Synthesis Of 3D Transition Metal Based Array Catalysts And Their Application In Electrocatalytic Water Splitting

Pollution caused by excessive use of fossil fuels has brought great distress to our daily life and environment.Hydrogen is considered to be one of the new and clean energy sources that is potential to replace fossil fuels.The rapid development of electrocatalytic water splitting technology increases the possibility for hydrogen energy to be used on large scale in practice.Water splitting generally consists of two half reactions,involving hydrogen evolution reaction?HER,cathode?and oxygen evolution reaction?OER,anode?.Exploring non-noble metal catalysts for these two half reactions has become the focus of current research.Transition metals are rich on earth,low in cost,and their adjustable electronic state can reduce the thermodynamic reaction barrier in the process of electrocatalytic water splitting.These are conducive to enhance the electrocatalytic efficiency,and also benefit the catalyst design and preparation.In this dissertation,the transition metal-based materials are studied for the water splitting reaction.Anion-doping strategy and 3D conductive substrate are employed to improve the catalytic performance.At the same time,in order to reduce the cost of materials,low energy consumption conditions such as room temperature are applied for the sample synthesis,which is benefit for the industrial production and promotes the development of hydrogen energy.First,P doped Ni₃S₂ nanosheet arrays were successfully obtained on the nickel foam?NF?substrate by hydrothermal method and subsequent annealing treatment.Unlike cation doping,the incorporation of anion P element can effectively adjust the electronic state of Ni₃S₂ without changing its crystal structure,increase the carrier concentration,activate and expose more active sites,and thus can directly promote the electrocatalytic efficiency of the material.In addition,the array structure on the 3D porous conductive substrate ensures the rapid transfer of electrons during the electrocatalytic process.The fast diffusion of reactive species and rapid release of the generated gas can keep the active sites exposed to the electrolyte and reactants,thereby enhance the overall electrocatalytic efficiency.After that,one new and clean NF was immersed in a solution containing various metal ions at room temperature,and the nanosheet arrays were obtained directly on the NF substrate,caused by the etching effect of Fe³⁺on NF and the co-precipitation process of transition metal ions.Rapid synthesis at low temperature can inhibit the excessive growth of nanosheets in the initial stage of crystallization,make the three ions of Fe,Co,and Ni evenly distributed and closely connected,and work together to improve the catalytic efficiency.The obtained Fe-Co-Ni hydroxide electrode requires only 212 mV overpotential to reach a current density of 10 mA cm^-2 during OER in 1.0M KOH electrolyte solution,overperforming most of analogous catalytic materials reported so far.Finally,another NF substrate was immersed at room temperature,in a mixed solution containing HCl and CuSO₄ to generate Ni-CuCl intermediates.Afterwards,the Ni-CuCl was converted into Ni-CuO as OER catalysts via an in-situ electrochemical oxidation process.Ni-CuO was then immersed in the Na₂S solution,which was converted to Ni-CuO-S by partial sulfidization for HER catalysis.The doped Ni atom can effectively activate the CuO matrix,increasing the carrier concentration.It is found that the Cu²⁺rather the common Ni²⁺ion is the active site.When using Ni-CuO and Ni-CuO-S as the anode and cathode electrodes,respectively,the whole water splitting is realized,and their performance is better than commercial Pt/C and RuO₂,associated with good stability.