In Co 3 O 4 systems, the oxygen vacancy is reported to improve the oxygen evolution reaction (OER) activity because of higher Co 2+ /Co 3+ surface ratio. In situ studies have revealed Co 3+ site reducibility as the key factor for OER activity of cobalt oxide-based systems. In this context, we have synthesized and analyzed OER activity of two Co 3 O 4 systems; c-Co 3 O 4 with higher oxygen defects or Co 2+ /Co 3+ ratio and n-Co 3 O 4 with relatively less Co 2+ /Co 3+ ratio but more Co 3+ reducibility. The systems, n-and c-Co 3 O 4 show overpotential of 380 and 440 mV at 10 mA/cm 2 and Tafel slope of 153 and 53 mV/dec, respectively, for OER. Electrochemical characterization reveals that the lowering of OER onset potential is influenced by Co 3+ reducibility rather than defects in Co 3 O 4 systems while adsorption capacitance arising from surface irregularities, pores and their geometry, and Co 3+ -O h sites cause an increase in the Tafel slope values or decrease in OER kinetics. The correlation of the key factors such as Co 3+ reducibility and oxygen defects of two different Co 3 O 4 systems toward OER activity can aid the designing of highly efficient cobalt oxide-based OER catalysts. KEYWORDS: nanocrystalline cobalt oxide, Co 2+ /Co 3+ ratio, Co 3+ -O h reducibility, OER kinetics, impedance study
The electrochemical urea oxidation reaction (UOR) provides a cost-effective way of generating hydrogen owing to its low thermodynamic energy barrier. Although UOR is an effective way to generate hydrogen, sustained...
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