Construction Of An Efficient Self-Powered Electrocatalytic Coupling System For Hydrogen Evolution And Methanol Oxidation Based On Power Management Circuit

Hydrogen energy,with the advantages of zero pollution and high energy density,is considered an attractive alternative to carbon-based fuels.Electrocatalytic water splitting using renewable energy is a promising green hydrogen production strategy.Triboelectric nanogenerator（TENG）can effectively convert renewable energy in the environment into electric energy.The electrolytic water splitting system powered by TENG has potential application value in the field of green hydrogen preparation.However,the voltage input to the electrolytic cell is non-constant after the general power management of traditional TENG,the hydrogen generation rate is limited to a certain extent.In addition,in conventional electrolytic water splitting system,hydrogen evolution reaction（HER）occurs at the cathode while oxygen evolution reaction（OER）occurs at the anode.The slow kinetics and high theoretical potential of OER also limit the rate of hydrogen evolution.And the value of oxygen obtained by OER is low,the H₂/O₂ mixture still has explosion risk.Therefore,in order to increase the hydrogen generation rate and produce high value-added product at the anode,it is urgent to optimize the electrochemical reaction system and design suitable power management circuit.In this paper,the selective methanol oxidation reaction（MOR）was used to replace OER,the electrocatalytic hydrogen evolution and methanol oxidation coupling system with low operating voltage was constructed.On this basis,a unidirectional current rotating free-standing triboelectric-layer mode pulsed triboelectric nanogenerator（UDC RF-Pulsed-TENG）was introduced to construct an efficient self-powered electrocatalytic hydrogen evolution and methanol oxidation coupling system by designing a power management circuit.The research content of this paper mainly includes the following two parts:（1）The electrocatalytic hydrogen evolution and methanol oxidation coupling system with low operating voltage was constructed.Catalysts for selective methanol oxidation reaction were prepared by hydrothermal method.XRD,SEM,TEM,XPS and Raman characterization showed thatβ-Ni（OH）₂ was successfully grown on the surface of nickel foam（NF）.The electrocatalytic activity ofβ-Ni（OH）₂/NF catalyst for MOR was further investigated and the anodic product was analyzed.The results show thatβ-Ni（OH）₂/NF catalyst has high activity and selectivity for the selective methanol oxidation reaction.The potential at 10 m A cm^-2 was only 1.398 V（vs.RHE）,which was 290 m V lower than that in 1.0 M KOH without methanol.It can oxidize methanol to formic acid with high selectivity and Faraday efficiency approaching 100%.The morphology and crystal structure of theβ-Ni（OH）₂/NF catalyst did not change before and after the selective methanol oxidation reaction,and theβ-Ni（OH）₂/NF catalyst showed high electrochemical stability.Finally,the reaction mechanism of methanol onβ-Ni（OH）₂/NF catalyst was studied by density functional theory（DFT）,which further explained the reason why methanol was selectively converted into formic acid overβ-Ni（OH）₂/NF catalyst.The reason is that the free energy change（ΔG）of the potential determining step（PDS）*CH₃OH→*OCH₃ of formic acid formation is 0.31 e V,which is much smaller than the 0.98 e V of the potential determining step*HCOOH→*COOH of CO₂formation,so this inhibits the further oxidation of*HCOOH to*COOH,making the generation of CO₂ more difficult.Based on the study of selective methanol oxidation performance ofβ-Ni（OH）₂/NF catalyst,we successfully constructed an electrocatalytic hydrogen evolution and methanol oxidation coupling system.Compared with the conventional electrolytic water splitting system,the potential of the coupling system at 10 m A cm^-2 is reduced by 162 m V.And it can produce hydrogen at the cathode while producing the high value-added formic acid at the anode.（2）A power management circuit was designed to construct an efficient self-powered electrocatalytic hydrogen evolution and methanol oxidation coupling system.UDC RF-Pulsed-TENG was fabricated and an appropriate power management circuit was explored to manage its output energy.A power management circuit that could realize constant voltage output was designed,and an efficient self-powered electrocatalytic hydrogen evolution and methanol oxidation coupling system was constructed.The output energy of UDC RF-Pulsed TENG can achieve a constant voltage of 1.8 V applied to the electrochemical reaction cell after appropriate power management.Compared with the conventional non-constant voltage power management circuit using switch,the hydrogen production rate is increased by 1.68 times.When the rotational speed of UDC RF-Pulsed-TENG is 360 rpm,the hydrogen production rate of the electrocatalytic hydrogen evolution and methanol oxidation coupling system can reach 14.69μL min^-1,and the Faraday efficiency can reach100%.At the same time,the anode produce high value-added formic acid at a rate of 12.50μg min^-1 and the Faraday efficiency of 99.75%.This study provides a promising strategy for efficient co-production of hydrogen and value-added formic acid directly using mechanical energy,and this strategy of converting mechanical energy into high-energy density chemicals has important implications for renewable electricity storage.