Inception of Co₃O₄ as Microstructural Support to Promote Alkaline Oxygen Evolution Reaction for Co_0.85Se/Co₉Se₈...

Developing electrocatalysts with abundant active sites is a substantial challenge to reduce the overpotential requirement for the alkaline oxygen evolution reaction (OER). In this work, we have aimed to improve the catalytic activity of cobalt selenides by growing them over the self-supported Co₃O₄ microrods. Initially, Co₃O₄ microrods were synthesized through annealing of an as-prepared cobalt oxalate precursor. The subsequent selenization of Co₃O₄ resulted in the formation of a grainy rodlike Co₃O₄/Co_0.85Se/Co₉Se₈ network. The structural and morphological analysis reveals the presence of Co₃O₄ even after the selenization treatment where the cobalt selenide nanograins are randomly covered over the Co₃O₄ support. The resultant electrode shows superior electrocatalytic activity toward OER in alkaline medium by delivering a benchmark current density of 10 mA/cm²_geo at an overpotential of 330 mV. As a comparison, we have developed Co_0.85Se/Co₉Se₈ under similar conditions and evaluated its OER activity. This material consumes an overpotential of 360 mV to deliver the benchmark current density, which signifies the role of the Co₃O₄ support to improve the electrocatalytic activity of Co_0.85Se/Co₉Se₈. Despite having a low TOF value for Co₃O₄/Co_0.85Se/Co₉Se₈ (0.0076 s^-1) compared to Co_0.85Se/Co₉Se₈ (0.0102 s^-1), the improved catalytic activity of Co₃O₄/Co_0.85Se/Co₉Se₈ is attributed to the presence of a higher number of active sites rather than the improved per site activity. This is further supported from the C_dl (double layer capacitance) measurements where Co₃O₄/Co_0.85Se/Co₉Se₈ and Co_0.85Se/Co₉Se₈ tender C_dl values of about 8.19 and 1.08 mF/cm², respectively, after electrochemical precondition. As-prepared Co₃O₄/Co_0.85Se/Co₉Se₈ also manifests rapid kinetics (low Tafel slope ∼ 91 mV/dec), long-term stability, low charge-transfer resistance, and 82% Faradaic efficiency for alkaline electrocatalysis (pH = 14). Furthermore, the proton reaction order (ρRHE) is found to be 0.65, indicating a proton decoupled electron transfer (PDET) mechanism for alkaline OER. Thus, the Co₃O₄ support helps in the exposure of more catalytic sites of Co_0.85Se/Co₉Se₈ to deliver the improved catalytic activities in alkaline medium.