In-Liquid Plasma Modified Nickel Foam: NiOOH/NiFeOOH Active Site Multiplication for Electrocatalytic Alcohol, Aldehyde, and Water Oxidation

Abstract

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.

Effect of Surface‐Adsorbed and Intercalated (Oxy)anions on the Oxygen Evolution Reaction

“…Nevertheless, some reports have shown that the detour of in-situ OER interlayer species exchange by carbonate or alkaline hydroxide can be beneficial for the catalytic activity, and as such in-situ formed catalysts have been demonstrated to be more active than the same directly synthesized carbonate intercalated materials. [59,60,63,64,[68][69][70][71] This is especially the case for large intercalated species that strongly increase the d-spacing like dodecylsulfate (d-spacing > 20 Å), [64,65,69] Intercalated species (Pre)catalyst phase [a] and reference Comments Acetaldehyde C 2 H 4 O CoFe-LDH [81] Alkoxides C n H m O À NiFe LDH, [82] CoFe-LDH, [81] NiEt 2 , [26] Co(Fe)OHMe [27] Alkoxides likely oxidize under OER conditions, [83] alkoxide can replace the OH groups of LDH [26,27] Benzoate C 7 H 5 O 2 À Co-LDH, [68,73] Ni-LDH [72] d-spacing…”

Synergistic effects of vanadium incorporation in cobalt-based LDH on electron and proton transfer during electrocatalytic benzyl alcohol oxidation

“…16 The literature has highlighted that Ni-, and Co-containing LDHs, as the electrocatalysts, can notably augment the electrochemical performance of the BOR. 17,18 Evidence from prior research indicates that the higher oxidation states of Co or Ni species, observable only at elevated oxidation potentials, serve as the active sites for such electrochemical organic oxidations, including the BOR. [19][20][21] A careful approach to catalyst design, complemented by the fine-tuning of both the active catalytic sites and the electron transfer mechanism, is imperative.…”