Synthesis Of Noble-metal-free Nanostructured Catalysts For Electrochemical Water Splitting

Compared with conventional hydrogen production technology from steam reforming using fossil fuels,water electrolysis is widely regarded as a green and clean method for large-scale hydrogen production,which will play an important role in addressing the issue of energy crisis and achieving carbon neutrality.In the process of water electrolysis,there is large overpotential for both the hydrogen evolution reaction（HER）at cathode and the oxygen evolution reaction（OER）at anode to overcome the reaction kinetics barrier,resulting in low efficiency of hydrogen production from water splitting.Therefore,it is of great significance to investigate highly active catalysts for both HER and OER to reduce the energy barriers and accelerate the reaction kinetics.Although noble Pt-based and Ru-based electrocatalysts have been found to exhibit favorable catalytic activity,the scarcity and high cost of these materials hinder their large-scale application.Meanwhile,abundant and cheap transition metal Ni,Mo,Fe,and Co-based materials have also been reported to demonstrate excellent catalytic performance in water electrolysis,bringing these materials to research hotspot centers.Moreover,water electrolysis under commercial conditions is more demanding than that under laboratory conditions,while most of the superior catalysts prepared in the laboratory are reluctant to be applied commercially due to tedious preparation process.Therefore,it is significant to explore the simple methods to prepare non-precious metal catalysts for water splitting towards commercial applications.Therefore,in this thesis,a simple one-step electrodeposition method was developed to in-situ growth prepare Ni-Ni Mo O_x nanoparticles on nickel foam for efficient HER under alkaline conditions.Through a series of characterizations,it was revealed that the in-situ growth nanoparticle structure showed a large specific surface area to provide more active sites.At the current density of 10 m A cm^-2,the overpotential of Ni-Ni Mo O_x nanoparticle catalyst had a low overpotential of only 28 m V under alkaline.Also,the catalyst had the lowest Tafel slope compared to the control sample,indicating its fastest reaction kinetic rate.In addition,after normalizing the current density by electrochemical specific surface area,the catalyst still exhibited the lowest overpotential,exhibiting its best intrinsic activity.Moreover,the Ni-Ni Mo O_x nanoparticle catalyst could run stably for 340 h at the current density of 10 m A cm^-2.They were also tested under simulated commercial and commercial conditions,for both of which excellent electrocatalytic activity and robust stability were demonstrated,infering that the samples were promising for commercial applications.This study supplied a new idea for the preparation of electrocatalysts for water splitting in large scale applications.Compared with the two-electron transfer process of HER,OER process involving four-electron transfer is a much slower kinetic half-reaction.More difficultly,the concentration of the intermediate reactants under neutral electrolyte is pretty low,leading to the reaction process necessary to be driven by a higher potential and thus resulting in even high overpotential and poor stability.Herein,a noble-metal-free Fe-modified cobalt-nickel nanorod（Fe-Co Ni O（OH））catalyst was prepared by a simple one-step hydrothermal method.With the help of electron microscopy and spectroscopic characterization,it is found that the introduction of Fe modulated the electronic structure and promoted the formation of high valance metal sites,which was favorable for the adsorption of intermediate reactants to enhance the water splitting.The OER performance of the catalyst was investigated in 1 M PBS solution（p H=7）,and the overpotential of the catalyst was only 411 m V at current density of 10 m A cm^-2.Meanwhile,compared to the control samples,the Fe-modified Co Ni nanorods catalyst had the lowest Tafel slope,indicating that it had the fastest reaction kinetic rate.Finally,at the current density of 10 m A cm^-2,the catalyst could run stably for 160 h,which was better than that of most reported non-noble OER catalysts.This work will provide reference for the preparation of electrocatalysts in large-scale electrolysis of water under mild condition.