Controllable Preparation Of Nickel Phosphide-based Flexible Electrode Toward Eldctrocatalytic Water Splitting

Hydrogen energy,as a recognized green energy,has a broad development prospect due to its high energy density and renewable performance.Electrocatalysis for water splitting is a clean and efficient way to produce hydrogen energy and obtain high purity oxygen.Meanwhile,the cost of the IrO₂ and Pt-based highly active catalysts hinder the large-scale applications.Based on this,it is significant to explore an efficient and accessible catalyst for water splitting reaction.As nickel phosphide has a pretty catalytic activity and good stability under full pH conditions,the catalyst with excellent electrocatalytic total water splitting reaction performance is elaborately designed and has important research significance.However,the intrinsic activity of nickel phosphide catalyst cannot be compared with the noble metal catalysts.Therefore,it is of great value to improve the catalytic activity by adjusting the morphology and composition of catalysts.This theis aims to prepare a highly active,long-term stable electrocatalytic total water splitting catalyst.Its research focuses on the relationship between the morphology,the composition of nickel phosphide and the choice of substrate and catalytic performance.The main research contents and conclusions are as follows:（1）We propose a simple method for large-scale preparation of ultra-small nano-phosphides.Graphene oxide（GO）and foamed nickel（NF）undergo an interfacial redox reaction in water,and then perform simple phosphating.On the foamed nickel,ultra-small nickel phosphide nanoparticles（Ni₂P/RGO@NF）supported by reduced graphene oxide can be obtained.This self-supporting Ni₂P/RGO@NF catalyst has a good three-dimensional nanostructure,excellent electrical conductivity and high density of ultra-small nickel phosphide particles（24,000 per square micrometer）.Electrocatalytic total water dissipation experiments show that only 1.58 V and 1.68 V low voltages are needed to achieve a current density of 10mA·cm^-2 in alkaline and neutral electrolytes.This catalyst has excellent electrocatalytic water splitting performance and long-term stability under alkaline and neutral conditions（electrolytes with pH values of 14 and 7 respectively）.In addition,a sample of ultra-small cobalt phosphide（CoP/RGO@CF）supported on reduced cobalt oxide was prepared on the cobalt foam by the same method.The experiments prove that this method is a general method for manufacturing ultra-small transition metal nanoparticle self-supporting electrocatalysts.（2）By doping appropriate amounts of molybdenum and copper into the Ni（OH）₂precursor,the morphology of the catalyst can be effectively adjusted to increase the specific surface area of the catalyst.Then low-temperature phosphating treatment could make that Ultra-small nanoplate modified nanorods are evenly grown on the surface of nickel foam.Experimental data show that when the two elements of Mo and Cu are doped at the same time,the conductivity of the catalyst is increased,and the content of highly active Ni^Ⅲ/Ⅱis obviously increased,and the inherent activation barriers of the HER and OER is reduced.Under alkaline conditions,this catalyst only needs a low voltage of 1.46 V to achieve a current density of 10 mA·cm^-2,and has excellent electrocatalytic water splitting performance and stability.（3）Under acidic conditions,nickel foam substrates are not stable during the reaction,therefore,other acid-resistant non-precious metal substrates are considered as alternatives.The Ta substrate exhibits excellent stability under acidic conditions,but its smooth surface makes it difficult to support the catalyst.Electro-oxidation is used to treat the Ta substrate to form a dense oxide layer on the surface.The porous rough surface could increase the specific surface area,but also enhance the roughness of the substrate to improve the catalyst loading capacity.Through the calcination process,the Ta₂O₅@Ta substrate with abundant oxygen vacancies is obtained.And the existence of oxygen vacancies can greatly improve the performance of catalyst electrolysis water.Nickel phosphide is further electrodeposited on this substrate,and the catalyst with the best hydrogen evolution activity can be obtained by adjusting the amount of loading.This catalyst only needs a low voltage of 20 mV and 23 mV to achieve a current density of 10 mA·cm^-2 in alkaline and acid electrolytes,and has excellent electrocatalytic water splitting performance and stability.The Ta₂O₅@Ta substrate obtained by this preparation strategy has the potential to become a new type of non-noble metal-based substrate.It exhibits excellent stability under alkaline and acidic conditions and can be used as an effective substrate for other active materials for other electrocatalytic reactions.