Water electrolysis consists of two electrochemical half-reactions: the hydrogen evolution reaction (HER) to produce hydrogen at the cathode and the OER to evolve oxygen at the anode, respectively. While the HER is a relatively straightforward two-electron transfer process, the main bottleneck is the sluggish four-electron OER that limits the overall efficiency of water electrolysis. [2,3] Currently, the common and matured industrialized electrolyzers to produce hydrogen rely on either acidic (proton-exchange membrane) or alkaline conditions. Out of which, alkaline electrolyzers are of particular importance as they use low-cost and earth-abundant materials to make the system fully sustainable and economically competitive. [4] As stated above, in order to increase the efficiency of the electrolyzers, improved anodes with high intrinsic activity are required. Notably, for alkaline electrolyzers, Ni-based materials have been the typical choice as anode (OER) materials because of their cost-effectiveness, high elemental abundance, good resistance to corrosive solutions, and low toxicity. [5,6] In recent years, significant progress has been achieved in the design, synthesis, and development of a variety of highly efficient Ni-based electrocatalysts involving oxides/hydroxides, chalcogenides, pnictides, alloys, and even metal-organic frameworks for OER at the lab scale to minimize the energetic losses in alkaline electrolysis. [6][7][8][9][10][11] Besides, significant efforts have been made to modify Ni-based electrocatalysts through heterostructure formation, oxygendefect generation, doping with heteroatoms, as well as phase and morphology engineering to attain technically viable efficiencies. However, further improvement beyond the current state of the art is required to enhance the overall OER performance. [9][10][11][12][13][14] Most of the Ni-based catalysts transform under the electrochemical alkaline conditions into electronically similar layered oxyhydroxide (LOH) phase with Ni III O x H y structure. [15,16] Similar to other transition-metal electrocatalysts, the OER activity of Ni-based catalysts largely depends on the defects, surface area, morphology, crystal structure of the precatalyst (e.g., NiNi distances), amount of edge/corner-sharing [NiO 6 ] units, size of the crystallite domain, etc. of the transformed Ni III O x H y phases,The development of novel earth-abundant metal-based catalysts to accelerate the sluggish oxygen evolution reaction (OER) is crucial for the process of large-scale production of green hydrogen. To solve this bottleneck, herein, a simple one-pot colloidal approach is reported to yield crystalline intermetallic nickel silicide (Ni 2 Si), which results in a promising precatalyst for anodic OER. Subsequently, an anodic-coupled electrosynthesis for the selective oxidation of organic amines (as sacrificial proton donating agents) to value-added organocyanides is established to boost the cathodic reaction. A partial transformation of the Ni 2 Si intermetallic precatalyst generates a poro...
The oxygen evolution reaction (OER) and the value‐added oxidation of renewable organic substrates are critical to supply electrons and protons for the synthesis of sustainable fuels. To meet industrial requirements, new methods for a simple, fast, environmental‐friendly and cheap synthesis of robust, self‐supported and high surface area electrodes are required. Herein, a novel in‐liquid plasma (plasma electrolysis) approach for the growth of hierarchical nanostructures on nickel foam is reported on. Under morphology retention, iron can be doped into this high surface area electrode. For the oxidation of 5‐(hydroxymethyl)furfural and benzyl alcohol, the iron‐free, plasma‐treated electrode is more suitable reaching current densities up to 800 mA cm−2 with Faradaic efficiencies above 95%. For the OER, the iron‐doped nickel foam electrode reaches the industrially relevant current density of 500 mA cm−2 at 1.473 ± 0.013 VRHE (60 °C) and shows no activity decrease over 140 h. The different effects of iron doping are rationalized using methanol probing and in situ Raman spectroscopy. Furthermore, the intrinsic activity is separated from the number of active sites, and, for the organic oxidation reactions, diffusion limitations are revealed. The authors anticipate that the plasma modified nickel foam will be suitable for various (electro)catalytic processes.
The oxygen evolution reaction (OER) and the value-added selective oxidation of renewable organic substrates are the most promising reactions to supply electrons and protons for the synthesis of sustainable fuels. To meet industrial requirements, new methods for a simple, fast, environmentally friendly, and cheap synthesis of robust, self-supported, high surface area electrodes are required. Herein, we report on a novel in liquid plasma electrolysis approach for the growth of hierarchical nanostructures on nickel foam. Under retention of the morphology, iron could be incorporated into this high surface area electrode. For the oxidation of 5-hydroxymethylfurfural and benzyl alcohol, the iron free plasma treated electrode is more suitable reaching current densities up to 800 mA/cm² with Faradaic efficiencies above 95%. For the OER, the iron incorporated nickel foam electrode reached the industrially relevant current density of 500 mA/cm² at 1.473±0.013 VRHE (60 °C) and showed no activity decrease over 140 h. The different effects of the iron doping is rationalised using MeOH doping and in situ Raman spectroscopy. Furthermore, we could separate changes in intrinsic activity per active site and number of active sites for the OER as well as reveal diffusion limitations of the organic oxidation reactions which we explain with respect to the surface morphology. We anticipate that the plasma modified high surface area nickel foam could potentially be applied for various electrocatalytic processes.
Triphenylphosphine (TPP) is one of the crucial reagents in Wittig olefination reactions. As part of the reaction, TPP will be sacrificed to yield the desired olefin (E/Z) as well as triphenylphosphine oxide (TPPO) containing a strong oxygen− phosphorus double bond (P�O). TPPO is considered thermodynamically stable but economically undesired. Conventional chemical recycling methods to reduce P V to P ΙΙΙ utilize sacrificial reduction agents (silanes, boranes, and allanes). In recent years, many studies have focused on less toxic and sacrificial-agent-free alternative pathways. This study focuses on the optimization of an indirect electrochemical reduction of TPPO toward TPP, which becomes possible after the activation of TPPO with methyl triflate. Under optimized conditions, the P�O bond of TPPO is weakened to allow a current efficiency of up to 50% and a chemical selectivity of 99%.
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