Design And Preparation Of Cobalt-based Alloy/Transition Metal Oxide Composite Electrocatalysts And Investigation On Their Water Splitting Performance

Under the strategy of"emission peak and carbon neutrality",the change of the national energy structure is imperative.Hydrogen is a new type of energy,which is widely sourced,clean and low-carbon,flexible and efficient,and rich in application scenarios.It is widely considered to be an important part of the future energy structure and plays an important supporting role for Chinese green energy transition.Electrochemical water splitting is considered as a truly low-carbon and efficient hydrogen production technology due to the generation of green hydrogen.Currently,Pt-based and Ir/Ru-based compounds are used as hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）electrocatalysts for the hydrogen production of industrial electrolytic water electrolysis,respectively.However,their scarce resources and high prices make them difficult to achieve large-scale applications.Cobalt-based electrocatalysts are highly desirable alternatives to noble metals for energy applications as a result of their lower cost,natural abundance,catalytic performance comparable to that of noble metal catalysts,and good structural stability.Therefore,the development of cobalt-based catalysts is of great importance to achieve the scale up of electrochemical water splitting.Herein,a series of cobalt-based alloy/transition metal oxide composite electrocatalysts were designed and prepared by interface engineering and morphological control strategies.The morphology and composition of the samples were characterized and analyzed by means of SEM,TEM,XRD,HTREM and XPS,and the electrochemical performance of the samples was evaluated by a series of electrochemical tests,further elaborating the mechanism of the enhanced performance of the samples.The details are as follows:1.The CoMoO₄ nanosheet arrays were directly grown on nickel foam substrates with 3D open skeletons by a simple hydrothermal reaction.Subsequently,an integrated electrode comprising of Co₃Mo nanoalloys and porous CoO/Co₂Mo₃O₈ hybrid nanosheets（denoted as Co₃Mo/CoMoO_x）was developed via a facile topological transformation by directly annealing of CoMoO₄ under H₂/Ar atmosphere.This topological transformation endows the resultant Co₃Mo/CoMoO_xheterostructures with abundant and strong coupling interfaces,which could synergistically strengthen the conductivity of the catalyst and accelerate the charge transfer kinetics.Benefiting from the unique heterostructure and synergy among the different domains,the optimized Co₃Mo/CoMoO_x exhibits promising HER and OER performance with overpotentials of 26 and 256m V at 10 mA cm^-2 in 1.0 M KOH solution,respectively.Furthermore,as-assembled Co₃Mo/CoMoO_x|Co₃Mo/CoMoO_x possesses a cell voltage of 1.54 V at 10 mA cm^-2 in alkaline solution,which is preferable to many other reported bifunctional catalysts.2.A novel 3D nanostructure electrocatalyst assembled from CoRu nanoalloy and CrOOH nanosheets（denoted as CoRu-CrOOH/NF）was directly grown on nickel foam via successive hydrothermal method.The unique synergy in CoRu-CrOOH/NF heterostructures is not only conducive to strengthening charge transfer capability and accelerating the reaction kinetics but also favors the redistribution of charge within the interface,thus improving the electrocatalytic performance.In view of the abovementioned points,the resultant CoRu-CrOOH/NF displays outstanding catalytic performance with overpotentials of 26 and 272 m V at 10 mA cm^-2 for HER and 50 mA cm^-2 for OER,respectively.Remarkably,the symmetrical two-electrode cell using CoRu-CrOOH/NF only acquires 1.47 V at 10 mA cm^-2 in 1.0 M KOH,which is superior to many other state-of-the-art overall water-splitting electrocatalysts.3.The leaf-like Co-MOF nanosheet arrays template was prepared by co-precipitation method on nickel foam substrate.Subsequently,a novel heterogeneous electrocatalyst（denoted as CoMo/CoW-LDH/NF）constructed by CoMoalloy and CoW-LDH nanosheets was successfully prepared via ion etching and electrodeposition.The high-valence metal ions in CoW-LDH nanosheets are conducive to accelerating the dissociation of water,and the introduction of CoMoalloy is more favorable to promote the adsorption and binding of H*intermediates to H₂ molecules.Benefiting from the unique synergy between CoMoalloy and CoW-LDH nanosheets,as-prepared CoMo/CoW-LDH/NF heterogeneous electrocatalyst exhibits an overpotential of only 32 m V at 10mA cm^-2 in 1.0 M KOH solution.Meanwhile,the two-electrode system assembled with CoMo/CoW-LDH/NF and Ni Fe-LDH exhibits a cell voltage of only 1.52 V at 10 mA cm^-2,which is almost comparable to the assembled Pt/C||RuO₂.