Study On The Stability Of Nickel Oxide Anodes For Electrocatalytic Conversion Of 5-hydroxymethylfurfural To 2,5-furandicarboxylic Acid

Biomass energy has a plentiful and renewable resource with huge potential for reducing human dependence on petroleum-derived chemicals.As an important platform compound derived from cellulose,5-hydroxymethylfurfural（HMF）has a variety of functional groups,which enables the synthesis of a wide range of chemicals by thermocatalytic,enzyme-catalyzed,photocatalytic,and electrocatalytic means.The electrocatalytic conversion method offers notable advantages such as mild reaction conditions,environmental compatibility,and strong reaction manipulation.Efficient electrochemical conversion of HMF can significantly alleviate the environmental and resource burden.In the conversion of HMF,2,5-furandicarboxylic acid（FDCA）is spotlighted,which can be used as a precursor to prepare polymers,and these biomass-derived polymers are superior to conventional polyethylene terephthalate in terms of oxygen barrier and reproductive toxicity.Presently,research on the electrocatalytic oxidation of HMF to produce FDCA has increased annually.However,most studies focus on enhancing the selectivity and current efficiency,while rarely concerning the issues of electrode stability.Nevertheless,electrode stability is the most important indicator of its ability to be applied.Consequently,this study explores the electrode stability during the electrocatalytic conversion of HMF,focusing on the following aspects:（1）Crystalline and amorphous nickel hydroxide-modified nickel foam electrodes were selectively prepared to investigate the influence of the crystalline phase on the activity and stability of the electrocatalytic oxidation of HMF to produce FDCA.The preparedβ-Ni NS/NF electrodes had a strong adsorption capacity for HMF,leading to better intrinsic electrocatalytic activity.On account of stronger crystalline matching degrees,the crystalline electrodes facilitated electron transfer at the catalyst/substrate interface and enhanced interfacial stability.Remarkably,the electrode achieved an FDCA yield of 80.6%at a current density of 30 m A/cm².（2）The classical nickel oxide electrode supported by nickel foam was used as a research object to analyze the failure mechanism during the HMF oxidation process.Through the utilization of electrochemical in situ Raman spectroscopy and high-resolution transmission electron microscopy,it was observed that the surface catalytic layer of nickel oxide（Ni O_x）on the nickel foam experienced a phase transition and exfoliation phenomenon under constant-current electrolysis conditions.In an alkaline solution,the catalytic layer transitioned from Ni（OH）₂ toβ-Ni（OH）₂and further toβ-Ni OOH.With the electrolysis proceeding,concentration polarization hindered the timely arrival of reactants at the electrode surface,resulting in potential increase and the occurrence of oxygen precipitation side reactions.Consequently,the catalytic layer was changed toγ-Ni OOH.The ICP-OES results confirmed that the substrate dissolution occurred,with the exfoliation of the catalytic layer exacerbating this phenomenon.Additionally,as the reaction continuously proceeded,the oxygen precipitation side reaction was intensified,and the detachment of gas from the electrode surface accelerated the detachment of the catalytic layer.The phase transition and exfoliation of the catalytic layer,the dissolution of the substrate,and the oxygen precipitation side reaction synergistically led to the failure of the electrode.Based on these,a strategy is proposed to enhance the stability of self-supported nickel oxide electrodes for electrooxidation synthesis.（3）Based on the understanding of the failure mechanism of nickel electrodes,we successfully prepared a highly stable nickel-containing binary composite oxide electrode（Ni O-Cu O/Sn Sb O_X/Ti）with potential applications.The electrode utilizes titanium as the matrix material for its higher electrochemical stability,effectively addressing the issue of nickel matrix dissolution.We incorporated an electrochemically activated Sn Sb O_X intermediate layer to enhance the bonding between the surface-active phase and the matrix,thereby inhibiting the detachment of the catalytic layer.Furthermore,the inclusion of Cu O in the catalytic layer introduced an internal built-in electric field,resulting in an elevated electron transfer rate.The addition of Cu also generated an abundance of oxygen vacancies,promoting the interfacial electron transfer rate between the catalytic layer and the intermediate layer.Moreover,the adsorption of OH^-by Cu O inhibits the phase transition of the catalytic layer and the shedding of the catalytic layer caused by OH^-enrichment around Ni（OH）₂.The above purposeful overall design of the electrode improves its intrinsic electrocatalytic activity for oxidizing HMF and the stability of the electrolysis system,which in turn suppresses the oxygen precipitation side reaction.The electrode successfully demonstrated long-term electrolysis performance under both constant-current and constant-potential conditions,exhibiting excellent stability.