High-performance 5-hydroxymethylfurfural electrooxidation with a Mn-doped Ni oxyhydroxide catalyst: the coenhancement...

The electrocatalytic 5-hydroxymethylfurfural oxidation reaction (HMFOR) has become a clean and fast-response route for synthesizing the sustainable biomonomer. Here, a Mn-doped Ni(OH)₂ catalyst is constructed and enables a 98.9% yield of 2,5-furandicarboxylic acid and a 99% Faradic efficiency with a stable durability up to 50 cycles for the alkaline HMFOR. The Mn-Ni(OH)₂ catalyst shows a low onset potential of ca. 1.29 V (vs. reversible hydrogen electrode, RHE) and achieves a current density of 50 mA cm^-2 at only 1.38 V in 1 M KOH, significantly outperforming the vast majority of Ni-based (oxy)hydroxide catalysts reported to date in the literature. The isomorphic substitution of Ni²⁺ ions by the coordination unsaturated Mn ions brings about lattice expansions and crystal defects of the nanoflower-shaped Ni(OH)₂ catalyst. The distinctive Mn-doping effect can modulate the electronic structure and also oxygen vacancy formation on Ni(OH)₂ surface. The experimental and theoretical studies systematically unravel that the ingenious catalytic synergism can significantly boost the proton deintercalation feature of Ni(OH)₂ (i.e., an improved generation kinetics of the Ni³⁺(OH)O active center) and dramatically promote the adsorption ability of different reactive intermediates on Ni³⁺(OH)O. As a result, HMFOR is greatly enhanced on the as-prepared Mn-Ni(OH)₂ catalyst. The mechanism investigations further evidence that the activation processes of CH₂OH and HCO groups during HMFOR must require the participations of OH^- ions and H₂O molecules, respectively. This work has clearly tracked the reconstruction process of a Ni electrocatalyst and firstly unlocked the activation behaviors of different functional groups, thus successfully getting deep insights into the real and dynamic catalytic mechanism for the alkaline HMFOR.