Surface galvanic formation of Co-OH on Birnessite and its catalytic activity for the oxygen evolution reaction

Abstract

Low cost, high-efficient catalysts for water splitting can be potentially fulfilled by developing earth abundant metal oxides. In this work, surface galvanic formation of Co-OH on K_0.45MnO₂ (KMO) was achieved via the redox reaction of hydrated Co²⁺ with crystalline Mn⁴⁺. The synthesis method takes place at ambient temperature without using any surfactant agent or organic solvent, providing a clean, green route for the design of highly efficient catalysts. The redox reaction resulted in the formation of ultrathin Co-OH nanoflakes with high electrochemical surface area. X-ray adsorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) analysis confirmed the changes in the oxidation state of the bulk and surface species on the Co-OH nanoflakes supported on the KMO. The effect of the anions, chloride, nitrate and sulfate, on the preparation of the catalyst was evaluated by electrochemical and spectrochemical means. XPS and Time of flight secondary ion mass spectrometry (ToF-SIMS) analysis demonstrated that the layer of CoO_xH_y deposited on the KMO and its electronic structure strongly depends on the anion of the precursor used during the synthesis of the catalyst. In particular, it was found that Cl favors the formation of Co-OH, changing the rate determining step of the reaction, which enhances the catalytic activity towards the OER, producing the most active OER catalyst in alkaline media.

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Identifiers

ORCID for Andrea E. Russell: orcid.org/0000-0002-8382-6443

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