Noble-metal-free Ni₃C As Co-catalyst On LaNiO₃ With Enhanced Photocatalytic Activity

With the development of social economy and industrial industries,environmental pollution and energy shortages have become increasingly serious in recent years.Hydrogen production by photocatalytic water splitting represents one of the most promising approaches for energy storage and clean fuel generation.With the continuous in-depth research on it,researchers have tried a variety of strategies.Among them,loading co-catalyst materials to construct a composite photocatalyst has become a relatively new strategy with great potential.The co-catalyst can significantly improve the carrier separation and transport ability of the composites.So far,it has been proven that precious metals are the most efficient co-catalyst about the hydrogen evolution reactions（HER）.However,precious metals are expensive and have low abundance in the earth,which limits their use in large-scale applications.Therefore,there is an urgent need to develop a low-cost and high-efficiency co-catalyst for photocatalytic water splitting,which is also a popular research direction.Transition metal carbides（TMCs）have noble metal-like electronic structure and low production cost.There have been a large number of reports on the use of non-noble metal co-catalyst TMCs combined with g-C₃N₄ or sulfide materials.Therefore,the construction of new composite photocatalysts with TMCs and other types of semiconductors has attracted our great attention.Oxide semiconductor materials with excellent photocatalytic performance,low production cost and environmental friendliness are candidates for large-scale application of photocatalytic hydrogen production.Among them,the perovskite-type oxide LaNiO₃ nanomaterials have a narrow band gap structure and a wide light absorption range,and there is no report on the use of TMCs on LaNiO₃ nanomaterials for photocatalytic hydrogen production.In this study,we first explored the preparation of larger-sized LaNiO₃ NPs based on the solvothermal method followed by annealing and recrystallization.On the basis of obtaining LaNiO₃ NPs with a good degree of crystallization,LaNiO₃-Ni₃C composite samples were successfully synthesized by the secondary growth method.Loading 3wt%Ni₃C on LaNiO₃NPs,the H₂ production rate is increased about 5 times and 2 times compared with pristine LaNiO₃ nanoparticle and 1wt%Pt loaded LaNiO₃ nanoparticle.The structure,composition,and morphology of the Ni₃C loaded LaNiO₃ NPs are characterized by XRD,XPS,SEM,and HRTEM.The effects of loading different contents of Ni₃C on the photocatalytic progress are investigated by UV-Vis,EIS test,photocurrent test,electrocatalytic hydrogen evolution test,and Tafel analysis.We found that the charge separation performance and H₂ precipitation kinetics could be improved by increasing the content of Ni₃C from 1wt%to 3wt%.Then,with the further increase of Ni₃C loading from 4wt%to 6wt%,the photocatalytic performance showed a weakening trend.Based on the detailed characterization of LaNiO₃-6wt%Ni₃C composite sample,this negative effect can be attributed to the surface decomposition of LaNiO₃ nanoparticles caused by the reducing carbon source in the process of chemical loading of Ni₃C,and the reducing corrosion effect caused by the loading of Ni₃C can be suppressed by adjusting the content of Ni₃C.In this paper,a simple method to prepare highly efficient LaNiO₃-Ni₃C composite nanoparticles was summarized.Compared with the pure LaNiO₃ sample,the photocatalytic hydrogen production performance of the composite was improved by 5times.In addition,the mechanism of improving the photocatalytic performance of LaNiO₃ samples by loading certain amount of Ni₃C nanoparticles was studied,and the negative effects of reducing carbon source on the performance of the samples during loading were further studied.This work indicates that with proper content using TMC as cocatalyst with oxide photocatalyst can be a promising strategy for designing low cost,high efficient,and long sustainability H₂ evolution photocatalyst,without concerning the corrosion from the reductive carbonous precursors in the loading process.