In situ generated dual oxyanions enable bifunctional synergy to overcome dehydrogenation limitations in HMF...

Enhancing the dehydrogenation kinetics of both electrocatalysts and the substrate is crucial for the electrooxidation of biomass-derived 5-hydroxymethylfurfural (HMF) to high-value 2,5-furandicarboxylic acid. Herein, we develop a dual oxyanion co-adsorption strategy by constructing a Mo-doped Ni₃S₂-modified Ni(OH) _x electrocatalyst (denoted as Mo-Ni₃S₂/Ni(OH) _x ), enabling the simultaneous adsorption of in situ generated SO₄ ^2- and MoO₄ ^2- oxyanions on the Ni(OH) _x surface. Experimental results and theoretical calculations demonstrate the distinct and synergistic role of co-adsorbed oxyanions in promoting HMF oxidation: (i) SO₄ ^2- primarily lowers the energy barrier for Ni(OH)₂ dehydrogenation, accelerating the formation of active Ni³⁺ species; and (ii) MoO₄ ^2- predominantly interacts with hydrogen atoms of HMF, reducing the adsorption energy of HMF and facilitating its dehydrogenation kinetics. Taking advantage of this bifunctional synergy, Mo-Ni₃S₂/Ni(OH) _x achieves a current density of 100 mA cm^-2 at 1.46 V vs. RHE, 2.5 times higher than that of the Ni₃S₂/Ni(OH) _x reference with only SO₄ ^2- adsorption. This synergy also allows Mo-Ni₃S₂/Ni(OH) _x to outperform Ni₃S₂/Ni(OH) _x in terms of electrochemical activity during the oxidation of other nucleophiles. Remarkably, it demonstrates satisfactory practical applicability in an integrated membrane electrode assembly (MEA) electrolyzer, achieving near 100% FDCA selectivity after 20 cycles at 1.9 V. In contrast, exogenously added oxyanions show a markedly weaker promotional effect due to competitive adsorption with HMF and OH^- at the active sites. This work elucidates the regulatory mechanism of similar oxyanions in a complex co-adsorption system for HMF oxidation and offers a rational strategy for designing efficient electrocatalysts for biomass valorization.