Interfacial molybdate-enabled electric field deconfinement to passivate water oxidation for wide-potential biomass electrooxidation

Abstract

The priority adsorption of OH⁻ in the anodic refining process typically compromises the accessibility of organic reactants and propels their competing oxygen evolution reaction (OER), inevitably generating inactive areas of organics electrooxidation. In this work, an electric field deconfinement strategy enabled by self-originated MoO₄²⁻ was unveiled to confine the mass diffusion of OH⁻ over a Mo-modulated Ni-based electrode (NiMoO_x/NF). The reconstructable NiMoO_x/NF catalyst was high-efficiency for selective electrooxidation of various biomass derivatives, especially for electrocatalytic 5-hydroxymethylfurfural (HMF) oxidation reaction (e-HMFOR) to afford 2,5-furanedicarboxylic acid (FDCA, a versatile bioplastic monomer). In-situ tests and finite element analyses evidenced that NiOOH-MoO₄²⁻ in-situ reconstructed from NiMoO_x/NF is responsible for e-HMFOR, where the surface-adsorbed MoO₄²⁻ can trigger a negative electric field to restrict OH⁻ affinity by electrostatic repulsion but facilitate HMF adsorption, thereby leading to the deteriorated OER and enhanced e-HMFOR. Theoretical calculations further elaborated that introduced MoO₄²⁻ boosts HMF adsorption to accelerate the reaction kinetics but elevates the energy barrier of O* coupling into OOH* to passivate OER. As a result, a wide potential interval (1.35–1.55 V_RHE) was applicable to produce FDCA via e-HMFOR with admirable productivity (95.4–97.8% faradaic efficiencies), rivaling the state-of-the-art Ni-based electrodes. In addition, the established membrane electrode assembly electrolyzer could be operated stably for 40 h at least, with high efficiency in electrosynthesis of gram-grade FDCA. This study underlines the viability and criticality of electric field deconfinement for manipulating the OH⁻ adsorption to facilitate organics electrooxidation and biorefinery while getting rid of competing reactions.