Electronic Synergistic Effects on the Stability and Oxygen Evolution Reaction Efficiency of the Mesoporous LiMn 2- x M x O 4 (M = Mn, Fe, Co, Ni, and Cu) Electrodes.

Stable porous manganese oxide-based electrodes are essential for clean energy generation and storage because of their high natural abundance and health safety. This investigation focuses on mesoporous LiMn _{2- x} M _x O ₄ (where M is Fe, Co, Ni, and Cu and x is 0, 0.1, 0.3, 0.5, and 0.67) electrodes and thin/thick films. The mesoporous electrodes and films are fabricated by coating clear and homogeneous ethanol solutions of the salts (LiNO ₃ , [Mn(OH ₂ ) ₄ ](NO ₃ ) ₂ , and [M(OH ₂ ) _x ](NO ₃ ) ₂ ) and surfactants (P123 and CTAB) and calcining at elevated temperature (denoted as F-LiMn _{2- x} M _x O ₄ , G-LiMn _{2- x} M _x O ₄ , and meso -LiMn _{2- x} M _x O ₄ , respectively). The electrochemical properties, stability, and oxygen evolution reaction (OER) performance of the F/G-LiMn _{2- x} M _x O ₄ electrodes are investigated in alkaline media using a three electrode setup. The F-LiMn _1.33 M _0.67 O ₄ electrodes (where M is Mn, Fe, Co, and Ni) exhibit low Tafel slopes of 60, 43, 44, and 32 mV/dec, respectively. While all the Mn-rich and F-LiMn _{2- x} Fe _x O ₄ electrodes degrade via Mn(VI) disproportionation reaction, the 33% Co electrode shows high stability during the OER. The nickel-based electrodes are stable with as little as 15% Ni and display excellent OER performance over 25% Ni, albeit undergoing a transformation that accumulates Ni(OH) ₂ species on the electrode surface. Copper in the F-LiMn _{2- x} Cu _x O ₄ electrodes is homogeneous at low Cu percentages but forms a CuO phase above 15% Cu, undergoes degradation, and displays a weak OER performance. In short, Co and Ni stabilize the F-LiMn _1.33 Co _0.67 O ₄ and F-LiMn _1.7 Ni _0.3 O ₄ electrodes, which display excellent OER performance.