Taffa Dereje H, Brim Elliot, Rücker Konstantin K, Hayes Darius, Lorenz Julian, Bisen Omeshwari, Risch Marcel, Harms Corinna, Richards Ryan M, Wark Michael
Institute of Chemistry, Chemical Technology I, Carl von Ossietzky University of Oldenburg, Carl-von-Ossietzky-Str. 9-11, 26129 Oldenburg, Germany.
Department of Chemistry, Colorado School of Mines, 1500 Illinois St., Golden, Colorado 80401, United States.
ACS Appl Mater Interfaces. 2024 Nov 13;16(45):62142-62154. doi: 10.1021/acsami.4c14277. Epub 2024 Nov 1.
Earth-abundant transition metal oxides are promising alternatives to precious metal oxides as electrocatalysts for the oxygen evolution reaction (OER) and are intensively investigated for alkaline water electrolysis. OER electrocatalysis, like most other catalytic reactions, is surface-initiated, and the catalyst performance is fundamentally determined by the surface properties. Most transition metal oxide catalysts show OER activities that depend on the predominantly exposed crystal facets/surface structure. Therefore, the design of synthetic strategies to obtain the most active crystal facets is of significant research interest. In this work, rock salt NiO OER catalysts with (111) predominantly exposed facets were synthesized by a solvothermal (ST) method either heated under supercritical or microwave-assisted (MW) conditions. Particular emphasis was placed on the influence of the post annealing temperature on the structural configuration and OER activity to compare their catalytic performances. The as-prepared electrocatalysts are pure α-Ni hydroxides which were converted to rock salt NiO (111) nanosheets with hexagonal pores after heat treatment at different temperatures. The OER activity of the electrodes has been evaluated in 0.1 M KOH using geometric and intrinsic current densities via normalization by the disk area and BET area, respectively. The lowest overpotential at a geometric current density of 10 mA/cm is found for samples pretreated by heating between 400 and 500 °C with a catalyst loading of 115 μg/cm. Despite the very similar nature of the catalysts obtained from the two methods, the ST electrodes show a higher geometric and intrinsic current density for 500 °C pretreatment. The MW electrodes, however, achieve an optimal geometric current density for 400 °C pretreatment, while their intrinsic current density requires pretreatment over 600 °C. Interestingly, pretreated electrodes show consistently higher OER activity as compared to the poorly crystalline/less ordered hydroxide as-prepared electrocatalysts. Thus, our study highlights the importance of the synthesis method and pretreatment at an optimal temperature.
地球上储量丰富的过渡金属氧化物有望成为贵金属氧化物的替代物，用作析氧反应（OER）的电催化剂，并且人们对其在碱性水电解方面进行了深入研究。与大多数其他催化反应一样，OER电催化是表面引发的，催化剂性能从根本上由表面性质决定。大多数过渡金属氧化物催化剂的OER活性取决于主要暴露的晶面/表面结构。因此，设计合成策略以获得最具活性的晶面具有重大的研究意义。在这项工作中，通过溶剂热（ST）法在超临界或微波辅助（MW）条件下加热合成了主要暴露（111）面的岩盐NiO OER催化剂。特别强调了退火后温度对结构构型和OER活性的影响，以比较它们的催化性能。所制备的电催化剂是纯α - 氢氧化镍，在不同温度下热处理后转化为具有六边形孔的岩盐NiO（111）纳米片。通过分别以圆盘面积和BET面积归一化，使用几何电流密度和本征电流密度在0.1 M KOH中评估了电极的OER活性。对于催化剂负载量为115 μg/cm²且在400至500 °C之间加热预处理的样品，在几何电流密度为10 mA/cm²时发现最低过电位。尽管通过两种方法获得的催化剂性质非常相似，但ST电极在500 °C预处理时显示出更高的几何电流密度和本征电流密度。然而，MW电极在400 °C预处理时达到最佳几何电流密度，而其本征电流密度需要在600 °C以上进行预处理。有趣的是，与制备的结晶性差/无序程度较低的氢氧化物电催化剂相比，预处理后的电极始终显示出更高的OER活性。因此，我们的研究突出了合成方法和在最佳温度下进行预处理的重要性。
