Unlocking d-Orbital Tunability in Nickel-Based Hydroxide by High-Entropy Strategy for Boosting Electrocatalytic 5-Hydroxymethylfurfural Oxidation

Abstract

Electrocatalytic 5-hydroxymethylfurfural oxidation reaction (HMFOR) offers a sustainable and green route for upgrading biomass-derived chemicals and substituting energy-intensive oxygen evolution reaction. Nickel-based hydroxides are famous HMFOR electrocatalysts, whose activities are closely correlated with their electronic structures near Fermi level. Recent advances identify lattice distortion as a crucial factor affecting the electronic structures of nickel-based hydroxides, thereby governing the electrocatalytic performance. Herein, we report the modulated d-orbital electronic state of Ni active sites in NiCoMnCrCu hydroxide via a high-entropy strategy, which induces lattice distortion that disrupts the NiO6 octahedron symmetry. The distortion moves up the dx2-y2 orbital of the Ni2+ state closer to Fermi level to promote the deprotonation step for generating reconstructed active sites. Meanwhile, it broadens the dx2-y2 orbital of the Ni3+ state, which facilitates the electron transfer between reactants and catalyst in the spontaneous chemical reaction. Hence, the high-entropy hydroxide displays superior HMFOR performance with a low onset of 1.334 V vs. RHE, while selectively converting HMF into 2,5-furandicarboxylic acid (FDCA) with a high Faradaic efficiency (above 90%) and fast production rate (2178.3 μmol cm-2 h-1). When employed in a flow cell for coupled biomass upgrading and hydrogen production, the system enables steady co-production of value-added FDCA and energy-saving hydrogen. The present study provides insights into modulating the electronic states of active sites via high-entropy strategy.