Electrocatalytic activity of electrodeposited cobalt oxide films to produce oxygen gas from water

•A cobalt oxide catalyst film for water oxidation was prepared by electrodeposition.•Catalytic activities were measured in alkaline and neutral aqueous solutions.•By heating treatment, the catalytic activities increased to about twice.

An electrocatalytic cobalt oxide film for water oxidation was prepared on an indium tin oxide (ITO)-coated substrate by anodic electrodeposition. Atomic force microscopy measurements revealed that numerous particles with a diameter of 100–250 nm were uniformly dispersed on the ITO substrate and the particle size increased when prepared at higher temperature. Cyclic voltammograms of the Co oxide-coated ITO electrodes were measured in alkaline and neutral aqueous solutions to examine their redox characteristics and ability to catalyze water oxidation. When Co oxide was electrodeposited from solutions kept at 10, 25 and 50 °C, the amount of electroactive Co oxide per unit area (Γea) was 1.06 × 10−8, 1.72 × 10−8, and 2.31 × 10−8 mol cm−2, respectively. The increase in Γea accompanied the increase in particle size observed with rising deposition temperature. Quantitative analyses of O2 gas produced by water electrolysis were carried out under potentiostatic conditions using these Co oxide-modified electrodes and a bare ITO electrode for comparison. For the Co oxide-coated electrode prepared at 10 °C, the amount of O2 evolved by electrolysis for 2 h at 1.3 V vs. Ag/AgCl was 1.3 × 10−5 mol cm−2 in alkaline electrolyte solution and 1.52 × 10−5 mol cm−2 in neutral electrolyte solution containing phosphate ions. In addition, when the Co oxide-coated electrode treated at 450 °C was used, the amount of O2 evolved by the electrolysis increased to 2.58 × 10−5 mol cm−2 in the neutral electrolyte solution containing phosphate ions, resulting from a stable catalytic current.

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