Understanding the role of carbon in alkaline oxygen electrocatalysis: A case study on La0.6Sr0.4CoO3-$Δ$/Vulcan carbon composite electrocatalyst

In this work, the role of carbon in alkaline oxygen electrocatalysis was investigated using an oxygen-deficient, perovskite-structured oxide catalyst, La0.6Sr0.4CoO3−$δ$ (LSCO), mixed in different mass ratios with Vulcan carbon (XC-72R, referred to as XC-72) to observe the effect of the LSCO-to-XC-72 ratio (LSCO/XC-72) on the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics. Six different LSCO/XC-72 mass ratios were designed for the study as follows: 1:0 (pure LSCO), 10:1, 7:1, 5:1, 2:1 and 1:1. A thin-film oxygen electrode consisting of the LSCO/XC-72 catalysts was characterized in 0.1 M KOH solution using cyclic voltammetry (CV), rotating disk electrode (RDE) based linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). A physics-based, generalized electrochemical model was used to establish the charge-transfer mechanism and to obtain the electrode kinetic transfer coefficients and exchange current densities for the electrochemical reactions considered. The results show that the oxygen electrocatalysis process depends quite heavily on the carbon content in the catalyst, and there appears to be a synergistic effect between the perovskite-oxide and the XC-72, with a transition from the two-step, 2e− pathway to the direct 4e− transfer pathway as carbon content increases.