Alkaline water electrolysis (AWE) is among the most developed technologiesfor green hydrogen generation. Despite the tremendous achievements in boosting the catalytic activity of the electrode, the operating current density of modern water electrolyzers is yet much lower than the emerging approaches such as the proton-exchange membrane water electrolysis (PEMWE). One of the dominant hindering factors is the high overpotentials induced by the gas bubbles. Herein, the bubble dynamics via creating the superaerophobic electrode assembly is optimized. The patterned Co-Ni phosphide/spinel oxide heterostructure shows complete wetting of water droplet with fast spreading time (≈300 ms) whereas complete underwater bubble repelling with 180°c ontact angle is achieved. Besides, the current collector/electrode interface is also modified by coating with aerophobic hydroxide on Ti current collector. Thus, in the zero-gap water electrolyzer test, a current density of 3.5 A cm −2 is obtained at 2.25 V and 85 °C in 6 m KOH, which is comparable with the state-of-the-art PEMWE using Pt-group metal catalyst. No major performance degradation or materials deterioration is observed after 330 h test. This approach reveals the importance of bubble management in modern AWE, offering a promising solution toward high-rate water electrolysis.
The NiOOH electrode is commonly used in electrochemical
alcohol
oxidations. Yet understanding the reaction mechanism is far from trivial.
In many cases, the difficulty lies in the decoupling of the overlapping
influence of chemical and electrochemical factors that not only govern
the reaction pathway but also the crystal structure of the in situ formed oxyhydroxide. Here, we use a different approach
to understand this system: we start with synthesizing pure forms of
the two oxyhydroxides, β-NiOOH and γ-NiOOH. Then, using
the oxidative dehydrogenation of three typical alcohols as the model
reactions, we examine the reactivity and selectivity of each oxyhydroxide.
While solvent has a clear effect on the reaction rate of β-NiOOH,
the observed selectivity was found to be unaffected and remained over
95% for the dehydrogenation of both primary and secondary alcohols
to aldehydes and ketones, respectively. Yet, high concentration of
OH– in aqueous solvent promoted the preferential
conversion of benzyl alcohol to benzoic acid. Thus, the formation
of carboxylic compounds in the electrochemical oxidation without alkaline
electrolyte is more likely to follow the direct electrochemical oxidation
pathway. Overoxidation of NiOOH from the β- to γ-phase
will affect the selectivity but not the reactivity with a sustained
>95% conversion. The mechanistic examinations comprising kinetic
isotope
effects, Hammett analysis, and spin trapping studies reveal that benzyl
alcohol is oxidatively dehydrogenated to benzaldehyde via two consecutive hydrogen atom transfer steps. This work offers the
unique oxidative and catalytic properties of NiOOH in alcohol oxidation
reactions, shedding light on the mechanistic understanding of the
electrochemical alcohol conversion using NiOOH-based electrodes.
The rational coupling of hydrothermal and electrodeposition approaches enables controlled synthesis of various CoP Nature-inspired nanostructures with distinct electrocatalytic performance.
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