Preparation And Electrocatalytic Performance Of Self-supporting Nickel Based Composite Materials

With the development of scientific progress,traditional fossil fuels cannot meet people’s needs due to their limited reserves and environmental pollution.It is urgent to find new clean and renewable alternatives to fossil fuels.Hydrogen is widely recognized as the most promising and preferred contemporary energy substitute due to its high energy capacity and environmentally friendly emissions.Electrocatalytic water decomposition is a clean energy and effective hydrogen production technology.Electrocatalytic cracking of water is considered to be a necessary and promising energy conversion technology for the development of clean and sustainable energy.Theoretically,a minimum voltage of 1.23 V is required to achieve overall water decomposition,which is higher than the potential of commercial electrolytic batteries.Currently,the most effective electrocatalysts for hydrogen precipitation reaction（HER）and oxygen precipitation reaction（OER）are Pt-based materials and Ru O₂/Ir O₂,respectively.However,their scarcity and high price severely restrict their widespread commercial usage.Efficient non-noble metal catalysts are required for clean energy technologies.Among many material systems used to study catalysts,transition metal chalcogenides have been widely studied for water decomposition due to their low cost,high conductivity,and ease of preparation through sulfurization or selenidation reactions.Among these catalysts,nickel based multiphase composites,especially Ni S_xmaterials with excellent and efficient activity for HER and OER,have been extensively studied through method adjustment and complex multicomponent manufacturing.In this paper,a series of transition metal sulfide micro/nanomaterials were prepared by various methods（e.g.hydrothermal method,calcination method,electrodeposition method）using nickel foam with large specific surface area as substrate,and their electrochemical hydrogen/oxygen precipitation performance under alkaline conditions was investigated,and the crystal structure and elemental composition of the catalysts were analyzed by a series of characterization tools to further explore their electrocatalytic reaction mechanism.The main research results are as follows:（1）A 3D sea urchin-like W₁₈O₄₉/NF was prepared using tungsten hexachloride as raw material by a one-step hydrothermal method,and then S-W₁₈O₄₉/NF was obtained by doping with S source.Then,the catalytic performance of OER,HER,and OWS with alkaline conditions will be tested respectively.The results demonstrated that S-W₁₈O₄₉/NF,which has the smallest tafel slopes(21m V·dec^-1and 92m V·dec^-1),only needs 214 and 131m V to achieve the current density of 10m A·cm^-2toward OER and HER in alkaline systems.As for overall water splitting（OWS）,the required overpotential of the catalyst at 10m A·cm^-2is only 1.57V.In the stability test lasting for60hours,S-W₁₈O₄₉/NF also has good electrocatalytic activity.Its excellent catalytic activity is attributed to the doping of S source,which enhances the conductivity of W₁₈O₄₉/NF,accelerates its charge transfer rate,increases the electrochemical active area,and also increases more active vacancies（S defects and O defects）in S-W₁₈O₄₉/NF.（2）Ni₂S₃was in-situ grown on foam nickel as substrate and Ni source,and then graphene oxide was compounded with Ni₂S₃-r GO/NF by a simple hydrothermal method.The effects of different experimental conditions on the OER properties of the synthesized Ni₃S₂-r GO/NF were studied.The results showed that the optimal experimental conditions for the synthesis of Ni₃S₂-r GO/NF were as follows:the amount of sulfur powder was 1.0 g,the reaction temperature was 300℃,and the annealing rate was 5℃·min^-1.Physical tests show that the prepared Ni₃S₂has a micron scale structure,and the introduction of r GO increases the conductivity and active sites of the catalyst,while also inhibiting the growth of Ni S,which has a refining effect on the Ni₃S₂crystal.However,the finer Ni₃S₂microspheres and the synergistic effect with graphene oxide greatly increase their electrocatalytic activity.（3）First,Ni WO₄nanospheres were directly grown on foam nickel substrate using Ni SO₄·6H₂O and Na₂WO₄with molar ratio of 1:1 as nickel source and tungsten source by simple hydrothermal method,and then Ni WO₄/Ni Fe-LDH was obtained by combining hydroxide with Ni WO₄nanospheres using electrodeposition in traditional three electrode system.By comparing the OER catalytic performance of Ni WO₄/Ni Fe-LDH synthesized at different deposition times in 1.0M KOH,it can be seen that the optimal deposition time is 45 minutes,and excessive deposition time can lead to reduced catalytic performance of the material.The excellent catalytic activity stems from the large specific surface area of Ni Fe-LDH and the good conductivity of Ni WO₄,which accelerate electron transport,while the excellent stability stems from the stable structure of Ni Fe-LDH and the strong synergy between them.