Advancements in AEM Anode Catalysts: Calcium Manganese Oxide as a High Performing Bioinspired Electrocatalyst for Oxygen Evolution Reaction Applications
Authors: Lenhart Brian , Wagner Lindsay , Mckinney Samuel , Ostraat Michele 
Published: December 2024

Anion exchange membrane water electrolyzers (AEMWE) have garnered significant attention over the past decade among researchers worldwide due to their economical electrolyzer components, including bipolar plates, flow fields, electrocatalysts, and membrane materials. They represent a cost-effective alternative to high-performing yet expensive proton exchange membrane water electrolyzers (PEMWE). The allure of AEMWE lies in their affordable cell hardware and components, albeit at the expense of somewhat reduced durability and overall performance compared to PEMWE systems. While AEMWE anodes may not match the activity levels of noble metal catalysts, their abundance and cost-effectiveness render them compelling options. Interest in this domain revolves around utilizing earth-abundant metal oxides, binary and ternary metal oxides featuring transition metals like iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn), and other readily available materials boasting various oxidation states and coordination configurations. Among these, manganese-based oxides such as MnO2 and its derivatives have been extensively explored for their oxygen evolution reaction (OER) activity. Intriguingly, the complexation of manganese with calcium (Ca) to yield CaMnOx electrodes mirrors the active site complexes found in natural metalloenzymes involved in facilitating OER processes, such as those seen in photosynthetic enzymes like photosystem II. These bioinspired electrocatalysts, mimicking nature's design, hold immense promise for integration into AEMWE setups as cost-effective, durable, and efficient OER catalysts [1], [2], [3], [4]. In this study, we investigate CaxMnyOxz electrocatalysts with varying atomic ratios through comprehensive performance and durability evaluations via Rotating Disk Electrode (RDE), Gas Diffusion Electrode (GDE) half-cell, and Membrane Electrode Assembly (MEA) testing. In-house MEA stability testing out to 25 hours at 1 A/cm2 demonstrated steady state voltages of 1.87 V and 1.90 V for CaMn3Ox and CaMn4Ox, respectively. Additionally, polarization curves at 0 h and 20 h reveal an improvement in performance from 1.9 V at 1 A/cm2 down to 1.8 A/cm2 for both CaxMnyOxz catalysts, suggesting an activation of the CaxMnyOxz with use. Our findings reveal that these CaMnOx-based anodes perform comparably to benchmarked commercially available NiFeOx counterparts for AEMWE applications, underscoring their potential as viable alternatives in the pursuit of sustainable hydrogen production.
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