Study On Preparation And Performance Of Oxygen Evolution/Reduction Reaction Electrocatalyst

Electrocatalysis are of critical importance in the efficient implementation of the several renewable energy conversion process,which can alleviate our overexploitation of fossil fuels.However,the kinetics of the oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）energy conversion processes is extremely slow.The best electrocatalyst generally consist of rare and expensive noble metal,which greatly limits the widespread application of these electrocatalytic technologies.Low-cost amorphous nanomaterials and layered double hydroxides are highly active toward electrochemical reactions due to the structural characteristics of adjustable composition.In this paper,a solvent-controlled precipitation synthesis（SCP）method was used to successfully load ultra-thin amorphous copper hydroxide nanoclusters（A-Cu（OH）₂/GO）on a graphene substrate,showing a high selectivity of 95.4%for hydrogen peroxide produced by ORR.Combining density functional theory（DFT）calculation and in situ,ex situ X-ray absorption near edge structure（XANES）results,it is proved that the high catalytic activity originates from 3-OH-coordinated Cu sites with increased reversibility of oxidation state in amorphous structures.At the same time,it is confirmed that the SCP method is universal and can be used to synthesize GO supported the amorphous copper hydroxide with different copper content,and prepare GO supported other amorphous metal hydroxide amorphous materials A-M（OH）_X/GO（M=Co,Mn）.In addition,carbon nanotube-supported iron-cobalt-nickel-tungsten quaternary layered double hydroxide nanosheets（Fe Co Ni W-LDH/CNT）were prepared,which have good electrical conductivity and fast electron transfer rate,and show excellent OER electrocatalysis performance.1.In the application of renewable energy conversion technology,it is urgent to develop an amorphous electrocatalyst with high ORR activity.Amorphous catalysts,thanks to the abundant defect sites,incline to hold more favorable catalytic properties with higher activity and selectivity than their crystalline counterparts.While catalysis study on amorphous materials is still an incipient area of research,and the development of preparation route for various amorphous nanomaterials remains a grand challenge yet.Here,We have synthesized graphene oxide（GO）supported amorphous copper hydroxide（A-Cu（OH）₂/GO）by solvent-controlled precipitation method in the room temperature.During the electrochemical oxygen reduction process,it showed high selectivity to hydrogen peroxide（95.4%）and high-quality activity(17.4 A g^-1).Its excellent electrocatalytic performance has also been confirmed in Zinc-air battery with high yield of hydrogen peroxide(3401.5 mmol h^-1g^-1).The comprehensive investigations on A-Cu（OH）₂/GO by coupling systematic XAFS measurement with DFT caculation reveal that electrocatalytic activity and selectivity toward oxygen reduction reaction（ORR）is highly dependent on the 3-OH-coordinated Cu sites with high reversibility of oxidation state in A-Cu（OH）₂/GO.2.Based on the first work,the synthesis of amorphous samples was studied in depth.It was confirmed that the solvent-controlled precipitation method is universal.The as-plotted structure-activity volcanic curves provide an insightful and intuitive view on catalysis of the amorphous materials,signifying that A-Cu（OH）₂/GO with abundant defect sites of three oxygen coordination significantly enhance mass activity and selectivity towards H₂O₂ production.In addition,we successfully prepared other 2e^-ORR electrocatalysts,such as graphene oxide（GO）supported amorphous metal hydroxide（A-Mn（OH）_X/GO,M=Co,Mn）ORR electrocatalysts.A-Co（OH）_X/GO and A-Mn（OH）_X/GO shows higher selectivity（～74.9%and～70.6%,respectively）toward electrocatalysis of oxygen reduction conversion into H₂O₂ than their crystalline counterparts.3.Highly active electrocatalysts based on Layered Double Hydroxides（LDH）towards oxygen evolution reactions（OER）is required for the applications of renewable energy-conversion technology.The improvement of conductivity and electron-transporting capability for LDH materials remains an enormous challenge yet.Here,we synthesized carbon nanotube supported quaternary Fe Co Ni W-LDH ultrathin nanosheets with 1 nm thickness via one-pot hydrothermal methods.Under basic OER conditions,Fe Co Ni W-LDH/CNT possess superior electrochemical performance than the noble metal Ru O₂,showing a smaller Tafel slope of 41 m V decade^-1.When the current density reaches 10 m A cm^-2,the overpotential of Fe Co Ni W-LDH/CNT is as low as 258m V.Fe Co Ni W-LDH/CNT exhibit enhanced OER activity,which can be attributed to the synergistic effect of modified CNTs and doped W⁶⁺onto LDH nanosheets catalysts.The conductivity of sample can be improved by highly conductive carbon nanotubes.W⁶⁺doping in the LDH can modify the electronic structure and further enhance the electron transfer rate.