Design,Synthesis And Performance Of Transition Metal-based Water Splitting Electrocatalysts

The energy shortage and environmental pollution caused by the massive consumption of fossil fuels have severely restricted sustainable development of human society,which prompt researchers to find renewable clean energy and energy conversion technologies to solve the above major problems.As a renewable energy with high energy density and no pollution of combustion products,hydrogen is considered to be an energy carrier with great potential to substitute fossil fuels.Hydrogen energy production from electrolytic water technology with the advantages of high clean conversion efficiency and mild conditions,is one of the effective ways to prepare sustainable hydrogen.Due to the presence overpotential of oxygen evolution and hydrogen evolution reactions in this technology,the operating voltage required in practice is much higher than theoretical requirement,increasing the energy consumption.Thus,the development of cheap,efficient and stable electrolyzed water electrocatalysts is the key to solving the above problems,and has important scientific value and significance.In this dissertation,we devote to develop the transition metal-based catalytic materials with abundant reserves,low cost and high efficiency,and design and regulate the electronic structure and morphology of catalysts by metals doping and heterostructures.The obtained self-supporting bifunctional catalyst with high-efficiency oxygen evolution and hydrogen evolution reaction shows efficient electrocatalytic overall water splitting activities with a low cell voltage by assembling a two-electrode system.The main research contents of this dissertation are as following:1.A 3D CoO/Co4N/NF heterostructure catalyst electrode was developed.The heterostructure interface of CoO and Co4N was constructed and the influence of heterostructure interface on the electronic structure of CoO and Co4N was studied.The problems of conductivity,electron transport,and electrocatalytic activity were solved,which promoted the electrocatalytic water splitting kinetics.The CoO/Co4N/NF heterostructure catalyst shows excellent bifunctional electrocatalytic oxygen and hydrogen evolution reaction activities in neutral electrolyte.Using CoO/Co4N/NF as direct catalytic electrodes,the CoO/Co4N/NF exhibits high-efficiency overall water splitting activity in a neutral electrolyte,requiring a low cell voltage of 1.79 V to drive a current density of 10 mA cm-2.Moreover,CoO/Co4N/NF heterostructure catalyst shows excellent durability.2.Using 3D strutted graphite SG as a current collector with large surface area,excellent electrical conductivity,and mechanical property,NiFeP ultrathin nanosheets were loaded on SG by hydrothermal-low-temperature-phosphorization reaction,and self-supporting 3D NiFeP/SG porous monolith electrode were prepared.The effects of morphology and iron doping on the electronic structure of Ni2P were investigated.It was found that the iron incorporation modulates the shifted-up d states,and the NiFeP ultrathin nanosheet morphology and the 3D porous structure of the SG collector afford high concentration of active sites on the surface and facilitate the improvement of electrocatalytic performance.As a self-supporting catalytic electrodes,the 3D NiFeP/SG exhibits excellent electrocatalytic oxygen evolution,hydrogen evolution reaction,overall water splitting activities and excellent electrochemical durability in alkaline electrolyte,requiring low overpotential of 218 mV,125 mV and low cell voltage of 1.54 V to achieve a current density of 10 mA cm-2,respectively.In additiona,NiFeP/SG monolith electrode shows excellent gravimetric electrocatalytic activities.This material opens a way to prepare lightweight catalytic electrode and has potential applications in electrochemical energy storage and conversion.3.A 3D Ni3N/Ni0.2Mo0.8N/MoO3/SG monolith electrocatalytic electrode was prepared by hydrothermal-ammonolysis reaction with SG as the substrate.Ni3N/Ni0.2Mo0.8N/MoO3 has nanorod-like morphology.Due to the synergistic effect of multi-components in Ni3N/Ni0.2Mo0.8N/MoO3,the high conductivity and 3D porous structure of the SG substrate,the prepared 3D Ni3N/Ni0.2Mo0.8N/MoO3/SG monolith electrode shows excellent OER and HER catalytic activities,with low overpotential and Tafel slope,large electrochemical surface area and low resistance,and excellent stability in alkaline electrolyte.When used 3D Ni3N/Ni0.2Mo0.8N/MoO3/SG electrode as the anode and cathode of overall water splitting,it requires a low cell voltage of 1.53 V at 10 mA cm-2 for catalyzing overall water splitting.These results indicate that this electrode is a potential electrocatalytic overall water splitting catalyst.