Electrodeposition Preparation Of Nickel-Based Transition Metal Composite Electrode With Three-Dimensional Porous Arrays For HER Catalysis

The massive use of fossil fuels has aroused many significant concerns,including energy crisis,globe warming and severe environmental pollution,thus it is very imminent to explore renewable and clean alternative energy sources.Hydrogen is a clean and renewable energy source,which has been considered as a promising alternative to the gradually depleted fossil fuel.Hydrogen has a high energy density without emission of any greenhouse gas upon combustion.Nowadays,coal gasification and steammethane reforming are the dominated hydrogen production methods,but these processes produce a large amount of CO₂.In general,electrocatalytic hydrogen evolution reaction?HER?in alkaline media is being considered as a facile,effective and sustainable approach to produce hydrogen without any emission of carbon.There platinum?Pt?and other precious metals?e.g.,Pd,Rh?have been identified to have great electrocatalytic performance for HER.However,their high cost and low abundance extensively restrict their widespread industrialized utilization.Therefore,it is urgent to develop low-cost,noble-metal-free and high-efficiency catalysts.In this thesis,a series of noble-metal-free alkaline HER electrodes were fabricated and characterized by SEM,TEM,XRD and XPS etc.Firstly,a Ni/Ni?OH?₂ dual composition electrocatalyst was prepared via a two-step electrodeposition procedure.The stepwise technique fabricated 3D hierarchical nanoarrays as well as the concurrent electrodeposition of dual composition yielded the papillae-like hybrid crystal structure.The high electrochemical active surface area,defect-rich hybrid crystal structure,and synergistic effect of dual composition provided the elevated catalytic performance.Only 53 mV overpotential was needed to deliver the current density of 10 mA cm^-2 with small Tafel slope of 54.5 mV dec^-1 to catalyze HER in alkaline media.81%catalytic activity could be maintained after 20 h continuous test,demonstrating long-termstability.Sencondly,a novel alkaline HER catalyst,namely Ni/Ni?OH?₂ decotated NiCo₂O₄nanorod arrays on Ni foam,was fabricated via three-step process,including hydrothermal method,annealing and electrodeposition.As an electrode for hydrogen evolution reaction in alkaline media,the optimized Ni/Ni?OH?₂-Ni Co₂O₄/NF exhibited superior catalytic activity in 1 M KOH.Only 60 mV overpotential was required to deliver the current density of 10 mA cm^-2 with small Tafel slope of 67.2 mV dec^-1.The optimized Ni/Ni?OH?₂-Ni Co₂O₄/NF also presented long-termelectrochemical stability,fromwhich the catalytic activity can be maintained for at least 23.5 h.The superior HER efficiency is mainly attributed to the synergetic effect of Ni and Ni?OH?₂ and the large surface area of the electrode.Finally,the Ni/Ni?OH?₂-CoMoO₄/NF electrode was prepared by the combination of hydrothermal method,annealing and electrodeposition.Under the optimumelectrodeposition time?1500 s?,the Ni/Ni?OH?₂-CoMoO₄/NF-1500 showed outstanding HER activity in 1 MKOH.Its Tafel slope was 93.2 mV dec^-1 and only 86 mV overpotential was needed to reach the current density of 10 mA cm^-2.It also exhibited strong long-termelectrochemical durability,approximately 81.3%catalytic activity could be maintained after 22 h continuous test.This thesis reported three effeicient non-noble alkaline HER catalytic electrodes and suggested a valuable methodology in the synthesis of electrocatalysts.