Heat-Treated Electrolytic Manganese Dioxide as an Efficient Catalyst for Oxygen Reduction Reaction in Alkaline Electrolyte

Abstract

We developed an oxygen depolarized cathode (ODC) catalyst that can be employed for industrial chlor-alkali electrolysis by improving the oxygen reduction reaction (ORR) activity of commercially available electrolytic manganese dioxide (EMD). The ORR activity of EMD was systematically investigated by rotating disc electrode (RDE) measurements for EMD samples having different particle sizes and heat-treated at different temperatures. We found that the ORR activity of EMD became comparable to commercially available platinized carbon (Pt/C) when EMD with a median diameter of 0.5 μm was heat-treated at 500 °C. From XPS analysis, the EMD heat-treated at 500 °C contains many surface oxygen vacancies that were advantageous for adsorption of oxygen molecules. The obtained EMD sample was assembled into an ODC electrode and its ORR performance was evaluated under chlor-alkali electrolysis conditions (32.5 wt% NaOH, 88 °C). The heat-treated EMD showed an overpotential of ∼0.1 V smaller (at a current density of −1.0 A cm−2) than the benchmark catalyst, i.e., Ag particles. The catalyst we developed is therefore a most promising candidates to replace precious metal catalysts, owing to industrially valuable features such as low cost, simple synthesis method, and high ORR activity.