ABSTRACT
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 (Ni2+ to Ni3+), 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 (Ni3+ to Ni2+), 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.
ABSTRACT
Electrochemical water splitting to generate hydrogen energy fills a gap in the intermittency issues for wind and sunlight power. Transition metal (TM) oxides have attracted significant interest in water oxidation due to their availability and excellent activity. Typically, the transitional metal oxyhydroxides species derived from these metal oxides are often acknowledged as the real catalytic species, due to the irreversible structural reconstruction. Hence, in order to innovatively design new catalyst, it is necessary to provide a comprehensive understanding for the origin of surface reconstruction. In this review, the most recent developments in the reconstruction of transition metal-based oxygen evolution reaction electrocatalysts were introduced, and various chemical driving forces behind the reconstruction mechanism were discussed. At the same time, specific strategies for modulating pre-catalysts to achieve controllable reconfiguration, such as metal substituting, increase of structural defect sites, were summarized. At last, the issues for the further understanding and optimization of transition metal oxides compositions based on structural reconstruction were provided.
ABSTRACT
It is extremely crucial to design and match high-quality cathode and anode for achieving high-performance asymmetric supercapacitors (ASCs). Herein, Co3 (PO4 )2 @NiCo-LDH/Ni foam (CP@NCOH/NF) cathode with hierarchical morphology and graphene hydrogel/Fe-Ni phosphide/Ni foam (GH/FNP/NF) anode with the robust and porous structure are elaborately designed and prepared, respectively. Owing to their unique and profitable structures, both CP@NCOH/NF and GH/FNP/NF electrodes yield the superior capacity (10760 and 2236 mC cm-2 at 2 mA cm-2 , respectively), good rate capability (63% retention at 200 mA cm-2 and 52% retention at 50 mA cm-2 , respectively), and excellent cycling stability (72% and 74% retention after 10 000 cycles, respectively). Benefiting from their matchable electrochemical performances, the configured solid-state CP@NCOH/NF//GH/FNP/NF ASC outputs both competitive energy density (80.2 Wh kg-1 /4.1 mWh cm-3 ) and power density (14563 W kg-1 /750 mW cm-3 ), companied by remarkable cyclability (71% retention after 10 000 cycles), manifesting its great promise for large-scale integrated energy-storage system.
