Unveiling the Pivotal Role of d x2-y2 Electronic States in Nickel-Based Hydroxide Electrocatalysts for Methanol Oxidation.

The anodic methanol oxidation reaction (MOR) plays a crucial role in coupling with the cathodic hydrogen evolution reaction (HER) and enables the sustainable production of the high-valued formate. Nickel-based hydroxide (Ni(OH) 2 ) as MOR electrocatalyst has attracted enormous attention. However, the key factor determining the intrinsic catalytic activity remains unknown, which significantly hinders the further development of Ni(OH) 2 electrocatalyst. Here, we found that the d x 2 - y 2 ${{d}_{{x}^{2}-{y}^{2}}}$ electronic state within antibonding bands plays a decisive role in the whole MOR process. The onset potential depends on the deprotonation ability (Ni 2+ to Ni 3+ ), which was closely related to the band center of d x 2 - y 2 ${{d}_{{x}^{2}-{y}^{2}}}$ orbital. The closer of d x 2 - y 2 ${{d}_{{x}^{2}-{y}^{2}}}$ orbital to the Fermi level showed the stronger the deprotonation ability. Meanwhile, in the high potential region, the broadening of d x 2 - y 2 ${{d}_{{x}^{2}-{y}^{2}}}$ orbital would facilitate the electron transfer from methanol to catalysts (Ni 3+ to Ni 2+ ), further enhancing the catalytic properties. Our work for the first time clarifies the intrinsic relationship between d x 2 - y 2 ${{d}_{{x}^{2}-{y}^{2}}}$ electronic state and the MOR activities, which adds a new layer of understanding to the methanol electrooxidation research scene.