<i>In-Liquid</i> Plasma-Mediated Manganese Oxide Electrocatalysts for Quasi-Industrial Water Oxidation and Selective Dehydrogenation.

Mondal, Indranil; Menezes, Pramod V; Laun, Konstantin; Diemant, Thomas; Al-Shakran, Mohammad; Zebger, Ingo; Jacob, Timo; Driess, Matthias et al. · ACS Nano · 2023

basic_science · Level V

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Abstract

The production of renewable feedstocks through the coupled oxygen evolution reaction (OER) with selective organic oxidation requires a perfect balance in the choice of a catalyst and its synthesis access, morphology, and catalytic activity. Herein we report a rapid <i>in-liquid</i> plasma approach to produce a hierarchical amorphous birnessite-type manganese oxide layer on 3D nickel foam. The as-prepared anode exhibits an OER activity with overpotentials of 220, 250, and 270 mV for 100, 500, and 1000 mA·cm<sup>-2</sup>, respectively, and can spontaneously be paired with chemoselective dehydrogenation of benzylamine under both ambient and industrial (6 M KOH, 65 °C) alkaline conditions. The in-depth <i>ex-situ</i> and <i>in-situ</i> characterization unequivocally demonstrate the intercalation of potassium in the birnessite-type phase with prevalent Mn<sup>III</sup> states as an active structure, which displays a trade-off between porous morphology and bulk volume catalytic activity. Further, a structure-activity relationship is realized based on the cation size and structurally similar manganese oxide polymorphs. The presented method is a substantial step forward in developing a robust MnO<sub><i>x</i></sub> catalyst for combining effective industrial OER and value-added organic oxidation.