Paired Electrochemical Conversion Of Furfural:From Reaction Design,Electrode Preparation To System Construction

Facing the increasing environmental and resource challenges,the direct production of high value-added chemicals and fuels from biomass can reduce the dependence on petroleum resources.The utilization of abundant and cost-effective biomass resources is also the backbone of green chemistry.Biomass derivative furfural(FF),as a bulk chemical,can be converted into a variety of value-added chemicals and fuels through the oxidation,hydrogenation of its aldehyde functional group(-C=O)and ring-opening reactions through electrochemical methods.During the electrochemical conversion of furfural,paired electrolysis can significantly improve the current efficiency,which can theoretically reach 200%.Although the typical paired electrochemical conversion of furfural,which simultaneously converts to furfuryl alcohol and furoic acid has been achieved,there are still problems such as single electrolysis system,fixed reaction products,and poor compatibility of cathodic and anodic reactions.As a key universal platform chemical,designing new paired electrochemical conversion systems for furfural to expand product distribution is of great significance and industrialization prospects.This thesis aims to construct novel paired electrolysis systems of furfural,focusing on the design of cathode and anode half-reactions and the preparation of electrode materials,exploring the direct/indirect electrochemical conversion mechanism and the interaction between catalytic electrode/mediator and the target substance during electrolysis,to achieve the highly matched paired electrochemical conversion of furfural.The main research results are as follows:(1)By designing the coupling of hydrogen peroxide-mediated furfural cathodic conversion which was produced by oxygen reduction and iodide ion-mediated furfural anodic oxidation,a linear paired electrolysis system was successfully constructed to realize the synthesis of furoic acid in both sides of the separated flow electrochemical reactor simultaneously.The electron transfer paths of the cathodic and anodic reactions were elucidated.The anode introduced iodide ions as the redox mediator,which transformed the traditional direct electrocatalytic conversion into an "electrochemicalchemical" indirect catalytic conversion,reduced the sensitivity to potential,and provided a matching space for the cathodic and anodic reactions.Foam titanium was used as the current collector,and oxidized carbon nanotubes(O-CNTs)were used as catalysts to prepare the gas diffusion cathode.Hydrogen peroxide generated by twoelectron oxygen reduction on O-CNTs gas diffusion electrode was used to mediate the cathodic conversion in situ.The same electrolyte environment of anode and cathode made the reaction compatibility good,the electron efficiency of paired electrolysis reached 125% and reduced energy consumption by about 22%.Through the construction of the linear paired electrolysis system,both the matching problem of the catalytic currents of cathodic and anodic reactions(by introduction of the indirect electrolysis method)and the problem of reaction compatibility were solved.(2)In view of the serious loss of graphite anode and low oxygen evolution overpotential at high current density,the mesh lead dioxide electrode was further used as the anode,and the catalyst amount of 2,2,6,6-tetramethyl-1-piperidinyloxy(TEMPO)was used as the redox mediator.The mesh electrode was designed to reduce the resistance of electrolyte flow and increase the contact area between the mediator and the electrode,so that the reaction can be carried out more fully.The efficient conversion of furfural to furoic acid in anolyte was realized and the reaction mechanism of the indirect oxidation process was further elucidated.The prepared lead-loaded rice huskbased hierarchical porous carbon(Pb/RHPC)gas diffusion cathode with high porosity and high hydrophobicity formed a characteristic gas-solid-liquid three-phase interface composed of gas,catalyst and electrolyte during the electrolysis process,which significantly improved the catalytic efficiency of two-electron oxygen reduction.At the same time,the introduction of lead could effectively inhibit the hydrogen evolution reaction of carbon-based materials.Furfural cathodic conversion was achieved by hydrogen peroxide-mediated process.Compared with the previous work,this system not only improved the stability of the anode,but also avoided the influence of hydrogen evolution and oxygen evolution side reactions on electron efficiency and yield.The high-efficiency conversion of furfural at large current density was realized,which broadened the application prospect of this system in industrial electrolysis.(3)Investigating the product distribution of the electrocatalytic oxidation and electrocatalytic hydrogenation of furfural in acidic electrolyte.Taking maleic acid and2-methylfuran as target products,a divergent paired electrochemical conversion system of furfural was successfully constructed.The lead dioxide plate was selected as the anode,which solved the problems of poor electrode stability and severe oxygen evolution side reactions under high oxidation potential in acidic environment.The efficient electrocatalytic oxidation of furfural to maleic acid was achieved,and the product transformation rules during the oxidation were elucidated.Cu Sn/Cu F@Cu cathode electrocatalyst was fabricated by secondary co-deposition of copper and tin using electrodeposited copper foam as the substrate.The hydrogen evolution of Cu was solved by introducing Sn to improve the selectivity and Faradaic efficiency of 2-methylfuran.The performance of the electrocatalysts and the pathways of electrocatalytic hydrogenation of furfural to 2-methylfuran were investigated by combining experiments with the density functional theory(DFT)calculation.In divergent paired electrolysis system,the electrons generated by the anodic electrocatalytic oxidation of furfural were used for valuable and controllable cathode electrocatalytic hydrogenation,which not only greatly reduced the cost of electricity,but also further expanded the product distribution of furfural paired electrochemical conversion.