Enhancing Selective Electrooxidation of 5-Hydroxymethylfurfural via Coordinating the Contradictory Role of Fe in Ni(II)/Ni(III) Redox Kinetics
Yue Xiao, Ziqi Zhao, Pengfei Long, Jingya Zhang, Zongyuan Wang, Jichang Liu, Fuxi Bao
Abstract
Nickel-based materials have shown great potential as electrocatalysts for the 5-hydroxymethylfurfural oxidation reaction (HMFOR), owing to dynamic Ni 2+ /Ni 3+ redox cycling. However, this redox process, which is critical for HMFOR kinetics, is prone to disruption. For example, Fe plays a paradoxical role: it facilitates the reduction of Ni 3+ but simultaneously inhibits the oxidation of Ni 2+ . Here, we develop a hybrid electrocatalyst consisting of Ni(OH) 2 /NiFeO x H y nanosheets supported on nickel foam (denoted as Ni(OH) 2 /NiFeO x H y /NF), which exhibits satisfactory HMFOR performance, achieving a current density of 204 mA cm –2 at 1.45 V vs RHE along with complete HMF conversion and 92% Faradaic efficiency over 20 cycles. We strategically leveraged Fe incorporation to enhance the proton-coupled electron transfer process during HMF dehydrogenation, a critical step facilitated by Ni 3+ reduction. This enhancement is attributed to the synergistic effect between NiFeO x H y and Ni(OH) 2, which enhances HMF adsorption and increases interfacial nucleophilicity, thereby facilitating the capture of protons released from HMF. Although Fe incorporation partially suppresses Ni 2+ oxidation, the abundant crystalline/amorphous boundaries, oxygen-deficient amorphous domains, and the integration of NiFeO x H y with Ni(OH) 2 collectively increase the number of active Ni sites and compensate for the inhibitory effect of Fe. Furthermore, we propose two HMFOR pathways involving hydroxyl groups and protons on the Ni(OH) 2 surface via Ni 2+ /Ni 3+ redox chemistry and identify proton deintercalation as the dominant pathway through density functional theory calculations. This work presents a distinctive strategy that not only enhances HMFOR kinetics by leveraging the dual role of Fe in Ni-based redox chemistry but is also potentially applicable to other biomass-derived substrates.