Solution combustion synthesis of porous Co3O4 nanoparticles as oxygen evolution reaction (OER) electrocatalysts in alkaline medium

Abstract

In this work, porous spinel Co3O4 nanoparticles were synthesized through solution combustion. Initially, the effect of calcination on the morphology, phase composition, and electrocatalytic behavior towards oxygen evolution reaction (OER) of the synthesized oxides was investigated. As the as-synthesized powder prepared at stoichiometric conditions (fuel-to-oxidizer ratio, ϕ = 1) and pH = 3 was calcined at 300 and 500 °C, the products became more compact and dense. XRD results showed that a subsequent heat treatment is required to produce a single phase-oxide, as the as-synthesized sample was a mixture of spinel Co3O4 and monoclinic CoO. The mixed phase oxide exhibited excellent electrocatalytic performance in 1 M KOH with onset overpotential and Tafel slope values as low as 361 mV and 87.54 mV dec−1, respectively. Its enhanced properties compared to the calcined samples could be ascribed to its high specific surface area, lower crystallinity, and excellent porosity. Following such findings, uncalcined samples were produced with different ϕ, and pH values. At ϕ = 1 and pH = 1, the sample registered an onset overpotential and Tafel slope of 353 mV and 74.93 mV dec−1, respectively. The sample produced at ϕ = 0.5 and pH = 3, exhibited the best OER catalytic activity with an onset overpotential and Tafel slope as low as 334 mV and 61. 77 mV dec−1. Catalytic activity enhancement is possibly due to better control of phase composition and morphology achieved by employing fuel-lean (ϕ < 1) and acidic conditions.