Construction Of Dual-Element Decorated Transition Metal-Based Nanostructured Electrocatalysts And The Study Of Their Electrolytic Water Performance

The massive consumption of non-renewable energy sources has exacerbated the energy crisis and environmental pollution,and it is increasingly urgent to replace traditional fossil energy sources with renewable and clean energy sources.Hydrogen is the ideal renewable energy source,and electrolytic hydrogen is the most efficient way to produce pure hydrogen,Pt-based materials and Ru-based materials are the most superior electrocatalysts for HER and OER respectively,but due to their high prices,they are difficult to use in large quantities in production.Transition metals such as Fe,Co,Niand their compounds are cheap and easy to produce,and their unique outer electron structure and strong redox properties give them unique catalytic efficacy for the electrocatalytic decomposition of water,which has excellent prospects for application in the electrolysis of water for hydrogen production.In this thesis,a series of transition metal-based nanomaterial electrocatalysts were prepared and a double doping strategy was employed to enhance the HER,OER and total water decomposition performance of the transition metal-based materials.The details of the study are as follows:1.The Cr and Fe-co-doped two-dimensional mesh-shaped porous nanosheet structure of cobalt phosphide catalysts（Mesh-Cr-Fe-Co P NSs）was successfully prepared by a two-step solvent thermal-gas phase phosphorylation method.The prepared catalyst electrode materials were analysed for their microscopic morphology,chemical valence and elemental composition using various characterisation methods.The optimal electrocatalytic performance was demonstrated by tuning the amount of Cr and Fe doping.The optimal Cr/Fe co-doped Co P（Mesh-Cr-Fe-Co P NSs）synthesized in 1 M KOH exhibited significant catalytic activity for HER and OER with overpotentials of 102 and 262 m V at a current density of 10 m A cm^-2,respectively,showing excellent catalytic performance for HER and OER,which was significantly better than Mesh-Cr-Fe-Co P NSs,Mesh-Fe-Co P NSs,Mesh-Cr-Co P NSs,Mesh-Co P NSs,Bulk-Co P and Co P-based HER and OER catalysts reported in the literature,while Mesh-Cr-Fe-Co P has excellent catalytic performance for total hydrolysis,with the application of 1.53 V The excellent electrocatalytic performance of Mesh-Cr-Fe-Co P was attributed to the introduction of Cr and Fe to optimise the electron density of Co P,lowering the aqueous dissociation energy barrier,accelerating electron transport and effectively enhancing electrocatalytic performance.2.The Cr and N double doped Fe₃O₄ electrocatalyst（Cr-Fe₃O₄-N/NF）was prepared by static infiltration and calcination using nickel foam as conductive substrate.The prepared catalyst electrode materials were analysed for their microscopic morphology,chemical valence and elemental composition using various characterisation methods.Under alkaline conditions,the synthesized Cr-Fe₃O₄-N/NF has significant catalytic activity for OER and HER.At the current density of 10 m A cm^-2,the overpotential is 218 m V and 95 m V,respectively,showing excellent catalytic performance for OER and HER.Significantly better than Fe₃O₄-N/NF,Cr-Fe₃O₄/NF,and Fe₃O₄/NF.Meanwhile,the water decomposition system using Cr-Fe₃O₄-N/NF as anode and cathode can provide a current density of 10 m A cm^-2 at 1.53 V,which is superior to the electrolytic cell consisting of Pt/C and Ru O₂.In addition,the long-term durability of the catalyst at 50 m A cm^-2 constant current for up to 50 h is significantly better than most reported Fe based catalysts.The results of catalytic mechanism study showed that Cr and N doping increased the number of active sites of catalytic electrode materials.At the same time,the charge transfer resistance is reduced,the charge transfer is promoted and the reaction kinetics is accelerated,thus synergistically improving the OER and HER performance of the catalyst.3.The Cr and N-co-doped NiSe₂ nanosheet array（Cr-NiSe₂-N/NF NSs）was synthesized by using nickel foam as carrier.The prepared catalyst electrode materials were analysed for their microscopic morphology,chemical valence and elemental composition using various characterisation methods.The obtained Cr-NiSe₂-N/NF NSs catalyst showed excellent Bi-functional catalytic activity for both HER and OER,with an overpotential of 137 and 253 m V at10 m A cm^-2 and 20 m A cm^-2,respectively.The decomposition voltage of Cr-NiSe₂-N/NF NSs is1.56 V at 10 m A cm^-2.In addition,the overpotential of the catalyst did not decrease significantly after continuous electrolysis for 100 h under high current density,indicating that the catalyst has excellent stability.The results of catalytic mechanism research indicate that the doping of Cr and N elements in NiSe₂ nanoplates leads to the formation of a large number of vacancy defects,which may effectively reduce the energy barrier for H₂O adsorption and optimize the adsorption energy of HER and OER intermediates.In addition,the Cr-NiSe₂-N/NF NSs nanosheet array on the nickel foam has a high electrochemical active area,which is conducive to charge and electrolyte mass transfer,thus further enhancing the electrocatalytic performance.