Electrocatalytic Performances And Mechanism Study Of Minimal Ir-Doped Nickel-Cobalt Oxide Nanowire Arrays

The depletion of fossil fuels and the resulting environmental problems have spurred the in-depth research of new energy sources,including hydrogen.As one of the most promising alternatives to fossil fuels,hydrogen has a high energy density and environmentally friendly advantages,and has attracted widespread attentions.Hydrogen production by electrolysis of water has long been considered as one of the most attractive ways to extract hydrogen from water molecules.It includes two chemical reaction of HER?2H⁺+2e^-?H₂?and OER?2H₂O?O₂+4H⁺+4e^-?.Theoretically,in an electrochemical device,it is only necessary to apply a voltage of1.23 V between the anode and the cathode at normal temperature and pressure to completely convert water into hydrogen.However,in order to overcome the slow kinetics of the actual electrochemical reaction,the actual operating water electrolysis voltage tends to be larger than the theoretical value,and the portion above the theoretical value is usually referred to as the overpotential.The electrocatalyst can reduce the activation energy of water decomposition reactions and the corresponding overpotentials,thus improving hydrogen production efficiency of water electrolysis.Precious metal particles such as Pt and Ru are considered to be the most common high catalytically active materials,but the high cost severely limits their wide application in industry.Therefore,the development of high-activity materials based on non-precious metals is an effective way to achieve large-scale industrial hydrogen production in the future.In this paper,the one-dimensional CoxNi1-xO nanowire array is used as the structural skeleton to explore the mechanism of the influence of minimal Ir doped on the electrocatalytic performances of CoxNi1-xO nanomaterials.The main research contents are as follows:1?The Co_xNi_1-xO nanowire array doped with Ir element was successfully prepared by hydrothermal method.The doping amount of Ir was controlled below 1%.The performance of HER?OER and overall water splitting of Ir-Co_x Ni_1-xO materials were systematically studied.It was found that the minimal Ir-doping can significantly improve the electrochemical performances of CoxNi1-xO nanomaterials for water electrolysis.The Ir-doped CoxNi1-xO has the best HER and OER properties when Ir is only 0.57 wt%in the sample.For both at current density of 10 mA·cm^-2 in 1M KOH electrolyte,the Ir?0.57 wt%?-doped Cox Ni1-xO electrocatalysts exhibited very low overpotential for HER and OER of only 260 mV and 53 mV,respectively.When used as bifunctional catalysts for over all water splitting,the current density of 10 mA·cm^-2was achieved at a low applied voltage of 1.55 V.2?The density functional theory calculations?DFT?were used to analyze the Ir-doping on effect of electronic structures and the changes of Gibbs free energies of different adsorbates in Ir-Cox Ni1-xO electrocatalysts for HER and OER reactions.The calculation results indicated that the Ir-doping improved the electrical conductivity of CoxNi1-xO materials.With Ir-doping,the Gibbs free energy for adsorbed hydrogen atom on the catalysts in HER is changed from 0.823 eV to 0.523 eV,which is much more close to the value of an ideal catalyst.The Gibbs free energies for OER reaction in limiting-step were reduced by 0.33 eV after the Ir-doping,indicating that the Ir-doping also increased the catalytic activity of CoxNi1-xO electrocatalysts for oxygen production.