Theoretical Study Of The Effect Of Surface Oxidation And Doped With Heterometallic Atoms On OER/ORR Properties Of Ni₂P

Two important half-reactions are involved in energy conversion/storage devices such as fuel cells and rechargeable metal-air batteries:oxygen precipitation reaction（OER）and oxygen reduction reaction（ORR）,whose slow catalytic kinetics limit their large-scale practical applications and require the development of efficient OER/ORR electrocatalysts to accelerate the reaction rate.Despite the efficient OER/ORR catalytic performance of noble metals,the high cost and low abundance limit the large-scale use of noble metal catalysts.Transition Metal Phosphides（TMPs）have promising prospects for efficient oxygen precipitation and oxygen reduction due to their abundant surface reserves,good stability,high catalytic activity and electron conductivity.The origin of Ni₂P remains controversial and lacks theoretical basis.Therefore,in this paper,the effects of surface oxidation and heterometallic doping on the catalytic performance of Ni₂P catalysts for OER/ORR under alkaline conditions were investigated using density functional theory（DFT）calculations.The main studies are as follows.（1）The effect of surface oxidation on the catalytic performance of OER/ORR on the surface of Ni₂P（001）and Ni₂P（111）was investigated.Different oxidized or hydroxylated（O*or HO*）Ni₂P（001）surface models were constructed using the Ni₂P（001）surface as a model,and the results showed that the ORR overpotential decreased significantly with the continuous loading of O atoms around the Ni₃ reaction site,and the OER overpotential had little effect.A series of oxidation surface models containing Ni₃,Ni-P and（Ni₃/Ni-P）oxidation sites were constructed based on the Ni₂P（111）surface,and the results showed that O-atom loading could modulate the surface micromorphology and electronic structure of the Ni₂P（111）catalyst,thus regulating the adsorption energy between the surface active site and the intermediate in a suitable range,and the final partially oxidized Ni₂P（111）surface exhibited excellent OER/ORR catalytic performance.Among them,the 25%（Ni₃-O/Ni-O-P）-Ni₂P（111）surface has an ultra-low OER/ORR overpotential of 0.31 V/0.24 V,which is superior to the commercial Ru O₂ catalyst OER/ORR overpotential of 0.42 V/0.37 V,respectively,and the 50%（Ni-O-P）-Ni₂P（111）surface has an 0.21 V which is significantly better than the commercial Pt/C electrode with an ORR overpotential of 0.45 V.This demonstrates that the partial oxidation of the surface is one of the key factors for the high OER/ORR catalytic activity of Ni₂P catalysts.（2）The effects of heterometallic atom doping and different loading sites of O with different O coverage on the surface OER/ORR activity of Ni₂P（111）were investigated.Fe,Co and Cu doped Ni₂P（111）surfaces were constructed separately using the Ni₂P（111）surface as a model,and the results showed that the OER/ORR overpotential magnitude of the doped surface decreased with the increase of the d-orbital electron filling number of the doped atoms.Surface oxidation and metal doping were investigated to jointly modulate the OER/ORR catalytic activity on the Ni₂P（111）surface.The results show that O loading weakens the strong interaction between Fe and Co atoms on the intermediate,while making the weak interaction between Cu and the intermediate even weaker.It indicates that O loading can modulate the adsorption energy of M-Ni₂P（111）surface with intermediates and thus further affect its catalytic activity.