Structural Design Of Cobalt-based Electrocatalysts Toward Enhanced Electrocatalysis

The large-scale application of fossil fuels causes excessive CO₂ emissions and energy exhaustion.Electrocatalytic water splitting and CO₂ reduction can achieve efficient use of energy.And electrochemical methods can make the process more environmentally friendly and efficient,so it is urgent to develop efficient electrocatalysts based on earth abundant elements.Cobalt and its oxides are promising noble-metal-free electrocatalysts.In this thesis,CoNi alloy and CoMoO4 binary metal oxides are designed and optimized by means of regulating composition and dimension.The main work and results are as follows:1.Electronic modulation on catalysts is vital to improve the efficiency of electrochemical CO₂ reduction reactions?CO₂RR?.Herein,CoxNi1-x nanoalloys supported by N-doped carbon nanofibers?CoxNi1-x/N-C NFs?are constructed and regulated via facile electrospinning procedures followed by pyrolysis,to efficiently catalyze CO₂ reduction toward CO.The modulated electronic configuration is experimentally and theoretically evidenced in CoxNi1-x along with different composition and varied interactions.The d-band center up-shifts with increasing Co in Cox Ni1-x nanoalloys,leading to obvious variation in the binding energy of key intermediates?*COOH,*CO and*H,*denotes a surface active site?and the reaction free energy??G?.Among the CoxNi1-x,the Co0.75Ni0.25 features the lowest?G*COOH?positive?,and the highly negative?G*H,indicating the promoted CO₂RR but prohibited hydrogen evolution.As expected,the optimal Co0.75Ni0.25/N-C NFs afford a high CO Faradaic efficiency of 85.0%and a current density of-13.4 mA cm^-2 at-0.9 V vs.RHE in 0.5 M NaHCO3,performing among the best of noble-metal-free electrocatalysts.2.Co₃Mo/CF composite structures are constructed via heating in H2/Ar at high temperature.DFT calculation shows that the d-band center?-2.406 eV?of Mo site in Co₃Mo is close to Pt,optimizing the H adsorption Gibbs free energy.As expected,the optimal Co₃Mo/CF afforded a current density of 10 mA cm^-2 at 78 mV vs.RHE,and a Tafel slope of 33 mV dec^-1,showing excellent HER activity.3.Using the confined effect of graphene,we successfully synthesised CoMoO4/rGO for OER.The optimal 2%-CoMoO4/rGO showed the highest activity with the current density of 10 mA cm^-22 at the overpotential of only 297 mV.4.The promotion of water adsorption and water splitting by cobalt-nickel selenide/LDHs hetero-interface was studied by DFT calculation.In this part,it was found that the composite structure of CoNiSe₂/LDHs optimized the processes of water adsorption and water splitting and the free energy of adsorption were lower than those of pure CoNiSe₂ and LDHs.No further experiments are needed to verify the calculation results.In this paper,the structural design of Co-based electrocatalysts and its application in electrocatalytic reaction were studied.A series of electrocatalysts with high catalytic activity were achieved,which provided valuable methods and ideas for the development of the efficient,economical and stable catalytic design for CO₂ reduction,hydrogen and oxygen evolution.