Role of the Morphology and Surface Planes on the Catalytic Activity of Spinel LiMn1.5Ni0.5O4 for Oxygen Evolution Reaction

The electrocatalytic activity of the spinel oxide LiMn1.5Ni0.5O4 with different morphologies (cubic, spherical, octahedral, and truncated octahedral) has been investigated for the oxygen evolution reaction (OER) in alkaline solutions that is of interest for metal−air batteries. The OER activity increases in the order truncated octahedral < cubic < spherical < octahedral, despite a larger surface area (2.9 m2 g−1) for the spherical sample compared to nearly similar surface areas (0.3−0.7 m2 g−1) for the other three samples. The high activity of the octahedral sample is attributed to the regular octahedral shape with low-energy {111} surface planes, whereas the lowest activity of the truncated octahedral sample is attributed to the high-energy {001} surface planes. The octahedral sample also exhibits the lowest Tafel slope of 70 mV dec−1 with the highest durability whereas the truncated octahedral sample exhibits the highest Tafel slope of 120 mV dec−1 with durability similar to the cubic and spherical samples. The study demonstrates that the catalytic activities of oxide catalysts could be tuned and optimized by controlling the surface morphologies/planes via novel synthesis approaches.