Influence of fuel ratio on the performance of combustion synthesized bifunctional cobalt oxide catalysts for fuel cell application

Abstract

Solution combustion synthesis was used to prepare cobalt oxide nanoparticles at different fuel ratio (φ = 0.5, 1, and 1.75). The synthesized particles were characterized using XRD, SEM, TEM, FTIR and XPS to study the morphological and structural features. The fuel rich condition provides a reducing atmosphere limiting further oxidation of synthesized nanoparticles but produces more carbon residue on the catalyst surface compared to fuel lean conditions. Increasing the fuel ratio (φ value) from 0.5 to 1.75 increases the crystallite size and lowers the surface area. The electrocatalytic performance studies conducted by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) indicate significant changes in catalytic activities due to variation in synthesis conditions. The LSV results obtained between potential of −1.2 V and 0.75 V shows all the three cobalt oxide catalysts to have bifunctional properties of being active for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), with Co synthesized at lower fuel ratio (φ = 0.5) displaying the highest current density. The onset potential for Co (φ = 0.5) is more positive than Co (φ = 1) and Co (φ = 1.75). The kinetic current density for Co (φ = 0.5) is 6.45 mA cm−2 and decreases with increase in fuel ratio. The OER current starts at ∼0.45 V for all the catalysts showing maximum density for Co (φ = 0.5) and gradually decreasing for catalysts synthesized at higher fuel ratio.