Mechanistic Parameters of Electrocatalytic Water Oxidation on LiMn₂ O₄ in Comparison to Natural Photosynthesis

Targeted improvement of the low efficiency of water oxidation during the oxygen evolution reaction (OER) is severely hindered by insufficient knowledge of the electrocatalytic mechanism on heterogeneous surfaces. We chose LiMn₂ O₄ as a model system for mechanistic investigations as it shares the cubane structure with the active site of photosystem II and the valence of Mn^3.5+ with the dark-stable S1 state in the mechanism of natural photosynthesis. The investigated LiMn₂ O₄ nanoparticles are electrochemically stable in NaOH electrolytes and show respectable activity in any of the main metrics. At low overpotential, the key mechanistic parameters of Tafel slope, Nernst slope, and reaction order have constant values on the RHE scale of 62(1) mV dec^-1 , 1(1) mV pH^-1 , -0.04(2), respectively. These values are interpreted in the context of the well-studied mechanism of natural photosynthesis. The uncovered difference in the reaction sequence is important for the design of efficient bio-inspired electrocatalysts.