Hierarchical Urchin-like Spinel Cu_xCo_3-xO₄ Particles as Oxygen Evolution Reaction Catalysts in Alkaline Medium

In this work, spinel Cu_xCo_3-xO₄ (x = 0.00, 0.50, 1.00, 1.50) was synthesized through a typical ethanol-assisted hydrothermal route. The effect of the incorporation of copper on the resulting morphology, structure, and oxygen evolution reaction (OER) activity of the spinel Co oxides was investigated. In general, Cu-doped samples exhibited improved OER activity associated to the reduction of electrical resistivity of the spinel due to the presence of Cu²⁺ into the lattice. Further, the ionic bonding of OH⁻ with Cu²⁺ is weaker relative to the Co³⁺ ions at the octahedral sites, which could have facilitated OER better. Among the Cu concentration experimented, Cu_0.5Co_2.5O₄ exhibited the best OER catalytic with an onset overpotential and Tafel slope of about 271 mV and 100.4 mV·dec⁻¹, respectively. This is attributed to its better conductivity due to the absence of a resistive secondary CuO phase. (paper)