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