Theoritical And Experimental Study Of NiFe-based Layer Double Hydroxides For Oxygen Evolution Reaction

Layer Double Hydroxides(LDH)have been universally identified as good candidates for oxygen evolution reaction(OER).However,the calculation of LDH for OER have been rarely reported.In the present work,Density Functional Theory(DFT)calculations are used to evaluate the NiFe-LDH and Co-doped NiFe-LDH(001)and(1-10)facets for OER in alkaline medium.For Co-doped NiFe-LDH,two different situations are considered:Co(Ⅱ)-doped NiFe-LDH and Co(Ⅲ)-doped NiFe-LDH respectively.We consider three kinds of electrochemical catalysts(001)and(1-10)surfaces and calculate the OER overpotentials for different active sites.DFT plus U calculation results revealed that the overpotentials for Co-doped NiFe-LDHs are both lower than NiFe-LDHs,which illustrate the enhancement OER catalytic activity by doping Co.It should be pointed out that Co(Ⅲ)-doped NiFe-LDH has the lowest overpotential by η=0.413 V.The overpotential of Co(II)incorporation into NiFe-LDH was 0.481 V smaller than 0.572 V for NiFe-LDH.To further understand the effect of incorporation Co(Ⅱ)/Co(Ⅲ)into NiFe-LDH and the Co oxidation states,bader charge analysis and projected density of states(PDOS)were taken into our consideration.As a result,the valance band maximum(VBM)for Co-doped LDHs shift little to low energy with a value of 0.25 eV and have no influence on conduction band maximum(CBM).This effect perhaps accelerate the electron transfer from bulk to surface when Co expose or near the surface in slab model.Besides,bader charge analysis uncover that Co(Ⅲ)-doped NiFe-LDH have more positive charges than Co(Ⅱ)-doped NiFe-LDH.Thus,Co(Ⅲ)is more easily to accept the electrons from H20 and have advantage for OER than Co(Ⅱ).All calculations in this work are obtained from DFT plus U correction.Moreover,we have prepared Co(Ⅱ)/Co(Ⅲ)-doped NiFe-LDH by a co-precipitation method and tested their OER performance experimentally.Both incorporation Co(Ⅱ)and Co(Ⅲ)sites could improved the OER intrinsic activity of NiFe-LDH,the Co(Ⅲ)-doped NiFe-LDH catalysts can be best-performed,which showed a lower onset potential,a smaller Tafel slop than Co(Ⅱ)-doped NiFe-LDH and pristine NiFe-LDH.Thus these electrochemical results were in good agreement with our computational findings.This work should not only provide new choice for selecting high-efficient OER catalysts for water splitting,but also shed light on further optimizing the OER performance of NiFe-based catalysts.