Preparation Of Nickel-based Composite Electrocatalyst And Its Performance In Electrolysis Of Seawate

The massive use of fossil fuels has caused a series of problems such as energy shortage and environmental pollution.It is imperative to develop clean and sustainable energy.Hydrogen（H₂）is considered as one of the most ideal alternative clean energy sources for traditional fossil energy because of its high energy density and no pollution.Compared with traditional steam reforming of natural gas,electrocatalytic water cracking has attracted much attention because of its zero carbon emission.However,limited fresh water resources may become the bottleneck of large-scale implementation of electrolysis hydrogen production technology worldwide.Seawater accounts for 96.5percent of the world’s water resources and is an almost unlimited resource.Therefore,direct electrolysis of seawater provides a very promising alternative approach for green hydrogen production.However,direct electrolysis of seawater presents more challenges.Seawater electrolysis consists of oxygen evolution reaction（OER）at the anode and hydrogen evolution reaction（HER）at the cathode.There are chloride ions in seawater,and the anodic chlorine evolution reaction（CIER）will compete with OER in the electrolysis of seawater.In addition,the presence of various ions(such as Mg²⁺,Ca²⁺,Cl^-,Br^-,etc.)and bacteria/microorganisms in seawater will cause toxicity to electrode/catalyst materials,resulting in long-term unstable operation and even deactivation of catalyst,which puts forward higher requirements for the stability of catalyst.In order to improve the OER selectivity of seawater electrolysis,the thermodynamic potential difference between OER and CIER can be maximized based on thermodynamic and kinetic considerations.In other words,the theoretical potential difference required for OER and CIER is stable at about 490 m V under alkaline conditions（p H>7.5）.Therefore,the design and development of high current density,low overpotential and stability electrocatalyst has important practical significance for seawater electrolysis.In this paper,the transition metal electrocatalyst is designed and the catalyst structure modification,material composite and electronic structure control,effectively improve the catalytic activity and stability of the catalyst.The specific research work is as follows:1.NiCo（HPO₄）₂@Ni₃N/NF（NiCo HPi@Ni₃N/NF）nanosheet array catalysts were prepared by one-step electrodeposition by cyclic voltammetry using nickel nitride（Ni₃N）supported on nickel foam（NF）as substrate.The microstructure,composition and electrochemical properties of NiCo HPi@Ni₃N/NF composite catalyst were studied.The results showed that the growth of flake NiCo HPi on Ni₃N nanosheets significantly increased the specific surface area of the catalyst and the number of catalytic active sites.Moreover,the hydrogen phosphate ion on the surface of NiCo HPi@Ni₃N/NF catalyst is a highly efficient proton receptor,which promotes the adsorption of OH^-and thus promotes the OER reaction.NiCo HPi@Ni₃N/NF showed excellent electrocatalytic performance for both HER and OER in simulated seawater.In 1 M KOH+0.5 M Na Cl solution,the current density of 100 m A cm^-2 can be reached when the overpotential of OER and HER is 365 and 174 m V,respectively.Using NiCo HPi@Ni₃N/NF electrode as both cathode and anode to construct the cell,the current density of 500 m A cm^-2 can be achieved when the cell voltage is 1.99 V in alkaline seawater analog electrolyte.This work provides inspiration for the design and exploration of efficient electrocatalyst for hydrogen production by seawater electrolysis.2.Flake Ni（OH）₂@NiFe₂O₄@Ni₃S₂/NF nanostructured electrocatalyst was synthesized by one-step hydrothermal method.Ni（OH）₂@NiFe₂O₄@Ni₃S₂/NF showed excellent OER electrocatalytic activity and stability in alkaline electrolyte.The overpotential of the catalyst is 301 m V and 413 m V at 100 and 1000 m A cm^-2 current densities in alkaline natural seawater,respectively.In addition,Ni（OH）₂@NiFe₂O₄@Ni₃S₂/NF can maintain good performance for more than 100hours when reaching 500 m A cm^-2 in alkaline seawater.Compared with Ni₃S₂ catalyst,the composite catalyst Ni（OH）₂@NiFe₂O₄@Ni₃S₂/NF has a nano-sheet structure with a large specific surface area and the number of active sites.Through XPS,the Ni（OH）₂@NiFe₂O₄@Ni₃S₂/NF catalyst has phase interaction,which promoted the OER reaction.This work provides a new reference for designing stable catalysts for seawater electrolysis.