Construction Of Nickel-Based Catalysts For Electrocatalytic Oxidation Of 5-Hydroxymethyl Furfural

The preparation of furan-based platform chemicals from resource-rich and renewable biomass-based hexoses is of great significance for solving resource shortage and environmental degradation.As one of the furan-based platform chemicals,5-hydroxymethylfurfural（HMF）can be selectively oxidized to prepare high value-added 2,5-furandicarboxylic acid（FDCA）.The main purpose of FDCA is to replace petroleum-derived terephthalic acid for the production of biodegradable polyester raw materials.In recent years,due to the advantages of mild reaction conditions,simple operation and controllable reaction rate,the preparation of FDCA by electrocatalytic oxidation of HMF has been considered as a green and efficient biomass catalytic conversion pathway.Among many catalysts for electrocatalytic oxidation of HMF,nickel-based catalysts show great potential due to their rich three-dimensional electron number and unique e_g orbital.In this paper,the electronic structure of nickel-based catalysts was regulated by compounding with nickel foam substrate and constructing heterostructures,and the structure-activity relationship between catalyst structure and performance was systematically studied.The main contents are as follows:（1）The nitrates of nickel and cerium were converted into nickel hydroxide cerium precursors by hydrothermal method and deposited on the nickel foam substrate（NF）.The Ni O/CeO₂@NF non-noble metal catalyst with heterostructure was prepared after calcination.At room temperature,Ni O/CeO₂@NF was used as the anode,in 1.0M KOH electrolyte containing 10 m M HMF,after 30 min electrolysis（1.475 V vs RHE）,the conversion of HMF was 100.0%,the selectivity of FDCA was 99.0%,and the Faraday efficiency was as high as 99.0%.The anodic HMF oxidation was paired with cathodic hydrogen production,the rate of FDCA and hydrogen production were197.92 and 600μmol cm^-2 h^-1,respectively.After ten cycles,the catalyst still showed good catalytic activity and stability.SEM,HRTEM and XPS analysis showed that the heterogeneous interface of Ni O and CeO₂ was successfully synthesized.Ni O belongs to the face-centered cubic structure,while CeO₂ belongs to the cubic fluorite structure.The two crystal structures are different.The atomic species and arrangement at the interface are not one-to-one correspondence,so a rich interface will be generated.At the same time,Ni O is loaded on the surface of spindle-shaped CeO₂ in the form of nanoparticles,which further increases the contact between the interface and the reaction medium.This interface can also adjust the electronic properties of Ce and Ni atoms to transfer electrons from Ni atoms to Ce atoms.The optimized electronic structure of Ni O/CeO₂@NF catalyst can lead to the redistribution of charges at the interface,which is beneficial to improve the catalytic performance of HMF oxidation.（2）In the reaction system of preparing Ni O/CeO₂@NF,Co²⁺was further introduced to synthesize Ni Co₂O₄/CeO₂@NF catalyst with three-dimensional spinel heterostructure.At room temperature,using Ni Co₂O₄/CeO₂@NF as the anode,in 1.0M KOH electrolyte containing 10 m M HMF,after 22 min electrolysis（1.475 V vs RHE）,the conversion of HMF was 100.0%,the selectivity of FDCA was 97.0%,and the Faraday efficiency was 95.7%.The anodic HMF oxidation was paired with cathodic hydrogen production,the rate of FDCA and hydrogen production were265.83 and 833.33μmol cm^-2 h^-1,respectively.After ten cycles,it still showed good catalytic activity and stability.X-ray photoelectron spectroscopy（XPS）analysis showed that there was a strong interaction between Ni Co₂O₄ and CeO₂ in Ni Co₂O₄/CeO₂@NF nanocomposites.The presence of Ni Co₂O₄ was beneficial to increase the proportion of Ce³⁺related to oxygen vacancies.The presence of CeO₂increases the percentage of Ni³⁺and Co³⁺.Co³⁺and Ni³⁺can generate Ni O（OH）and Co O（OH）by absorbing OH^-in the electrolyte solution,which is beneficial to the improvement of catalytic activity.Electrochemical analysis shows that the addition of cobalt element improves the conductivity of the material,shortens the electrolysis time,and increases the rate of FDCA and hydrogen production.