Heterostructure engineering of the N-doped NiMoO4 two-phase electrocatalyst for industrial large-scale synthesis of 2,5-furan dicarboxylic acid†

Abstract

Ambient electrosynthesis of value-added 2,5-furan dicarboxylic acid (FDCA) from the selective oxidation of 5-hydroxymethylfurfural (HMF) demonstrates a green, eco-friendly and promising alternative method to the traditional energy-intensive synthesis of fuels and chemicals for biomass industrial utilization. However, it is challenging and crucial to further explore highly efficient and durable electrocatalysts via large-scale synthesis toward the HMF electrocatalytic oxidation reaction (HMFOR) to FDCA, a polyethylene glycol 2,5-furanodicarboxylate precursor, for commercial applications. Herein, a unique N-doped two-phase NiMoO₄ heterostructure, namely, NiMoO₄ and NiMoO₄·H₂O, is easily fabricated via the conversion of Ni₂(NO₃)₂(OH)₂ on nickel foam (NiNH/NF) in an aqueous solution containing ammonium molybdate under hydrothermal conditions, where Ni₂(NO₃)₂(OH)₂ is prepared on a nickel foam substrate by a molten metal salt method. This N-doped two phase NiMoO₄ heterostructure (N–NiMoO₄/NF) as an anode exhibits remarkable HMFOR activity; at potentials of 1.43 V and 1.48 V (vs. RHE), the current density can reach 100 mA cm⁻² and 150 mA cm⁻², respectively. Its conversion rate of HMF, FDCA yield and faradaic efficiency (FE) over the N–NiMoO₄ electrocatalyst are close to 100% after 9 cycles at 1.52 V. The outstanding HMFOR performance should be due to the fact that this NiMoO₄ heterostructure with nanorods integrated onto nanosheets exhibits a large surface area and optimizes the competitive adsorption to HMF and OH- via metal active sites and oxygen vacancies promoted interfacial charge transfer. As a result, this N-doped α,β-NiMoO₄ electrode affords a gram-scale FDCA in a homemade reactor, demonstrating its large-scale practical industrial feasibility.