A Bimetallic Phosphide@Hydroxide Interface for High-Performance 5-Hydroxymethylfurfural Electro-Valorization

Replacing the oxygen evolution reaction with alternative low-overpotential anodic reactions is promising to decrease the cell voltage of overall water splitting. Particularly, once the selected anodic reaction is controllable to generate value-added chemicals, the cell can generate various valuable products at the anode as well as green hydrogen at the cathode. So far, such a “One Stone Two Birds” strategy has been widely explored. Herein, we focus on the 5-hydroxymethylfurfural oxidation reaction (HMFOR) to generate 2,5-furandicarboxylic acid (FDCA) as the selected anodic reaction. At present, nonprecious transition metal oxides and hydroxides have shown excellent intrinsic activity toward this reaction. However, the metal oxide and hydroxide catalysts are limited by their low electronic conductivity, particularly if the catalyst layers are thick. Triggered by the reconstruction phenomenon of metal phosphide catalysts under anodic reaction conditions as revealed in our recent work, we further design an artificial dense NiFe(OH)_x layer on the NiFeP substrate, i.e., a NiFeP@NiFe(OH)_x interface. The NiFeP core is more electronically conductive to compensate for the low conductivity of active NiFe(OH)_x; on the other hand, the intended NiFe(OH)_x layer efficiently protects the NiFeP core against further oxidation and reconstruction. The NiFeP@NiFe(OH)_x catalyst thus demonstrates a better HMFOR activity than the reference NiFe(OH)_x catalyst and is stable during the HMFOR process. This work suggests an interface engineering strategy to design and synthesize advanced catalysts for the anodic HMFOR and beyond.