image: The scheme and EXAFS patterns of atom structure characterization for NiO-Co3O4 electrode, and the in-situ SFG patterns of reaction pathways characterization of HMF oxidation to FDCA.
2,5-furandicarboxylic acid (FDCA), which is produced by oxidation of 5-hydroxymethylfurfural (HMF), is the crucial precursor for the production of polyethylene 2,5-furandicarboxylate to replace petroleum-derived polyethylene terephthalate. Electrochemical oxidation of HMF to FDCA is regarded as a clean and environment-friendly process since electrons drive the reaction at the cathode without extra chemical oxidants. Since abundant 3d electrons and unique eg orbitals enhance the covalency of transition metal-oxygen bonds, Ni-based catalysts have been considered as a great candidate for HMF electrocatalysis. For instance, a porous Ni-based electrocatalyst was prepared by the electrodeposition method for alcohol and hydrogen evolution reactions. Ni2P nanoparticles and porous Ni3S2 were reported as efficient electrocatalysts for HMF oxidation.
Very recently, Dr. Yuqin Zou and colleagues in Hunan University elaborately prepared a hierarchically nanostructured NiO-Co3O4 electrode with plentiful interface defects through a simple hydrothermal-annealing method. The interface effect could create rich cation vacancies, modulate the electronic properties of Co and Ni atoms, and raise the oxidation state of Ni species. As a result, the as-synthesized hierarchical NiO-Co3O4 nanosheets exhibited the excellent HMF oxidation activity and stability. Furthermore, in-situ SFG results and ex-situ HPLC were used to better understand the reactive intermediates and pathways during the HMF oxidation. The current study offers an efficient way to create cation vacancies at the interfacial sites and proves the positive role of cation vacancies on catalyzing the HMF electro-oxidation. The current study offers an efficient way to create cation vacancies and proves the positive role of cation vacancies on catalyzing the HMF electro-oxidation.
Recently, this research group also demonstrated the catalytic activity of Ni3N for HMF oxidation. Besides, NiO electrocatalysts are impressive in biomass conversion due to their low cost and simple synthetic methods. On the other hand, the interface engineering is a promising approach to modulate the electronic properties, tune the intermediate adsorption, and expose more active sites. For example, the core/shell NiO@Co3O4 nanocomposites with abundant edge sites because the interface effect shows enhanced catalytic activities for oxygen evolution reactions (OER).