An Acetate Bound Cobalt Oxide Catalyst for Water Oxidation: Role of Monovalent Anions and Cations In Lowering Overpotential

摘要

Co(II) dissolved in acetate buffer at pH 7 is found to be a good wateroxidation catalyst (WOC) showing electrocatalytic water oxidation currentsignificantly greater than Co(II) in phosphate buffer under the same conditionsowing to the higher solubility of the former. When electrodeposited on ITO/FTOelectrodes it forms acetate bound cobalt(II)oxide based material (Co-Ac-WOC)showing catalytic water oxidation current density of 0.1 mA/cm$^{2}$ at 830 mVand 1 mA/cm$^{2}$ at 1 V in a pH 7 buffer solution. The morphology of Co-Ac-OECis investigated with AFM, HR-TEM and SEM (at different times andelectrodeposition potentials). The chemical composition of Co-Ac-OEC isinvestigated using XPS, EDX, combustion analysis and ATR-FTIR which indicatesthat this material has a CoO core with chloride and acetate anions bound to theCo center. Sodium is found to be integrated in the Co-Ac-WOC. The presence ofthe sodium ions and the chloride ions lowers the onset potential for oxygenevolution reaction (OER) by 240 mV relative to the classic Co-Pi at pH 7. Thelower onset potential and higher OER current lowers the exchange currentdensity to 10$^{-6.7}$ in Co-Ac-WOC relative to 10$^{-8}$-10$^{-10}$ in Co-Piand its derivatives.