Electrosynthesis of highly transparent cobalt oxide water oxidation catalyst films from cobalt aminopolycarboxylate complexes

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.

Engineering Disorder at a Nanoscale: A Combined TEM and XAS Investigation of Amorphous versus Nanocrystalline Sodium Birnessite

The term amorphous metal oxide is becoming widely used in the catalysis community. The term is generally used when there are no apparent peaks in an X-ray diffraction pattern. However, the absence of such features in X-ray diffraction can mean that the material is either truly amorphous or that it is better described as nanocrystalline. By coprecipitating a sodium birnessite-like phase with and without phosphate (1.5 %), we are able to engineer two very similar but distinct materials – one that is nanocrystalline and the other that is amorphous. The two closely related phases were characterized with both Mn K-edge X-ray absorption spectroscopy and high-resolution transmission electron microscopy. These structural results were then correlated with catalytic and electrocatalytic activities for water oxidation catalysis. In this case, the amorphous phosphate-doped material was less catalytically active than the nanocrystalline material.

Towards Global Artificial Photosynthesis (Global Solar Fuels): Energy, Nanochemistry, and Governance

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