Stability evaluation of earth‐abundant metal‐based polyoxometalate electrocatalysts for oxygen evolution reaction towards industrial PEM electrolysis at high current densities

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We investigated the cobalt polyoxometalate catalyst Ba8[Co9(H2O)6(OH)3(HPO4)2(PW9O34)3] in oxygen evolution reaction for large‐scale water electrolysis. The catalyst was characterized, yielding BET surfaces (8.37 m2/g), crystal water content (8.38%, 44 H2O), elemental analyses and single crystal structures (space group P1̅, a = 19.901(4) Å, b = 21.177(4) Å, c = 24.036(5) Å, α = 92.689(7)°, β = 108.73(7)°, γ = 117.137(6)°, Co9Na16O196.05P5W27, V = 8310(3) Å2 with z = 2; R2final = 0.001). The catalyst was integrated in an industrially applicable membrane electrode assembly and electrochemically characterized. Polarization studies revealed catalyst dissolution in situ, visible as a current density peak (32.2 mA/cm2, 2.2 V) with subsequent collapse (<5 mA/cm2). Galvanostatic experiments showed voltage increase from 2.5 to > 10 V at 10 mA/cm2 tracing back to acid‐mediated decomposition of the anionic POM oxide framework. We deduced insufficient thermodynamic as well as kinetic stability for industrial requirements in PEM water electrolysis.