Theoretical Study On Oxygen Evolution Reaction Mechanisms On Ni₂O And Relative Fe Doped Surface

Hydrogen is an ideal substitute for finite fossil fuels because of its high energy density and cleanliness.Electrocatalytic water splitting is one of the effective approach to producing clean hydrogen energy,including hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?,among which OER is the main reason affecting the efficiency of water splitting.Although noble metal-based OER catalysts show excellent catalytic performance for OER,the high cost and scarcity of these noble metal-based electrocatalysts severely limit their widespread applications in energy conversion systems.Therefore,the development of non-noble metal OER catalysts with high efficiency and low cost is an important research direction.In the research of non-noble metal catalysts,a correct understanding of the OER mechanism is the theoretical basis for development and application.Du to its good thermal conductivity,abundant reserves and low price,transition metal phosphates have received extensive attention in non-noble metal catalysts,but its OER mechanism has not been clarified.In this paper,the different OER paths on the surface of Ni₂P and the mechanism of OER on Fe-doped Ni₂P surface and the influence mechanism of doping were investigated via first-principles periodic.The following conclusions were obtained:Firstly,through the comparative study of different OER paths on the surface of Ni₂P,it has found that the rate-determining step is the formation process of*OOH.Due to the Gibbs free energies of*O and*OH generations in the OER process of Ni₂P are low,that has deduced the surface of Ni₂P are preferentially hydroxylated or oxidized before the rate-determining step,which is consistent with the experiments results.It has demonstrated that with the increase of*O coverage,the stability of the surface increases and the overpotential of the reaction decreases.At the same time,the conductivity and hydrophilicity of hydroxylation Ni₂P are improved,which is more advantageous in the electrolysis process.The results also have demonstrated that in non-oxygen transition metal phosphates materials,OER performance studies must consider oxygen coverage.Secondly,by studying the oxygen evolution reaction paths on the surface of Fe-doped Ni₂P,it has found that the reactive sites tend to be the three-membered ring structure of Ni,but not the three-membered ring structure with Fe doped,namely,iron did not directly participate in the OER process.The doping of iron increases the free energy of*OH and*O,which makes the d-band center downshif from E_f.It has also found the stability of the surface as increases as*O coverage.The overpotential is closely related to Fe concentration and*O coverage on the surface,when covered with low concentration of*O,Ni site preferential reacts and overpotential?decreases,and when the high concentration of*O is covered,the overpotential?increases due to the enhancement of interaction between Fe and*O,so suitable Fe doping concentration on the surface is more advantageous to OER.In conclusion,based on first-principles principle,the OER mechanism of Ni₂P and its Fe doped system has been studied theoretically,and the reaction mechanism of precursor catalysis and the influence mechanism of doping have been confirmed,which provides theoretical basis and technical guidance for the experimental design and synthesis of these compounds.Besides,this mechanism has important reference meaning for the OER reaction of the same type of non-oxygen transition metal compounds.