The Preparation Of Cobalt-based (Hydroxide) Oxides Electrocatalysts And The Properties Toward Oxygen Evolution Reaction

As a promising green energy carrier,hydrogen（H₂）can reduce our dependence on fossil fuels（such as oil and coal）and alleviate the environmental problems.Water electrolysis is an efficient and clean technology for producing hydrogen,however,the the hydrogen production efficiency is currently bottlenecked by the sluggish kinetics of oxygen evolution reaction（OER）,which needs to overcome the high reaction barrier.Therefore,researchers design a variety of efficient catalysts to accelerate OER process,among which cobalt-based catalysts are considered as one of the ideal electrocatalytic catalysts for OER due to their low cost,abundant and good theoretical OER activity.However,it is still suffering from poor performance and stability that hindering its further improvement and practical application.In our research,we regard cobalt-based（hydroxide）oxide catalysis as research object,and understand thoroughly the total composition of potential in OER process.Based on the optimization of OER performances can be realized through enlarging the surface area of the catalyst（increase the number of active sites）or tuning the intrinsic electronic structure of active sites（enhance the activity）,we studied the effect of composition and morphology structure to the OER properties of catalysts deeply,which can provide reference for the practical application of water electrolysis.The main research contents are as follows:First,The hollow cobalt-nickel oxide microspheres（h-CNMs）assembled with 2D ultrathin porous nano-sheets with adjustable Co/Ni molar ratio were successfully synthesized by"self-template"method.The results indicate that the best OER activity is achieved when Co/Ni molar ratio reaches 2:1 for h-CNMs.This catalyst shows a small overpotential of³10 mV at 10 mA cm^-2,the Tafel slope value of Co₂-Ni₁-O is 57 mV dec^-1.Impressively,at high overpotential,the OER current density of Co₂-Ni₁-O even surpasses that of benchmark IrO₂ catalyst.Further studies the impact of the composition and morphology structure on OER performance show that the excelent activity of catalysts can be attributed to the large electrochemically reactive surface（increase the number of active sites）and the good charge conduction offered by the synergetic effects between its unique structural features and the tunable Co/Ni compositions.Second,except cobalt oxides,a series of hierarchical porous Co_x-Fe_y LDH samples composed of 2D ultrathin nanosheets for OER were synthesized by simple one-step wet chemical method.Studies show that the molar ratio of Co/Fe has an important impact on the morphology and OER performance of catalysts.When current density j₀=10 mA cm^-2,the required overpotential is 262 mV and Tafel slope is 41.9 mV dec^-1,which is significantly better than Co₂-Ni₁-O.The experimental results once again confirm that the importance of the synergistic effect between composition and structural features in improving OER performance.Third,a series of ternary CoFeCr LDHs nanomaterials were obtained by hydrolysis of ternary CoFeCr metal alkoxide percursors under alkaline conditions.Based on doping effect,the main laminate of Co-Fe LDH was modified by introducing Cr³⁺.The experimental results show that the introduction of Cr³⁺can regulate the electronic structure of the main laminates,enhance the catalytic activity of active sites,and improve the electronic transmission capacity of LDH materials during OER process,thus improving their OER performance.Furthermore,the CoFeCr LDH can achieve a catalytic current density of 10 mA cm^-22 at an overpotential as low as 230 mV and a small Tafel slope of 38mV dec^-1,which is significantly more active than Co-Fe LDH.