Controllable Preparation Of Cobalt-Based Electrocatalytic Materials And Their Electrocatalytic Performance

The vigorous development of renewable energy to produce hydrogen is one of the important ways to achieve carbon peaking and carbon neutrality goals.Electrochemical hydrogen production based on the coupling of hydrogen evolution reaction(HER)at the cathode with oxygen evolution reaction(OER)or 5hydroxymethylfurfural oxidation reaction(HMFOR),etc.at the anode will be essential ways to produce green hydrogen energy in the future.Taking the low-cost transition metal cobalt(Co)-based materials as the main research object,selfsupporting electrodes with features of high conductivity,stable structure,resistance to high current density shocks,etc.have been vigorously developed.Focusing on optimizing the geometric and electronic structures of the materials,a series of novel Co-based composites with excellent electrocatalytic HER,OER,or HMFOR performance have been developed through element doping,morphology regulation,heterointerface construction,and other regulatory means.(1)Nitrogen-doped carbon-encapsulated tungsten(W)-doped Co nanoparticle composites(CoW@N-C)are prepared as high-performance HER electrocatalysts by a hydrothermal-impregnation-pyrolysis process based on the idea of geometric and electronic structures modulation.In 1.0 M KOH,CoW@N-C only requires overpotentials as low as 55 and 100 mV to achieve current densities of 25 and 100 mA cm-2 respectively,and exhibits performance and structural stability for up to 35 h.Experimental results and theoretical calculations show that the introduced W atoms can optimize the electronic structure of Co@N-C and boost its HER activity.Guided by the material design strategy proposed in this work,CoM@N-C(M=Cr,Mo,or Ce)is also successfully prepared and exhibits significantly better HER activity than Co@N-C.(2)The introduction of an additive(EDTA·4Na)realizes the precise control of the geometric structure of the cobalt carbonate hydroxide nanoarrays supported by nickel foam(NF),and then NF/Ni2P/CoP-NS with nanosheet arrays structure and NF/Ni2P/CoP-NN with nanoneedle arrays structure are prepared by one-step phosphating.Thanks to the fact that NF/Ni2P/CoP-NS has more exposed active sites,faster electron transport,and faster mass transfer,it exhibits excellent alkaline HER activity,requiring merely 64 mV of overpotential to provide a current density of 10 mA cm-2,which is 26 mV lower than the required overpotential for NF/Ni2P/CoPNN.This work expands the morphology regulation strategy of controlling the morphology of materials by introducing additives to control ions coordination,and is expected to provide a reference for the development of other two-dimensional catalytic and energy storage materials.(3)The NF-supported cobalt-based nitride(CoNx)coupled with nitrogendoped carbon(N-C)electrocatalyst(NF/CoNx@N-C)is designed for the hydrogen evolution reaction.The introduction of N-C can not only optimize the electronic structure of CoNx to improve the intrinsic activity,but also enhance the electronic conductivity and stability of the catalyst.Thanks to the coupling between CoNx and N-C,NF/CoNx@N-C exhibits excellent HER activity(69 mV@20 mA cm-2)in 1.0 M KOH,which is significantly superior to CoNx(182 mV@20 mA cm-2).With the goal of improving the intrinsic activity,electronic conductivity,and stability of the catalyst,this work successfully carries out a "one stone,three birds" type material design,which to some extent strengthens the design principles of novel transition metal-based electrocatalysts.(4)Based on the interface engineering approach,the Co4N@CeO2 heterostructure nanosheet array is successfully constructed on NF as a multifunctional electrocatalyst for HER,OER,and HMFOR.In Co4N@CeO2,CeO2 acts as an "electron pump" to extract electrons from Co4N to optimize the interfacial electronic structure.Experimental results show that to deliver a current density of 10 mA cm-2:ⅰ)for HER and OER,Co4N@CeO2 merely requires overpotentials as low as 49 and 263 mV,respectively;ⅱ)for HMFOR,Co4N@CeO2 only needs a low potential of 1.22 VRHE(RHE stands for reversible hydrogen electrode),which is 273 mV lower than the potential required for OER.Theoretical calculations show that the introduction of CeO2 effectively lowers the potentialdetermining step barriers for both HER and OER,and facilitates the HMFOR process by optimizing the OH-adsorption.The multifunctional electrocatalyst developed in this work can realize the efficient electrochemical utilization of water and biomass,which is expected to contribute to the realization of the "dual carbon goals".