Platinum substituted Cobalt(II, III) Oxide: Interplay of tetrahedral Co(II) sites towards electrochemical oxygen evolution activity

Substitution of ionic platinum is carried out in Co<inf>3</inf>O<inf>4</inf> host synthesized by solution combustion strategy. These Pt substituted Co<inf>3</inf>O<inf>4</inf> spinels characterized by XRD show pure crystalline phase of Co<inf>3</inf>O<inf>4</inf> without any separated peaks related to Pt/PtO<inf>x</inf>. Electrochemical OER activities of these spinels are investigated by cyclic voltammetry, linear sweep voltammetry and chronoamperometry in neutral, alkaline and neutral buffer electrolytes. LSV studies on 1% Pt substituted Co<inf>3</inf>O<inf>4</inf> exhibit a low overpotential (η) of 455 mV at 20 mA cm⁻² in KOH, as compared to PBS medium. Tafel slope value of 117 mV dec⁻¹ in KOH represents one electron EC mechanism. The detailed XPS studies indicate that Pt doping increases the tetrahedral Co²⁺ sites of Co<inf>3</inf>O<inf>4</inf>. XPS studies before and after OER also infers that the mixed valence of Co in the host (Co<inf>3</inf>O<inf>4</inf>) undergoes redox (Co²⁺/Co³⁺) changes with simultaneous reduction in Pt dopant from Pt⁴⁺ to Pt²⁺ influencing the OER activity.