High-performance 5-hydroxymethylfurfural electrooxidation with a Mn-doped Ni oxyhydroxide catalyst: the coenhancement of proton deintercalcation and substrate adsorption

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 Ni 2+ 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 Ni 3+ (OH)O active center) and dramatically promote the adsorption ability of different reactive intermediates on Ni 3+ (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 CH 2 OH and HC O groups during HMFOR must require the participations of OH − ions and H 2 O 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.