Constructing Ultrathin In-Plane Phase-Junctions in Nickel Hydroxide Nanosheets for Selective Electro-Oxidation of Methanol to Formate Coupled with Hydrogen Evolution.

Developing highly efficient nickel-based electrocatalysts toward the methanol oxidation reaction (MOR) is of considerable significance for energy conversion and chemical synthesis, yet it is still a challenging issue. Herein, we developed a facile in situ phase transformation strategy to construct in-plane phase-junctions in ultrathin α/β-Ni(OH)2 nanosheets as a high-performance electrocatalyst for the MOR. Specially, the role of in-plane phase-junctions played in the MOR process was deeply clarified through the combination of experimental and theoretical studies. In situ Fourier transform infrared spectroscopy indicates that the MOR process concurrently involves the formate-forming and CO-forming pathways over the α/β-Ni(OH)2 electrode. In situ Raman spectroscopy reveals that NiOOH species originating from the dehydrogenation of Ni(OH)2 are electroactive sites for the MOR. Density functional theory calculations disclose that the construction of in-plane phase-junctions can not only improve the charge-transfer capacity, but also endow Ni(OH)2 with enhanced ability to generate NiOOH species and adsorb methanol molecules, enabling more advantageous kinetics for the MOR. Therefore, the prepared α/β-Ni(OH)2 nanosheets show excellent electrocatalytic MOR activity and stability, exhibiting high performance for formate production up to 94.1% faradaic efficiency at 0.45 V vs Ag/AgCl. This work highlights the crucial efficacy of the phase-junction in the electrochemical MOR process for biomass valorization.