Controlled electrodeposited cobalt phases for efficient OER catalysis, RRDE and eQCM studies

Different cobalt phases are deposited on graphite discs from CoSO4 baths in absence and presence of equimolar concentration of citrate ions, Co/G and Co-(cit)/G, respectively. The prepared electrodes are subjected to different electrochemical studies. Benchmark recommends the use of the overpotential required to achieve current density of 10 mA.cm(-2) (eta(t=0)) in linear sweep voltammetry, LSV, at 10 mV.s(-1) as an activity parameter for oxygen evolution reaction, OER. The values of eta(t=0) equal 0.443 and 0.440 for Co/G and Co-(cit)/G, respectively. This work suggests an activation routine based on the observed sequential enhancing of eta(t=0) values through successive cyclic voltammetry in 1 M NaOH. Satisfactory eta(t=0) values of 0.437 and 0.394 V are obtained for the activated electrodes prepared in absence and presence of citrate anions, respectively. All the prepared electrodes show noteworthy stability over 2hrs. The values of overpotential after 2 hrs eta(t)(=)(2h) in 1 M NaOH reveals higher efficiency for the electrodes prepared from citrate-containing bath rather than citrate free bath. The morphology and the structure of the optimum electrodes are characterized. RRDE and eQCM studies clarify the role of the citrate anion in controlling the deposited cobalt phases. The OER catalytic activities are correlated with the deposited cobalt phase structure for the prepared electrodes. (C) 2019 Elsevier Ltd. All rights reserved.