Preparation And Mechanism Of Nickel-Cobalt-Based Non-Precious Metal Electrolytic Water Catalysts

Hydrogen has the advantages of high energy density and produces only water as its combustion product.There are three methods for producing hydrogen:photocatalysis,biomass reforming,and water electrolysis.Water electrolysis only requires renewable electricity to drive the reaction,and it has gained widespread attention due to its non-polluting and low-cost features.Electrolysis of water involves two half-reactions,namely,hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.Additional energy input is required to overcome the energy barrier in the reaction,so efficient catalysts are needed to accelerate the entire process.So far,precious metal-based catalysts（Ru-based,Ir-based OER catalysts,and Pt-based HER catalysts）have been the best catalysts,but their high cost and scarcity limit their commercial applications.Therefore,developing highly active,low-cost,and readily prepared catalysts is of great importance in this field.Cobalt has received focused attention from researcher due to its excellent intrinsic OER activity and superior stability.In this thesis,carbon nanotubes（CNTs）loaded with Co₃O₄ nanoparticles were first synthesized in situ on nickel foam（NF）by a one-step flame method.CNTs have good electron conductivity and highly dispersed Co₃O₄nanoparticles expose a large number of active material reaction sites,resulting in overpotentials of 288 m V@10 m A·cm^-2 and 172.9 m V@10 m A·cm^-2 for OER and HER,respectively.The OER overpotential is comparable to that of commercial Ru O₂.This method is simple,fast and suitable for large-scale applications.On the basis of the above study,Co₃O₄ doped with Ni was successfully achieved by igniting an ethanol solution of dissolved cobalt（III）acetylacetonate（Co（acac）₃）and nickel（II）acetylacetonate（Ni（acac）₂）by the flame method.30%Ni-doped Co₃O₄ could expose more electrochemical area and the charge transfer resistance became smaller,making its overpotentials of OER and HER 275.5 m V@10 m A·cm^-2 and 173 m V@10m A·cm^-2,further enhancing the performance of Co₃O₄.The Fe doping of Co₃O₄ was then achieved by flame ignition of an ethanol solution with dissolved Co（acac）₃ and iron（III）acetylacetonate（Fe（acac）₃）.Fe may replace Co³⁺at the octahedral position and activate the adjacent Co active site.The 30%Fe also plays a huge role in the structural stability of Co OOH,the real catalyst in the OER process,and these various factors reduce the overpotential of OER to 232 m V@10m A·cm^-2 with a Tafel slope of only 34.1 m V·dec^-1,resulting in a huge thermodynamic and kinetic enhancement of Co₃O₄,which further enhances its OER performance.This thesis achieved facile doping of Ni and Fe in Co₃O₄ using flame synthesis,resulting in significant enhancement of OER performance.This method provides a new approach for doping with other cations and a new strategy for doping with anions.