Synthesis And Electrocatalytic Performance Of Self-supported Bi-metallic Catalysts On Ni Foam

Hydrogen has many merits such as high heating value,no pollution,wide sources and high environmental compatibility,which has been expected to replace traditional energy and realize the environmental protection and the sustainable development of economy and society.One of the most important research topics is how to realize the clean preparation of hydrogen.Hydrogen production by electrocatalytic water splitting is an ideal way to achieve above goals.Overall water splitting（OWS）includes two half-reactions:hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.However,the thermodynamics of them are relatively slow.In theory,a voltage of at least 1.23 V is required for the reaction to occur.Meanwhile,due to the slow reaction kinetics,an additional overpotential needs to be applied during actual electrolysis,which greatly increases the consumption of electricity.An important way to solve these problems is to reasonably design catalysts with high activity.Noble metal（such as Pt,Ru,Ir,Pd）-based catalysts are highly active but expensive for electrocatalytic OWS.Recently,there are more and more researches on transition metal-based catalysts,some catalysts even have comparable catalytic activity to noble metals,making it possible to realize low-cost and high-efficiency water splitting.The structural design of catalysts is one of the important ways to achieve high activity,and the electrocatalysts grown directly on the conductive substrate can avoid the reduction of active area and conductivity as well as the coverage of the active sites caused by directly coating with the use of polymer adhesives.Meanwhile,uniform morphology and structure can be obtained.Among them,three-dimensional metal conductive substrates such as Nickel Foam（NF）and Iron Foam（IF or FF）are commonly used.In this paper,by rationally designing the structure and composition,three new bimetal-besed materials were synthesized with foamed nickel as the substrate,which realized the high-efficiency catalysis of OWS.1.Fabrication of 2D/3D Prussian blue analogues and deritives for efficient overall water splitting.A two-step simple hydrothermal method was applied to in-situ grow two-dimensional manganese dioxide nanosheet arrays and three-dimensional MnFe Prussian blue analogue cubes in situ on NF,denoted as PBA@MnO₂.Then it is converted into NiFeMn nitride（N-Fe Mn Ni）via a one-step nitridation method.Electrochemical test results show that,thanks to the excellent two-dimensional/three-dimensional hierarchical structure,PBA@MnO₂ has abundant active sites and good charge-transfer ability,which endows it with excellent OER catalytic activity(η₁₀=238 m V in 1.0 M KOH).The nitridation product has metal-like properties,which further enhances the catalytic activity of HER(η₁₀=101 m V in 1.0 M KOH).The above materials all have good stability in 1.0 M KOH and can be further applied to OWS.Meanwhile,a series of characterization methods were used to determine the composition and morphology,revealing the inherent origin of high activity.2.Heteroatoms adjusting amorphous Fe Mn-based nanosheets via a facile electrodeposition method for full water splitting.The amorphous Fe Mn-based nanosheet array（Fe MnO_x）was fabricated in situ on the NF by a simple one-step electrodeposition method.At the same time,the heterogeneous atoms P and S（P-Fe MnO_x,S-Fe MnO_x,SP-Fe MnO_x）can be successfully incorporated by adjusting the composition of the electrolyte.Combining the characterization and electrochemical measurement results,the synergistic effect is an important reason for the high OER activity of Fe MnO_x(η₁₀=220 m V in 1.0 M KOH).Fe species have higher intrinsic activity for OER,while Mn species are beneficial to expand the active surface area.Meanwhile,the incorporation of P atoms can adjust the electronic state of Fe/Mn,and the HER activity is significantly improved(η₁₀=97 m V in 1.0 M KOH).S atom doping will adversely affect the adjustment of activity.The highlight of this work is synthesizing an efficient and cheap catalyst with a very simple method,which provides a new idea for material synthesis.3.Selective nitridation to prepare CoN/VO_x composites grown on nickel foam for efficient oxygen evolution reaction.In this work,a Co（OH）₂ and vanadium oxide（VO_x）composite material was grown in situ on nickel foam by a one-pot hydrothermal method.Then,considering the difference in temperature required for Co and V to produce nitriding products at high-temperature pyrolysis,CoN/VO_x composite material was succefully prepared.Experiments have found that the addition of V will affect the morphology of Co（OH）₂ and further affect the nitridation products subsequently.CoN will also help generating more oxygen vacancies in VO_x,which is very beneficial to the electrocatalytic process.At the same time,the above speculation was verified by a series of characterization methods.Finally,the synergistic effect of Co and V species is also manifested in the expansion of the active area,and a variety of factors jointly promote the occurrence of OER(η₁₀=228 m V in 1.0 M KOH).This work proves that the CoN/VO_x composite material is an efficient catalyst for oxygen evolution reaction,which is of reference significance for subsequent material design.