Preparation Of Self-supporting Transition Metal Nanoarray Electrodes And Its Performance For Electrocatalytic Water Splitting

Hydrogen fuel is the cleanest fuel due to its high energy density and only yield of water as it burns.Among the many hydrogen production methods,electrocatalytic water splitting is one of the most ideal and cleanest way.Currently,the electrocatalysts with excellent hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）activities are Pt and Ru O₂/Ir O₂,respectively.However,because of the scarcity of precious metal reserves,high price and poor stability,their large-scale applications are greatly limited.Therefore,it is urgent to develop non-precious metal electrocatalysts with high activity,low price and robust stability toward HER and OER.Self-supporting transition metal catalysts on conductive substrates can be directly used as working electrodes without binders.The binder-free self-supporting electrodes can not only accelerate the charge transfer kinetics,but also prevent the catalysts from detaching from the current collector during the generation of bubbles,thereby improving the catalytic performance and stability of the catalysts.In view of the points mentioned above,we designed and synthesized a series of self-supporting transition metal-based catalysts for electrocatalytic water splitting from the perspectives of modulating morphology,atomic doping,constructing heterostructures and metal alloy.The main research contents of this thesis are summarized as follows:1.Ni/Ni₂Mo₃O₈ nanoarray catalysts（Ni/Ni₂Mo₃O₈/CC）were directly grown on carbon cloth（CC）through the weak alkali etching strategy,followed by a high temperature calcination process.The experimental results demonstrated that heterojunctions were at the interface between metallic Ni nanoparticles and Ni₂Mo₃O₈ nanowires.Furthermore,the surface electronic structures of Ni and Ni₂Mo₃O₈ were rearranged near the Ni/Ni₂Mo₃O₈ heterojunction,thus improving the electrocatalysis of Ni/Ni₂Mo₃O₈/CC performance.When Ni/Ni₂Mo₃O₈/CC was used as the anode and cathode for overall water splitting,the self-supported electrodes only needed a voltage of 1.51 V to achieve 10 m A cm^-2 in 1.0 M KOH electrolyte.The experimental results showed that the unique structure of the self-supporting array and the electronic interaction at the heterojunctions can effectively improve its catalytic performance.2.A dicyandiamide-assisted high-temperature treatment method facile strategy was used to prepare Ni/Mo C nanoparticles embedded within nitrogen-doped carbon nanotube array catalysts（Ni-Mo C@NCNT/CC）on CC.The as-prepared Ni-Mo C@NCNT/CC had excellent catalytic activities,requiring only 70 and 219 m V overpotential at 10 m A cm^-2 for HER and OER,respectively.At the same time,Ni-Mo C@NCNT/CC had excellent catalytic performance for overall water splitting.The excellent catalytic activity of Ni-Mo C@NCNT/CC was attributed to the synergistic effect between Ni and Mo C nanoparticles and the unique three-dimensional structure of the self-supporting electrode.3.Using the conductive bimetallic organic framework on CC as the precursors,the Cu Co and Cu Ni alloy nanoparticles embedded within nitrogen-doped carbon nanotube array catalysts（Cu Co@NCNT/CC and Cu Ni@NCNT/CC）were prepared via a one-step calcination method.The effects of Cu/Co and Cu/Ni ratios on the catalytic performance were investigated.The experimental resutls showed that the optimized Cu Co@NCNT/CC and Cu Ni@NCNT/CC had excellent overall water splitting performances,which were attributed to the higher catalytically active areas of the Cu Co and Cu Ni alloys.In the meanwhile,in 1 M KOH+0.5 M Na Cl electrolyte,the catalytic performances of Cu Co@NCNT/CC and Cu Ni@NCNT/CC still had stable activity toward overall water splitting,indicating their potential applications in the seawater electrolysis.