| Significant concerns have been raised about the sustainability of global energy as the world’s population grows,energy demand increases,and the effects of global warming.Hydrogen（H2）is considered an ideal and efficient alternative as a clean energy fuel with high energy density,zero carbon emissions and renewable properties.Electrochemical water cracking is a promising strategy in this regard,water molecules are split into hydrogen and oxygen（O2）by electrochemical hydrogen evolution reactions（HER）and electrochemical oxygen evolution reactions（OER）.Precious metal-based catalysts,such as Pt-based materials（for HER）and Ru/IR-based materials（for OER）,have attracted a lot of attention due to their efficient electrocatalytic properties in increasing reaction rates and reducing overpotential.However,high prices and scarce reserves limit their further application in practice.This drives the urgent need for efficient electrocatalysts.Good electrical conductivity,suitable energy band structure and relatively excellent chemical stability are all excellent characteristics of suitable alternative catalytic materials.Therefore,the research content discussed in this paper is to construct transition metal-based nanomaterials using structural design strategies,and improve the overall number of active sites and the intrinsic properties of each active site of the catalyst by centering on heterogeneous interfaces,atomic doping,defect engineering,etc.,to improve the water decomposition performance of transition metal-based catalysts.The following studies have explored the origin of electrochemical activity at non-homogeneous interface in electrocatalytic processes and the influence of heterogeneous interface charge reconfiguration on HER and OER processes through physical and chemical characterization of material morphology,structure and composition combined with density functional theory calculation（DFT）,providing guidance and direction for the design of highly active transition metal catalysts in the future:（1）By a simple chemical synthesis method,three-dimensional nanostructured flower heterostructures（Mo S2@Co-MOF@Co Al-LDHs/NF）electrocatalytic materials supported by nickel foam（NF）have been successfully obtained.The unique heterogeneous structure can greatly enrich the catalytic sites and accelerate the charge transfer.Thanks to the synergistic effect between components,HER process shows excellent electrocatalytic activity.In 1.0 M KOH solution,only 96 m V overpotential can drive the current density of 10 m A cm-2,and the Tafel slope is 73.53 m V dec-1.At the same time,HER low decay rate and strong electrochemical durability of catalyst are also satisfactory.Therefore,an environmentally friendly and economical electrocatalytic material preparation method is proposed in this paper,which provides more new ideas for the design and preparation of transition metal-based hydrogen evolution materials in the future.（2）Mott-Schottky heterostructure（Mo-Ni Co P@MXene/NF）nanomaterials were cleverly designed by combining metallic phase MXene with N-type semiconductor Ni Co P.The heterojunction with self-driven charge transfer interface can promote the metal abundance and electron redistribution of the catalyst,while Mo doping can effectively adjust the electronic structure of Ni Co P,increase the electroactive sites,and improve the natural activity of each site.The electron transfer rates of the active center and d-band center near the Fermi level were optimized.As expected,the synthesized three-dimensional wrinkled rough"triangle plum"flower-like structure Mo-Ni Co P@MXene/NF exhibited excellent OER and HER electrocatalytic properties(requiring overpotentials of 96 m V and 290 m V respectively to drive current densities of 10 m A cm-2).More importantly,with Mo-Ni Co P@MXene/NF as a dual electrode,a low overpotential of only 1.56 V is sufficient to drive a current density of 10 m A cm-2 in a dual electrode configuration,which is significantly superior to other dual-function electrocatalysts.Therefore,the proposed strategy provides a new idea for the design of efficient transition metal-based bifunctional electrocatalysts using cationic doping and Mott-Schottky heterogeneous structures.（3）Here,using Prussian blue analogues（PBA）as precursors,sodium borohydride was used to reduce Co Fe Se supported on MXene matrix with excellent electrical conductivity and hydrophilicity,and composite structural nanomaterials(VSe-Co Fe Se@MXene/NF)rich in selenium vacancy were successfully prepared at room temperature.The Se vacancy accelerates the interfacial charge transfer,optimizes the electron density on Co Fe Se,and increases the adsorption capacity of water and reduces the dissociation energy barrier of water.Thanks to the strong chemical and electronic synergies between the structures,the material exhibits excellent activity as an economical and efficient bi-functional electrocatalyst.The synthesized VSe-Co Fe Se@MXene/NF electrocatalysts OER and HER showed excellent activity with low overpotential of 283 m V and 67 m V at 10 m A cm-2,respectively.At the same time,DFT calculations show that the introduction of Se vacancy on the Co Fe Se surface can regulate the change of Gibbs free energy between different HER/OER steps,thus significantly reducing the overpotential.Therefore,this paper provides a new idea and direction for better understanding and design of excellent bifunctional electrocatalysts. |
