Preparation And Electrocatalytic Performance In Overall Water Splitting Of Transition Metal Oxide Nanocomposite Structure Electrocatalysts

Excessive dependence on fossil fuels makes energy increasingly scarce and environmental pollution increasingly serious.Therefore,the development of renewable and environmentally friendly energy is particularly important.Hydrogen energy is a hotspot of research and development in various countries,and electrolysis of water is considered to be an ideal way to prepare hydrogen because of its mature technology,low energy consumption,and high purity of hydrogen.However,the two half reactions of water splitting,namely oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）,have higher activation energy barriers,slow thermodynamics,and the theoretical limit voltage is 1.23 V,and the actual operation of electrolytic cell even needs 1.8～2.0V battery voltage.Some precious metal-based catalysts can effectively accelerate the reaction rate and reduce the overpotential,but their expensive price and scarce reserves have severely restricted their large-scale application in industry.It is imperative to develop cheap and easily available non-precious metal-based catalysts.However,the activity and stability of most non-noble metal-based catalysts are far from meeting the requirements.We synthesized and developed a series of transition metal oxide nanocomposite catalysts for stable and efficient electrocatalytic of water splitting from the aspects of adjusting the electronic structure,optimizing the microscopic morphology,and adjusting the element composition.The specific research content of this paper is as follows:The bimetallic oxides anchored in three-dimensional（3D）porous conductive nickel foam（NF）are constructed by a simple in-situ hydrothermal method for efficient overall water splitting.The vertically aligned Mn₃O₄/Fe₂O₃ heterojunction nanosheets have a strong interaction between hierarchical metal oxides and heterogeneous interface,which endows excellent performance toward oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）in alkaline environment.By adjusting the molar ratio of the Fe:Mn,the morphology and composition of Mn Fe O-NF-x composites（x represents the ratio of Fe:Mn）can be adjusted to exhibit diverse catalytic activities.In particular,the Mn Fe O-NF-0.4（0.4 indicates Fe:Mn ratio of 0.4:1）and the Mn Fe O-NF-0.8 display outstanding performance withη₁₀=157 m V for OER andη₁₀=64 m V for HER,respectively.Furthermore,the Mn Fe O-NF-0.4 and Mn Fe O-NF-0.8 are assembled into a water splitting electrolyzer,which can reach a current density of 10 m A cm^-2 with a low voltage of 1.59 V.Mo-doped Fe Co-（oxy）hydroxide nanosheet arrays grown directly on Fe foam（FF）are synthesized via a cost-effective and energy-efficient corrosion engineering method,which is realized via the controlled oxygen corrosion reaction of FF.Furthermore,high-valence Mo doping can efficiently regulate the electronic coordination environment,and the control of the corrosion time can fabricate amorphous-crystalline heterostructures.Therefore,the as-prepared catalyst exhibits advantageous catalytic performance for OER(η₁₀₀=212 m V).This work shows that the corrosion engineering method and incorporation of high-valence metal modulators are advantageous directions for the development of high-activity and cost-effective electrocatalysts.Interestingly,this method has universality and is easy to be extended to other metal oxide composites.Co-Mn bimetallic oxide nanosheet arrays were directly grown on nickel foam by hydrothermal method using potassium permanganate,cobalt salt and PVP as raw materials,and then P-doped Co-Mn bimetallic oxide network structure（denoted as P-Co MnO₂/NF）was further hydrothermal synthesized.Thanks to the synergistic effect of bimetallic oxide and the electronic regulation of heteroatom P,P-Co MnO₂/NF exhibits excellent catalytic activity for alkaline HER and OER reactions,requiring overpotentials of 118 and 220 m V to achieve current density,respectively.10 m A cm^-2.Based on the excellent bifunctional catalytic activity of P-Co MnO₂/NF,when it is assembled into a two-electrode system for electrocatalytic water splitting,the battery voltage required to drive a current density of 10 m A cm^-2 is 1.58 V.