Research On Electrocatalytic Properties Of Ni Based Nanomaterials By Modification Assisted With Plasma

Nowadays,hydrogen is considered as a renewable and clean energy.Among many energy conversion technologies,the electrocatalytic water splitting to produce hydrogen has been widely studied as an efficient and pollution-free approach.The electrocatalytic water splitting mainly involves hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?.Noble Pt based materials are the best HER electrocatalysts,while noble Ru based/Ir based materials are the best OER electrocatalysts.However,these noble metal based electrocatalysts are expensive and scarce in resources,which seriously limits their wide applications.Ni based electrocatalysts have become the promising candidates because of the advantages of low cost,diverse compostion,rich chemical valences and good elec trocatalytic activities.To meet the needs of practical application and to be closer to the electrocatalytic performances of precious metals,the research focuses on improving the intrinsic activities of Ni based electrocatalysts for further improving the electrocatalytic performances.Based on this,this paper uses the plasma surface modification to make vacancies on the surface of Ni based electrocatalysts,and then realizes the improvement of electrocatalytic performances by the complex modification of elements doping with vacancy assist.The influence mechanism of the complex modification on the microstructure,surface state and electronic structure of electrocatalysts is clarified,and the strengthening mechanism of electrocatalytic performances by the complex modification is clarified,which provides theoretical basis and experimental support for develop ing new Ni based electrocatalysts with high efficiency.Firstly,a new method to improve the electrocatalytic properties of Ni based nanomaterials by oxygen vacancy assisting elements doping was proposed.Oxygen vacancy was produced on Ni Co₂O₄ surface by plasma surface modification,and then S doping was realized by immersing in Na 2S solution.The results showed that S doped Ni Co₂O₄ by oxygen vacancy assist had more Co3+,and Co3+ had the larger binding energy with water molecular,which promoted the four-electron transfer process in OER process,and thus leading to higher OER activities.In addition,the theoretical calculation results showed that there were new electronic states in the conduction band of S doped Ni Co₂O₄ by oxygen vacancy assist.And the density of states at the edge of the conduction band significantly increased,indicating that more electrons participated in the catalytic reaction,which was conducive to improving the catalytic performances.The electrochemical results showed that the S doped Ni Co₂O₄ by oxygen vacancy assist exhibited the excellent electrochemical performances.At the current density of 10 m A cm-2,the overpotentials for HER and OER were only 137 and 256 mV,respectively.When serving as bifunctional electrocatalysts,it also showed the good electrocatalytic activity.At the current density of 10 m A cm-2,the voltage for overall-water-splitting was only 1.63 V.To increase the number of active sites and improve the intrinsic activity,a new mode of vacancy coupled anion doping was proposed,thus P vacancy coupled S doping was introduced into NiCoP by plasma surface modification.The results showed that the synergistic effect of P vacancy coupled S doping led to the increase of the number of active sites exposed in NiCoP.And the surface chemical states were also optimized and the conductivity was improved.The theoretical calculation showed that the synergistic effect of P vacancy coupled S doping enhanced the conductivity,and optimized the hydrogen adsorption free energy of NiCoP that lowered from-0.53 e V into-0.36 e V,indicating the improved intrinsic activities.At the current density of 10 m A cm-2,the overpotentials of P vacancy coupled S doped NiCoP were only 88 mV and 264 mV for HER and OER,respectively.When serving as bifunctional electrocatalysts,it only required an overall-water splitting voltage of 1.60 V to reach the current density of 10 m A cm-2.In addition,Se vacancy coupled P doping was introduced into NiSe₂ by the same way.The electrochemical results showed that the HER performances were greatly optimized by Se vacancy coupled P doping.Theoretical calculations revealed that the interaction of P doping and Se vacancy played a significant role in lowering the hydrogen adsorption free energy in Ni,Se and P sites,confirming the promoted intrinsic HER activities.To further improve the electrocatalytic water-splitting performances,a new mode of vacancy coupled cation doping was proposed,thus P vacancy coupled V doping was introduced into NiCoP by plasma surface modification.The results showed that V doping increased the electrochemical active surface area and adjusted the electronic density of the active site center,while P vacancy was beneficial to the exposure of the active site,enhanced the electronic interaction and promoted the electron transfer.The electrochemical results showed that P vacancy coupled V doped NiCoP exhibited the excellent electrochemical performances.At the current density of 10 m A cm-2,the overpotentials were only 58 and 246 mV for HER and OER,respectively.When serving as bifunctional electrocatalysts,it also showed the good electrocatalytic activity and long-term stability.When the current density was 10 m A cm-2,the overall-water-splitting voltage of P vacancy coupled V doped NiCoP was only 1.55 V.Based on the above researches,a new enhancing electrocatalytic performance s by vacancy defect activated heterogeneous interface is proposed to give full play to the advantages of defects,thus P defect boosted Ni2P/Cu3 P electrocatalysts was prepared by plasma surface modification.The results showed that abundant P defects were beneficial to increase the exposure of active sites,and abundant Ni2P/Cu3 P heterointerfaces were beneficial to regulate the electronic structure.Therefore,the P defects and heterointerfaces worked together to enhance the electrocatalytic activities.The electrochemical results showed that the overpotentials of P defect boosted Ni2P/Cu3 P in HER and OER are 38 and 90 mV lower than those in Ni2P/Cu3 P,respectively.In addition,the research syst em was further extended to S defect boosted MoS₂/Ni S2.The results showed that rich S defects provided abundant electroactive sites,and Mo S 2/Ni S2 effectively modified the electronic interaction,thus leading to the promoted electrocatalytic activities.Electrochemical tests show that S defect boosted MoS₂/Ni S2 showed the excellent electrocatalytic performances in HER,OER and over allwater splitting.