Preparation And Performance Of Self-supported Tungsten Oxide-based Electrocatalysis For Water Splitting

With the development of global modern technology,the excessive use of nonrenewable energy such as oil and coal has caused serious environmental pollution and energy shortage.In order to alleviate energy pressure and address environmental problems,it is of great urgent to explore clean and sustainable energy resource.Hydrogen is expected to play a significant role in the development of sustainable energy due to its clean,high-energy density and renewable energy.Water splitting known as a clean and scalable hydrogen evolution technique,has attracted extensive attention in recent years.Here,morphology control,defect regulation and interface construction are used to modify tungsten oxide.We systematically explored the effects of acid concentration,etchant dosage,heat treatment temperature and interface electronic structure on the performance of water electrolysis.And we synoptically reveal the relationship among the superior water electrolysis performance of tungsten oxide with morphology,defect and interface modification.The main research content are as follows:(1)Ni-WOx nanoparticles were prepared on the surface of nickel foam by hydrothermal method and heat treatment for hydrogen evolution reaction.Hydrochloric acid(HCl)is used to regulate the pH of the reaction environment.In an acidic environment,nickel foam can react with hydrogen ions and release nickel ions to provide Ni source for the reaction.Therefore,nickel foam not only can be used as a current collector,but also as a nickel source to participate in the reaction.The experimental results show that the size of Ni-WOx nanoparticles decreases with the increase of HCl dosage.When the content of HCl is too high,Ni-WOx nanoparticles will agglomerate and their crystal phase will also change.When the amount of HCl is 300 μL,Ni-WOx has the smallest contact resistance and faster charge transfer rate,and exhibits excellent HER performance in alkaline media(at 20 mA cm-2,the overpotential is 96 mV,and the durability exceeds 10 h).(2)A self-supporting serrated Ni-WO3 electrode was prepared by a simple insitu etching method using(NH4)2SO4 as the etchant for oxygen evolution reaction.By studying the effect of etchant types on the structure of Ni-WO3,it is found that NH4+ and SO42-play an indispensable role in the unique structure of Ni-WO3.As a result,Ni-WO3 without etchant exhibits an octahedral structure with an overpotential of 365 mV at a current density of 10 mA cm-2.The overpotential of the serrated Ni-WO3-3(where 3 is the mass of(NH4)2SO4,unit:g)electrode at 10 mA cm-2 is only 265 mV.Interestingly,the structure and composition of the serrated Ni-WO3 electrode undergo a self-reconstruction process during the oxygen evolution process,and the final catalyst is connected by low-crystallinity nickel hydroxide nanoparticles.(3)Ni-WOx catalyst with abundant oxygen vacancies was fabricated on nickel foam by hydrothermal method and hydrogen treatment reduction method for hydrogen evolution reaction,and deeply investigate the effect of calcination temperature on catalytic performance.Experiments demonstrate that with the increase of calcination temperature,Ni-WOx structure evolves from stacked nanosheet structure to nanowire structure.When the calcination reaches 550℃,the obtained Ni-WOx nanowires structure possess the most abundant oxygen vacancies and exhibit excellent hydrogen evolution activity.In 1 M KOH electrolyte,it only needs an overpotential of 86 mV to achieve a current density of 10 mA cm-2,and has a low Tafel slope(71.8 mV dec-1).This excellent performance can be attributed to the following factors:1)in-situ growth of nanowire structure;2)The synergistic effect of Ni and WOx;3)abundant oxygen vacancies.(4)The iron ion chelating tannic acid layer was coated on the Ni-WOx nanowires via an interfacial coordination assembly method to synthesize TA-Fe@Ni-WOx hierarchical structure composite for oxygen evolution reaction.The TA-Fe@Ni-WOx has rich active sites and good electrical conductivity.XPS and UPS results show that the electronic structure of Ni-WOx is optimized after the introduction of TA-Fe nanosheets.The Fermi level of TA-Fe@Ni-WOx moves upward,and has a smaller ionization potential and a richer electronic environment.Therefore,TA-Fe@Ni-WOx is more conducive to the oxygen evolution reaction.In alkaline electrolyte,the overpotentials of TA-Fe@Ni-WOx at current densities of 20 and 50 mA cm-2 are 240 and 260 mV,respectively,and the cycle stability exceeds 10 h.