Study On Catalytic Performance Of Some Ni-W Compounds As Hydrogen Electrodes In Alkaline Medium

Due to the over-exploitation and use of fossil fuels,human beings are facing serious environmental pollution and energy shortage problems.The development of clean energy is the only way to realize the important strategy of"double carbon".Hydrogen energy is considered as an ideal form of clean energy due to its high specific energy and zero greenhouse gas emissions.Electrochemical hydrolysis cells and fuel cells are the key technologies to realize hydrogen energy economy.At present,the cost of proton exchange membrane fuel cell（PEMFC）has been high for a long time in applications,and anion exchange membrane fuel cell（AEMFC）is considered as the next generation fuel cell with the most potential for commercial application.technology.At the same time,alkaline electrolytic cell technology has been well used in industrial applications due to its low cost.Hydrogen evolution reaction（HER）and hydrogen oxidation reaction（HOR）are the key half-reactions in water electrolytic cells and fuel cells,but HER and HOR are 2-3 orders of magnitude slower in alkaline media than in acidic media,which severely limits the development of alkaline electrolytic cells and fuel cells.fuel cell development.Therefore,the design and development of cheap,efficient and stable non-precious metal hydrogen electrode catalysts become the key to promote the economic development of hydrogen energy.Currently,the major non-precious metal catalysts for hydrogen electrodes are developed around Ni-based materials because of their Pt-like electronic structure and low price.However,Ni has weak adsorption ability for HER and HOR intermediates^*OH in alkaline and strong binding power for^*H,and its intrinsic catalytic activity is not high.It has been shown that the introduction of oxygenophilic elements such as W is beneficial to promote the adsorption of^*OH while balancing the adsorption of Ni on^*H,thus accelerating the reaction kinetics and improving its catalytic performance.Therefore,in this thesis we designed and developed Ni-W binary transition metal carbide catalysts（Ni₆W₆C NPs/NF）and nickel-tungsten alloy-tungsten dioxide heterojunction catalysts(Ni₁₇W₃/WO₂@rGO),and systematically investigated the structure,HER and HOR performance of the above catalysts.The main contents are summarized as follows.1.Ni_xW_yC binary carbides（Ni₆W₆C NPs/NF and Ni₂W₄C NPs/NF）were successfully synthesized by hydrothermal method and subsequent annealing treatment.The structures of the prepared materials were investigated using a series of physical characterization techniques.The prepared Ni₆W₆C NPs/NF catalyst in 0.1 M KOH at 100 mV is exhibited 2.5 mA cm^-2current density,while Ni₂W₄C NPs/NF has only 1.3 mA cm^-2 current density.Meanwhile,Ni₆W₆C NPs/NF exhibited a 42.7 mV dec^-1 Tafel slope,indicating a faster catalytic kinetic rate.In addition,Ni₆W₆C NPs/NF can maintain a current density of 1 mA cm^-2 for more than10 h at a potential of 30 mV,exhibiting a high stability.This study has scientific significance for the development of transition metal carbide-based HOR non-precious metal catalysts.2.Nickel-tungsten alloy-tungsten dioxide heterojunction catalysts were successfully prepared by wet chemical method and annealing treatment The structure of the prepared materials was investigated in detail using a series of physical characterization techniques.The prepared Ni₁₇W₃/WO₂@rGO was tested under HER at 1 M KOH with an overpotential of only24 mV at 10 mA cm^-2,and the constant current was able to stabilize for 50 h at 100 mA cm^-2.Through the LSV curve analysis of the Ni₁₇W₃/WO₂@rGO catalyst under the condition of 0.1M KOH HOR test,at a potential of 100 mV The current density can reach 2.9 mA cm^-2,and the steady-state polarization curve test at a potential of 50 mV shows a slight decay in current density after 80 h.The performance decays by only 10%relative to the starting current,showing excellent stability in long cycle use.This study has important implications for the development of high-performance heterojunction catalysts.