Elucidating and Quantifying Parasitic Reactions on Manganese Oxide Electrodes for Acidic Oxygen Evolution Reaction Using In Situ Spectroscopic Techniques

Why It Matters

Understanding the dissolution mechanisms of manganese oxides removes a key barrier to deploying low‑cost, non‑precious catalysts in PEM electrolyzers, potentially lowering hydrogen production costs. The new analytical method offers a rapid diagnostic tool for catalyst optimization.

Key Takeaways

• UV‑vis method detects Mn2+, Mn3+, Mn4+, MnO4− in situ
• Mn oxide electrodes dissolve and undergo disproportionation under acidic OER
• Solid‑phase analysis shows surface reconstruction, redeposition, over‑oxidation
• Findings enable design of more stable non‑precious OER catalysts
• Parasitic reactions quantified from open‑circuit to oxygen evolution potentials

Pulse Analysis

The oxygen evolution reaction (OER) is the rate‑limiting half‑cell in proton‑exchange‑membrane (PEM) water electrolysis, a technology poised to supply green hydrogen at scale. While noble‑metal oxides such as iridium oxide deliver high activity, their scarcity and price drive intense research into earth‑abundant alternatives. Manganese oxides have emerged as a leading candidate because of their low cost and intrinsic catalytic activity in acidic media. However, rapid manganese dissolution and poorly understood side reactions have hampered their commercial viability, creating a critical knowledge gap that this study aims to fill.

The authors present a UV–vis absorption protocol that monitors Mn2+, Mn3+, Mn4+ and MnO4− concentrations in real time during OER operation. By correlating liquid‑phase spectra with ex‑situ and in‑situ electron microscopy, X‑ray photoelectron spectroscopy, and Raman data, they track the electrode’s valence shifts from open‑circuit potential to the oxygen‑evolution regime. The data reveal a three‑stage surface reconstruction: initial disproportionation of Mn3+ to Mn2+ and Mn4+, subsequent redeposition of MnO2, and final over‑oxidation to soluble permanganate. This comprehensive model quantifies the parasitic pathways that erode catalyst performance.

Quantifying these degradation routes equips researchers with a diagnostic framework to engineer more robust manganese‑based OER catalysts. Strategies such as doping, protective coatings, or controlled oxidation states can now be evaluated against a measurable benchmark of Mn dissolution. For the hydrogen economy, extending catalyst lifetime directly reduces the capital cost of PEM electrolyzers, accelerating the transition to low‑carbon fuel production. Moreover, the UV–vis technique is inexpensive and adaptable to other transition‑metal systems, promising broader impact across electrocatalysis research.