Construction Of Ni-based Heterostructure Electrocatalysts For Electrochemical Water Splitting And Performance Investigation

Faced with the energy and environmental crisis,the utilize of electrolyzed water technology to develop clean and sustainable hydrogen energy is the key to alleviate the problems.Therefore,the development of efficient,stable,and low-cost electrocatalysts has become a research hotspot to improve the efficiency of water electrolysis for hydrogen production.Therefore,this paper aims to improve the performance and stability of the catalyst through various strategies to adjust the electronic structure and catalytic reaction energy barrier of the catalyst,thereby improving the energy conversion efficiency of water electrolysis for hydrogen production.In this paper,multi-strategies including doping engineering,heterostructure engineering and defect engineering were used to tune the intrinsic activity of Ni-based catalyst.And excellent and stable Ni-based alkaline water electrolysis catalysts were synthesized,which were also studied the mechanism of catalytic reaction process by in situ Raman spectroscopy.The 9details are as follows:（1）In view of the insufficient electrocatalytic oxygen evolution reaction（OER）performance of heterostructured composed of two transition metal catalysts,This article designed an in situ electrochemical conversion method to synthesize higher OER performance heterostructured electrocatalysts.Firstly,This article synthesized a precatalyst Ni₉S₈/Ni₃S₂,and then utilized the unstable nature of Ni₉S₈ in alkaline and OER reaction potentials to perform in situ convert on Ni₉S₈/Ni₃S₂.XPS and in situ Raman indicated that Ni₉S₈ was converted to nickel hydroxide or nickel oxide and then oxidized to form amorphous nickel oxyhydroxide（Ni OOH）at OER potential.This process formed an amorphous Ni OOH/Ni₃S₂ heterostructured catalyst with abundant Ni³⁺and promoted the charge transfer between Ni OOH and Ni₃S₂.The non-activated Ni₃S₂ group also improved the conductivity of the catalytic material,so the in-situ generated heterostructured catalyst had excellent OER catalytic performance.（2）The electrocatalytic hydrogen evolution reaction（HER）of single-metal catalyst has the problems of low activity,few active sites and high reaction energy barrier.To solve these problems,based on the method of constructing a new heterostructure through electrochemical partial phase transition in（1）,This article have taken metallic nickel as the starting point and partially converted metallic nickel into nickel hydroxide by electrochemical conversion,forming a Ni^（0）/Ni（OH）₂/NF heterostructured HER electrocatalyst with rich Ni^（0）-Ni（OH）₂ heterointerface.The Ni^（0）-Ni（OH）₂ heterointerfaces could provide a large number of active sites and optimize the Gibbs free energy of H*adsorption,therefore endowing the Ni^（0）/Ni（OH）₂/NF heterostructured with excellent catalytic activity and stability.In situ Raman spectroscopy revealed the reduction and regrowth process of Ni（OH）₂ andindicated that the Ni^（0）-Ni（OH）₂ heterointerface was the catalytically active center.（3）In view of the problem that it is difficult to realize the synthesis of a bifunctional catalysts for both HER and OER with a single strategy,This article have combined the electrochemical conversion strategies in（1）and（2）and elemental doping strategy to synthesize an excellent and stable bifunctional electrocatalyst.Firstly,a Cu and Fe co-doped Ni catalysts（Cu,Fe-Ni/NF）was synthesized,which then underwent partial oxidation to form Cu,Fe co-doped Ni/Ni（OH）₂ heterostructured catalyst（Cu,Fe-Ni/Ni（OH）₂/NF）by electrochemical oxidation.XPS and in situ Raman spectroscopy showed that the Cu and Fe co-doping optimized the electronic structure of the catalyst by decreasing the oxidation state of Ni in the catalytic process,which thereby reduced the energy barrier of electron transfer and improved the oxygen production efficiency.In addition,the Ni/Ni（OH）₂ heterostructured provided abundant Ni^（0）-Ni（OH）₂heterointerfaces,hence exposing a large number of catalytic reaction centers for HER.Meanwhile,Cu doping reduced the crystallinity of the catalyst and made more active sites expose.In situ Raman spectroscopy further indicated that Fe doping stabilized the Ni^（0）-Ni（OH）₂ heterointerfaces,and thus Cu,Fe-Ni/Ni（OH）₂/NF exhibited an outstanding and ultra-stable HER performance.The bifunctional properties of Cu,Fe-Ni/Ni（OH）₂/NF catalyst also enabled it to show excellent and stable electrocatalytic performance for overall water electrolysis.