Template-based synthesis of Co3O4 and Co3O4/SnO2 bifunctional catalysts with enhanced electrocatalytic properties for reversible oxygen evolution and reduction reaction.

Porous cobalt (III) oxide (Co 3 O 4) and mixed cobalt (III) oxide - tin oxide (Co 3 O 4 /SnO 2) were prepared by a novel template-based hydrothermal method resulting in their spherical morphology as confirmed by thorough physico-chemical characterisation. Two oxides were systematically examined as bifunctional electrocatalysts for oxygen reduction (ORR) and evolution (OER) reaction in alkaline media by voltammetry with rotating disk electrode, electrochemical impedance spectroscopy, and chronoamperometry. Low-cost Co 3 O 4 and Co 3 O 4 /SnO 2 electrocatalysts showed excellent ORR performance with low onset and half-wave potential, low Tafel slope, and the number of exchange electrons near 4, comparable to the commercial Pt/C electrocatalyst. Low OER onset potential of 1.52 and 1.57 V was observed for Co 3 O 4 and Co 3 O 4 /SnO 2 , respectively, with low charge transfer resistance under anodic polarization conditions. Finally, to test bifunctional activity and durability of the two electrocatalyst, switch OER/ORR test was carried out. [Display omitted] • Spherical Co 3 O 4 and Co 3 O 4 /SnO 2 were synthesized by the hydrothermal method. • Both electrocatalysts showed excellent ORR performance comparable with Pt/C. • OER at Co 3 O 4 electrocatalyst starts ca. 50 mV earlier than at Co 3 O 4 /SnO 2. • Co 3 O 4 /SnO 2 gave comparable OER current densities to Co 3 O 4. • Co 3 O 4 and Co 3 O 4 /SnO 2 could be promising candidates for metal-air batteries. [ABSTRACT FROM AUTHOR]