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.

本研究针对金属-空气电池领域具有重要应用价值的碱性体系析氧反应（oxygen evolution reaction, OER），系统探究了不同形貌（立方、球形、八面体与截角八面体）的尖晶石氧化物（spinel oxide）LiMn₁.₅Ni₀.₅O₄的电催化活性。尽管球形样品的比表面积达2.9 m²·g⁻¹，远高于其余三种样品的0.3~0.7 m²·g⁻¹，但OER活性仍按截角八面体＜立方＜球形＜八面体的顺序递增。八面体样品的高催化活性可归因于其规整的八面体形貌与低能{111}晶面，而截角八面体样品活性最低则源于其暴露的高能{001}晶面。性能测试结果显示，八面体样品同时具备最低的塔菲尔斜率（Tafel slope，70 mV·dec⁻¹）与最优的循环稳定性；反之，截角八面体样品的塔菲尔斜率最高（120 mV·dec⁻¹），其稳定性则与立方、球形样品相近。本研究证实，通过新型合成策略调控氧化物催化剂的表面形貌与晶面，可有效调节并优化其催化活性。