Mn-doped Co₃O₄ for acid, neutral and alkaline electrocatalytic oxygen evolution reaction

This work reports the application of Mn-doped Co₃O₄ oxides in the electrocatalytic oxygen evolution reaction (OER). The materials were characterized by structural, morphological, and electrochemical techniques. The oxides with higher Co : Mn molar ratio presented a lower electron transfer resistance, and consequently the most promising OER activities. Pure Co₃O₄ shows an overpotential at j = 10 mA cm⁻² of 761, 490, and 240 mV, at pH 1, 7, and 14, respectively, and a high TOF of 1.01 × 10⁻¹ s⁻¹ at pH 14. Tafel slopes around 120 mV dec⁻¹ at acidic pH and around 60 mV dec⁻¹ at alkaline pH indicate different OER mechanisms. High stability for Co₃O₄ was achieved for up to 15 h in all pHs, and no change in the structure and morphology after the electrocatalysis was observed. The reported excellent OER activity of the Mn-Co oxides in a wide pH range is important to broaden the practical applicability in different electrolyte solutions.