Electrocatalyst Design And Mechanism Studies Of Electrocatalytic Oxidation Of Biomass Derivatives

Biomass is a promising and sustainable source of energy and carbon for human society,and electrochemical oxidation of biomass derivatives is a clean and efficient energy conversion strategy that reduces dependence on fossil fuels.Selective oxidation of an important biomass platform molecule,5–hydroxymethylfurfural（HMF）,to prepare 2,5–furanedicarboxylic acid（FDCA）is an important option for reducing dependence on petroleum–based polyethylene terephthalate.Dehydroascorbic acid（DHA）,the oxidation product of ascorbic acid（AA）,has important roles in antioxidation,anti–aging,cell energy metabolism,and trans–blood retinal barrier transport.Electrochemical methods have been employed to prepare DHA from AA due to their high efficiency,lack of additional oxidation reagents,and compatibility with different cathodic reactions.The study of the relationship between electrocatalyst structure and performanc e is crucial in the research of electrochemical ascorbic acid oxidation（AAOR）.Although metal catalysts have been the focus of AAOR research,issues such as high overpotential,slow reaction kinetics,and ambiguous reaction mechanisms remain.This paper a ims to address these challenges by exploring the AAOR mechanism,optimizing catalyst structures,and elucidating the relationship between electrocatalyst structure and reaction activity.Furthermore,this paper aims to construct electrochemical reaction devices based on AAOR.The specific research contents are as follows:（1）Nickel based catalysts are highly effective catalysts for the electrooxidation of HMF,and the formation of the key active intermediate Ni（OH）O is the key to improving the efficiency of HMFOR reaction.In this chapter,we optimize the kinetics of Ni（OH）₂dehydrogenation through loaded Pt nanoparticles to promote the rate of Ni（OH）O formation,and Pt can significantly optimize the adsorption behavior of HMF,achieving an increase of over 8 times the catalytic activity of HMFOR.Combined with various physical characterization,it is proved that Pt improves the electron density of Ni（OH）₂through Pt–O–Ni bonds.Combining the investigation of the redox properties of catalytic materials with in situ electrochemical impedance spectroscopy,Raman spectroscopy,and ex situ photoelectron spectroscopy（XPS）analysis,it is shown that Pt could also reduce the surface dehydrogenation barrier and accelerates the formation rate of Ni（OH）O by affecting the electronic structure of Ni center.The activity analysis of the reaction group combined with theoretical calculation analysis showed that Pt significantly increased the reaction rate of the rate determining step（hydroxymethyl oxidation）,thereby enhancing the catalytic activity of HMFOR.In summary,this work provides an opportunity to improve the catalytic performance of Ni–based catalysts from a heterogeneous perspective,providing a generic strategy design for efficient HMF electrooxidation of nickel–based catalysts.（2）The strong reducibility of AA can quickly reduce Cu（OH）₂ to Cu₂O,which makes it possible to use Cu（I）/Cu（II）redox as a medium to mediate the electrochemical oxidation of AA.This chapter combines the process of electrochemical Cu ₂O oxidation to regenerate Cu（OH）₂ and the process of spontaneous reaction between Cu（OH）₂ and AA to convert the oxidation potential of AAOR into Cu（I）oxidation potential,realizing the continuous low–potential anodic oxidation reaction.The micro morpholog y changes of Cu（OH）₂ electrode during electrochemical and non–electrochemical processes were characterized by SEM and TEM.The real phase transition process of Cu（OH）₂ electrode surface in the AAOR process was studied by in situ Raman spectroscopy.The valence change of the working electrode surface was characterized and analyzed by ex situ XPS and the AAOR mechanism mediated by Cu（I）/Cu（II）redox was proposed.The room temperature electrocatalytic chemical loop（RTECL）hydrogen production system is composed of Co P as hydrogen evolution electrode and Cu（OH）₂ electrode based on indirect AAOR.Compared to traditional water electrolysis,the RTECL system requires only half of the power consumption(2.57 vs.4.83 k Wh Nm^–3 H₂).Overall,this work provides guidance for the development of hydrogen production by biomass assisted water electrolysis and organic electrooxidation systems,and provides a new reference for hydrogen production.（3）Ascorbic acid oxidation exhibits excellent conversion efficiency on the surface of carbon–based catalysts in acidic electrolytes,effectively alleviating the problems of poor stability and high cost of metal catalysts in dehydrogenation and as corbic acid base resistant systems.In this chapter,carbon paper（CP）was chosen as the substrate and a simple oxygen plasma treatment was employed to introduce oxygen–containing functional groups（OCGs）on the CP surface for the fabrication of an efficie nt AAOR electrocatalyst.Benifiting from the catalyst structure that is more favor to AAOR,the designed oxygen plasma treated carbon paper electrode（P _O–CP）can drive a current density of 100 m A cm^–2 at 0.65 V_RHE,significantly superior to the original carbon paper（CP）and other metal based electrocatalysts.The Faraday efficiency of over 90%towards DHA production has also been achieved at the P _O–CP electrode,with long–term stability.Based on the data of electrode structure changes and reaction kinetic s changes,theoretical calculations were used to explore the relationship between OCGs with well–defined structures and the Gibbs free energy change（?G）of the AAOR elementary step,indicating that OCGs improve the efficiency of the entire reaction by reducing the dehydrogenation barrier of AA.Furthermore,the OCGs–modified CP catalyst was integrated into a proton exchange membrane electrolyzer to evaluate the efficiency of hydrogen production.Each cubic meter of hydrogen generated by the system requires only 1.54 k Wh of electrical energy,which is almost one–third of the traditional electrolytic water（4.95 k Wh）.The results suggest that the OCGs–modified CP catalyst offers a promising strategy for low energy consumption and environmentally friendly electrochemical biomass upgrading and hydrogen production,and provides a reference for electrode design adapting to large–scale production.（4）The catalytic mechanism of ascorbic acid oxidation on the surface of carbon materials in acidic media is currently lacking in in–depth research,which hinders the development of high–efficiency catalysts.In this chapter,the proton–coupled electron transfer（PCET）mechanism of AAOR on carbon materials is investigated using electrochemical tests and kinetic isotope eff ects,with a focus on optimizing the PCET reaction kinetics by using proton media.A liquid–phase phosphorylation strategy is employed to modify the surface of commercial carbon powder（XC 72）with phosphate,and the surface composition of phosphate–modified XC 72（PM–XC 72）is characterized by X–ray photoelectron spectroscopy（XPS）,Fourier transform infrared spectroscopy（FT–IR）,and temperature–programmed desorption of ammonia（NH₃–TPD）.A series of electrochemical tests are carried out to analyze the re action kinetics of AAOR on the carbon surface,and the effect of phosphate on the catalytic performance of carbon–based AAOR is investigated.The proton mediated modified XC 72 exhibits extremely high catalytic efficiency,requiring only 0.53 V _RHE to drive a current density of 10 m A cm^–2.In situ infrared spectroscopy and theoretical calculations are used to elucidate the nature of phosphate groups affecting the dehydrogenation kinetics of AAOR,indicating that phosphate groups as proton mediators regulate the reaction kinetics of the PCET process by forming interfacial hydrogen bonds.Our findings demonstrate the importance of adjusting proton transfer kinetics to promote the oxidation of ascorbic acid,and provide new insights into the rational design of c arbon–based catalysts for biomass upgrading.Overall,this work contributes to the fundamental understanding of the PCET mechanism of AAOR on carbon materials,and offers a new strategy for enhancing the catalytic performance of carbon–based electrocatalysts in biomass upgrading applications.（5）The catalytic activity of ascorbic acid oxidation on the surface of carbon materials can be regulated by heteroatom doping,and the optimized electronic structure and the introduction of new active sites significan tly enhance the catalytic activity of AAOR.With carbon paper as the substrate and electrodeposited polyaniline as the skeleton,the precursor of heteroatom doped carbon networks is constructed through electrostatic adsorption of different anions.The N,B and N,P doped carbon networks obtained by high–temperature carbonization establish metal–free AAOR/HER electrolyzers with high performance and low cost advantages.The electronic structure and micro morphology of the electrocatalyst were analyzed by SEM,XPS,Raman.The three–dimensional skeleton and uniformly distributed heteroatoms provided sufficient and efficient active sites for the reaction.The el ectrochemical test results show that N,B doped carbon nanonetworks exhibit efficient catalytic activity,and a cur rent density of 10 m A cm^–2 can be obtained with a potential of 0.443 V_RHE(0.494 V_RHE@100 m A cm^–2).A series of electrochemical tests were us ed to explore the influence of heteroatoms on the AAOR performance of carbon materials,and the reactive sites were analyzed by controlling the bonding of heteroatoms,indicating that the N–C_x–B configuration structure was the main active site.Finally,th e AAOR and HER catalyzed by N,B and N,P doped carbon networks were integrated into the proton exchange membrane electrolyzer,and the energy consumption of the system was only 2.4 k Wh Nm^–3 H₂,which was only 50%compared to traditional water electrolysis.In this work,heteroatom doped carbon catalysts were prepared based on anionic adsorbed Polyaniline.The strategy of heteroatom co doping provides a new idea for designing efficient AAOR carbon catalysts.