Copper Oxide And Iron-Nickel Phosphide Nanosheets For Electrocatalytic Water Oxidation

Water splitting into hydrogen and oxygen can store energy into chemical fuels,which has been extensively considered as a crucial step to address the rapid growth of energy consumption and the associated environmental issues.When coupled with solar-to-electric power conversion,water splitting via an electrolyzer can enable the direct use of intermittent solar energy at no environmental cost.As the key half-reaction,the oxygen evolution reaction(OER)has a high activation barrier that is coupled with the transfer of four electrons and four protons,presenting a bottleneck in the transformation of water into O2 and H2.In last few decades,ruthenium dioxide(RuO2)and iridium dioxide(IrO2)have been widely studied and are currently considered as the most efficient OER catalysts due to their low Tafel slopes and overpotentials,particularly in basic solutions.However,their large-scale applications are limited by their scarcity,ultrahigh cost,and instable catalytic performance.Therefore,great efforts have been devoted to the discovery of highly efficient and stable OER catalysts,especially to replace precious metals by cost-efficient transition-metal-based catalysts.However,transition metal catalysts usually have poor conductivity,which greatly limits their catalytic efficiencies.Therefore,on the basis of previous work,we directly grew the catalysts on a conductive substrate as an electrode,which eliminates the use of a binder and greatly improves the charge transfer in the catalytic process.This article mainly includes two parts of CuO nanosheets and FeNiP solid solution nanosheet arrays:1.CuO nanosheets grown in-situ on copper foam substrate for electrocatalytic water oxidation.An active catalyst directly composed of CuO nanosheets has been synthesized on the 3D framework copper foam,demonstrating large specific surface area,more catalytic active sites and fast charge transport kinetics.Among the all tested samples,the CuO nanosheets prepared by a simple hydrothermal at 120? for 45 min exhibit excellent electrochemical performance towards OER with a low onset potential(?1.58 V vs.RHE)and high catalytic current density.In addition,the CuO nanosheets also exhibit strong durability in 1 M KOH solution.The slope of the Tafel plot is 60.9 mV/dec.The enhanced catalytic activity can be ascribed to 3D nanosheet structure,high electroactive surface area and strong chemical coupling between CuO and copper foam substrate.The CuO samples were also characterized by X-ray powder diffraction(XRD),scanning electron microscopy(SEM)and X-ray photoelectron spectroscopy(XPS).2.Electrocatalytic water oxidation activity of FeNiP solid solution nanosheets grown on nickel foam substrate.We report the synthesis of novel FeNiP solid solution nanoplate(FeNiP-NP)arrays and their use as an active catalyst for high-performance water oxidation catalysis.The as-prepared FeNiP-NP catalyst on 3D nickel foam substrate exhibits excellent electrochemical performance with a very low overpotential of only 180 mV to reach a current density of 10 mA cm-2 and an onset overpotential of 120 mV in 1.0 M KOH for the oxygen evolution reaction.The slope of the Tafel plot is as low as 76.0 mV dec-1.Furthermore,the long-term electrochemical stability of the FeNiP-NP electrode was investigated by cyclic voltammetry at 1.10-1.55 V vs.RHE,demonstrating very stable performance with negligible loss in activity after 1000 CV cycles.To the best of our knowledge,this present FeNiP-NP solid solution represents the best OER catalytic activity among the non-noble metal catalysts reported so far.