Rücker Konstantin K, Taffa Dereje Hailu, Bisen Omeshwari, Risch Marcel, Hayes Darius, Brim Elliot, Richards Ryan M, Harms Corinna, Wark Michael, Lorenz Julian
Institute of Engineering Thermodynamics, German Aerospace Center (DLR), Carl-von-Ossietzky-Str.15, 26129 Oldenburg, Germany.
Institute of Chemistry, Chemical Technology I, Carl von Ossietzky University of Oldenburg, Carl-von-Ossietzky-Str. 9-11, 26129 Oldenburg, Germany.
J Phys Chem C Nanomater Interfaces. 2025 May 10;129(20):9341-9355. doi: 10.1021/acs.jpcc.5c00493. eCollection 2025 May 22.
Understanding dynamic surface reconstruction processes on transition metal oxides for the oxygen evolution reaction (OER) in alkaline electrolytes is crucial to the development of more active catalysts in water electrolysis technologies. Effective strategies in material development for activity enhancement include doping with additional transition metals and surface structuring through controlled exposure of defined surface facets. Here, a microwave-assisted synthesis route was used, that resulted in phase-pure Co- and Mn-doped NiO with various doping levels while maintaining the rock salt crystal structure of the pure, faceted NiO(111) nanosheets. X-ray diffraction and transmission electron microscopy showed an unaltered structure and morphology up to doping levels of 10 mol %. The impact of doping levels between 2 and 10% on the electrochemistry and OER overpotential was studied using the rotating disc electrode technique. A modest overpotential reduction of 34 mV was achieved for 5% Co-doping, being the most active material in the comparison, and an increase in overpotential of 56 mV for 10% Mn-doping, being the least active material, compared to the undoped NiO(111) material. Associated changes in the physical surface area and charges associated with surface redox reactions were aligned with detailed X-ray absorption spectroscopy and X-ray photoelectron spectroscopy analysis before and after electrochemical measurements, which showed different extents of surface reconstruction depending on the dopant and doping level. Thus, transformation of the less active rock salt structure to more active NiOOH functionalities was hampered by a low extent of surface reconstruction, explaining the modest activity enhancement after potentiodynamic cycling for 350 scans. The results demonstrate the effective synthesis of facet-controlled doped NiO-based model catalysts to scrutinize the impact of individual dopants on the electrochemical behavior and, thus the OER electrode activity.
了解碱性电解质中用于析氧反应（OER）的过渡金属氧化物上的动态表面重构过程对于水电解技术中更具活性的催化剂的开发至关重要。提高活性的材料开发有效策略包括用额外的过渡金属进行掺杂以及通过控制特定表面晶面的暴露来进行表面结构化。在此，使用了一种微波辅助合成路线，该路线可得到具有不同掺杂水平的纯相钴和锰掺杂的NiO，同时保持纯的、有晶面的NiO(111)纳米片的岩盐晶体结构。X射线衍射和透射电子显微镜表明，在掺杂水平达到10 mol%时，结构和形态未发生改变。使用旋转圆盘电极技术研究了2%至10%的掺杂水平对电化学和OER过电位的影响。与未掺杂的NiO(111)材料相比，5%的钴掺杂实现了34 mV的适度过电位降低，是比较中最具活性的材料，而10%的锰掺杂使过电位增加了56 mV，是活性最低的材料。与表面氧化还原反应相关的物理表面积和电荷的相关变化与电化学测量前后的详细X射线吸收光谱和X射线光电子能谱分析一致，这表明根据掺杂剂和掺杂水平的不同，表面重构程度也不同。因此，活性较低的岩盐结构向活性更高的NiOOH官能团的转变受到表面重构程度较低的阻碍，这解释了在进行350次扫描电位动态循环后活性的适度提高。结果表明，有效合成了晶面控制的掺杂NiO基模型催化剂，以研究单个掺杂剂对电化学行为以及OER电极活性的影响。
