Synthesis of MnO_x Water Oxidation Catalyst on Fluorine‐Doped Tin Oxide with a Dual‐Series Cyclic Voltammetry Method

Abstract

This Communication reports an ew methodf or synthesizing manganese-basedw ater oxidation catalysts in situ in aqueous media. The method provides powerful tunability of the electrodeposition process to enable independentc ontrol over the morphology of the catalytic film and the oxidation state of the catalyst. Our results show that the first cyclic voltammetry (CV) series produces af ilm with an anoscale fibrous structure, whereas the second CV series improves its catalytic performance by enhancing the oxidation state of the film without damaging the existing surfacem orphology.S canning electron microscopy and transmission electron microscopyw ere used to characterize the morphologyo ft he MnO x film, CV was used to assess the catalyst functionality,a nd long-term amperometry was used to assess the stability.The use of artificial photosynthesis to produce hydrogen fuel has long been regarded as one of the most promising and sustainable solutions to the worldwide energy demand.[1] The process involves two main half-reactions:w ater oxidation to release hydrogeni ons and oxygen, and hydrogen-ion reconstitution to produce hydrogen fuel.[2] The water oxidation reaction is the rate-limiting step in this process, because its large overpotentiali sasignificant energy barrier. [3] In the past, Ru-and Ir-based catalysts have been used for this reaction, but the cost of these rare earth elements greatly limit their use on al arge scale.[4] Within the past decade, different water oxidation catalysts( WOCs) based on inexpensive and abundant materials have been developed to replace the precious metal oxides, including the successful "Co-Pi" catalyst of Kanan and Nocera.[5] This cobalt-based catalyst, used to generate an "artificial leaf", is easy to synthesize in situ and has excellent catalytic performance.[6] Our group has similarly demonstrated that ac obalt-based catalysts ynthesized ex situ and deposited on ac onductive surface retains its activity toward water oxidation.[7] Although work on cobalt-based water oxidation catalysts continues, manganese-based WOCs have recently become the focus of much research, because of severalt unable and unique attributes. Manganese is not ar are earth element, and its complexes are largely nontoxic.[8] Equally important, manganese is the primary elementi nt he natural oxygen evolvingc enter (OEC) of plants and, in general, manganesebased WOCs have highere fficiencies and longere ffective lifetimes. [9] Various methods have been reported for synthesizing manganese-based water splitting complexes, both ex situ [10] and in situ.[11] Among these, electrodeposition has the benefito f simplicity in experimental setup along with easily controllable deposition conditions. Typically,e lectrodeposition has been performedb yu sing chronoamperometry [12] or as ingle series of cyclic voltammetry (CV). [13] In this work, we explored the use of multiple CV series for the electrodeposition of aM nO x catalyst on fluorine-doped tin oxide (FTO) with the aim to produce ac atalytic film with ah ig...

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Electrodeposition of Ni/Ni(OH)2 Catalytic Films for the Hydrogen Evolution Reaction Produced by using Cyclic Voltammetry

“…In contrast, we have recently synthesized MnO x water oxidation catalysts through dual‐series cyclic voltammetry (CV) over different potential ranges. This novel method has enabled us to produce catalysts with a nanoscale fibrous structure that exhibits excellent and stable performance towards water oxidation …”

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