Electrosynthesis of Highly Transparent Cobalt Oxide Water Oxidation Catalyst Films from Cobalt Aminopolycarboxylate Complexes

Abstract

Efficient catalysis of water oxidation represents one of the major challenges en route to efficient sunlight-driven water splitting. Cobalt oxides (CoOx ) have been widely investigated as water oxidation catalysts, although the incorporation of these materials into photoelectrochemical devices has been hindered by a lack of transparency. Herein, the electrosynthesis of transparent CoOx catalyst films is described by utilizing cobalt(II) aminopolycarboxylate complexes as precursors to the oxide. These complexes allow control over the deposition rate and morphology to enable the production of thin, catalytic CoOx films on a conductive substrate, which can be exploited in integrated photoelectrochemical devices. Notably, under a bias of 1.0 V (vs. Ag/AgCl), the film deposited from [Co(NTA)(OH2 )2 ](-) (NTA=nitrilotriacetate) decreased the transmission by only 10 % at λ=500 nm, but still generated >80 % of the water oxidation current produced by a [Co(OH2 )6 ](2+) -derived oxide film whose transmission was only 40 % at λ=500 nm.

Robust Sub‐Monolayers of Co3O4 Nano‐Islands: A Highly Transparent Morphology for Efficient Water Oxidation Catalysis

“…This is among the highest reported so far for Co‐based electrocatalysts (Table ) and translates to a per‐metal TOF of 0.38–0.62 s −1 . It was reported by Bonke et al that highly active electrochemically deposited CoO x reached a TOF of 0.14 s −1 at an overpotential of 400 mV (pH 9.2) and transmission of ≈88% . With respect to Co 3 O 4 ‐based catalysts, here, the per‐metal TOFs are about two orders of magnitude higher than most of the works in Table and slightly better than that recently reported by Müller and co‐workers with a five times smaller (6.5 nm) Co 3 O 4 particle size .…”

“…Several materials, including electrochemically deposited NiFeO x , and CoO x , sputtered NiO x ,[4b] and surface‐modified Cu metal electrodes have been recently investigated as transparent electrocatalysts for water oxidation. Among these, cobalt oxide electrocatalysts have been reported to significantly improve the photoelectrochemical performance and the long‐term photostability of metal oxide light absorbers, such as hematite, TaON, and WO 3 .…”

First row transition metal catalysts for solar-driven water oxidation produced by electrodeposition

“…The films thus produced were competent hydrogen evolution electrocatalysts, but of more relevance to the current discussion is their use as catalysts of the OER. 40 The use of such precursors was held to allow control over the deposition rate and morphology of the films thus produced and hence to enable the production of thin catalyst films on the conductive substrate. In the case of a photoelectrode generated using a cobalt-nitrilotriacetate complex as the Co source, this strategy resulted in a film that absorbed only 10% of the incident light whilst still generating >80% of the water oxidation current produced by a film derived from the simple [Co(OH 2 ) 6 ] 2+ cation (whose transmission was only 40% at those same wavelengths).…”

Electrolysis of Natural Waters Contaminated with Transition‐Metal Ions: Identification of A Metastable FePb‐Based Oxygen‐Evolution Catalyst Operating in Weakly Acidic Solutions

“…The in situ generation of water electrooxidation catalysts was attempted in the examined water samples with added supporting electrolyte by applying positive potentials, following a well‐established strategy of generating “self‐healing” electrocatalysts . This was undertaken in both potentiodynamic (voltammetric) and potentiostatic (chronoamperometric) modes, since, for example, deposition of “active” MnO x catalysts requires cycling the potential, while efficient CoO x and NiO x can be formed in both regimes .…”