalytic materials.Therefore,it is very important to find a catalytic material with low overpotential and good corrosion resistance.Transition metals nickel（Ni）and cobalt（Co）and their compounds,such as oxides,hydroxides,nitrides and carbides,are characterized by high activity,environmental protection and rich reserves of earth resources.The following are two kinds of catalytic materials designed based on Ni-Co alloy in this paper,which can improve the performance of catalytic water decomposition and water decomposition in seawater,as follows:（1）Using simple hydrothermal method,the specific surface area of（Co,Ni）OOH LDHs can be increased and the active sites can be more easily exposed by controlling the concentration of urea to obtain different forms of（Co,Ni）OOH LDHs.The electrocatalytic activity of（Co,Ni）OOH LDHs was improved.Electrochemical tests show that（Co,Ni）OOH LDHs nanowires have low overpotential in seawater,and have better performance and excellent stability in HER and OER.（2）Photoelectrochemical（PEC）seawater splitting,avoiding consumption of freshwater,is an intriguing strategy for sustainable hydrogen.The weak alkalinity of seawater,and the released caustic hypochlorite during seawater splitting,compel the low-cost catalytic materials that are resistant to both alkali and acid to be of great significance.Inspired by branching algae,we develop an ultra-robust photoelectrocatalysts that the WO₃ nanorods（NRs）are evenly passivated by heavily N/W co-doped（Co,Ni）O_xN_y layer and decorated by（Co,Ni,W）O_xN_y porous nanosheets（NSs）,which possess multiple crystal phases including oxide and tungstate of Co and Ni.Firstly,heavily doped N atoms originate from the ammonia-complexed（Am C）Co-Ni ions during the hydrothermal synthesis of（Co,Ni）O_xN_yH_x+y NSs.After calcination accompanied by the sublimation of W,the porous（Co,Ni）O_xN_y porous NSs are doped with W,and the resultant（Co,Ni,W）O_xN_y/WO₃ hetero-nanorods（HNRs）demonstrate PEC current density about 0.35 m A/cm² at 1.23 vs.RHE with good durability over 100 hours in natural seawater.DFT calculations reveal that the doped W atoms trigger obvious lattice distortion in NSHs with multiple crystal phases,and that the evacuation of all the 5d electrons makes W atoms as donor centers and active sites,leading to the enhanced catalytic activity and the inhibited corrosion of Co-Ni atoms.Furthermore,the N atoms expand the energy range of the conduction band and facilitate more electrons to participate in the PEC reaction.This work provides a practical strategy towards the durable PEC anode materials for seawater splitting.