Lienau Karla, Triana C A, Reith Lukas, Siol Sebastian, Patzke Greta R
Department of Chemistry, University of Zurich, Zurich, Switzerland.
Empa-Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland.
Front Chem. 2020 Jun 9;8:473. doi: 10.3389/fchem.2020.00473. eCollection 2020.
Water oxidation is the bottleneck reaction for overall water splitting as a direct and promising strategy toward clean fuels. However, the development of robust and affordable heterogeneous water oxidation catalysts remains challenging, especially with respect to the wide parameter space of synthesis and resulting material properties. Oxide catalysts performance in particular has been shown to depend on both synthetic routes and applied catalytic test methods. We here focus on spinel-type CoO as a representative case for an in-depth study of the influence of rather subtle synthetic parameter variations on the catalytic performance. To this end, a series of CoO samples was prepared via time-saving and tunable microwave-hydrothermal synthesis, while systematically varying a single parameter at a time. The resulting spinel-type catalysts were characterized with respect to key materials properties, including crystallinity, oxidation state and surface area using a wide range of analytical methods, such as PXRD, Raman/IR, XAS and XPS spectroscopy. Their water oxidation activity in electrocatalytic and chemical oxidation setups was then compared and correlated with the obtained catalyst properties. Both water oxidation methods displayed related trends concerning favorable synthetic parameters, namely higher activity for lower synthesis temperatures, lower precursor concentrations, addition of hydrogen peroxide and shorter ramping and reaction times, respectively. In addition to the surface area, structural features such as disorder were found to be influential for the water oxidation activity. The results prove that synthetic parameter screening is essential for optimal catalytic performance, given the complexity of the underlying performance-properties relationships.
水氧化是整个水分解反应的瓶颈反应，是一种直接且有前景的制取清洁燃料的策略。然而，开发强大且经济实惠的非均相水氧化催化剂仍然具有挑战性，特别是考虑到合成参数空间广阔以及由此产生的材料特性。尤其是氧化物催化剂的性能已被证明取决于合成路线和应用的催化测试方法。我们在此聚焦于尖晶石型CoO，作为一个代表性案例，深入研究相当细微的合成参数变化对催化性能的影响。为此，通过省时且可调的微波水热合成法制备了一系列CoO样品，同时每次系统地改变一个参数。使用多种分析方法，如PXRD、拉曼/红外光谱、X射线吸收光谱（XAS）和X射线光电子能谱（XPS），对所得的尖晶石型催化剂的关键材料特性进行了表征，包括结晶度、氧化态和表面积。然后比较了它们在电催化和化学氧化装置中的水氧化活性，并将其与获得的催化剂特性相关联。两种水氧化方法在有利的合成参数方面都呈现出相关趋势，即分别在较低合成温度、较低前驱体浓度、添加过氧化氢以及较短的升温时间和反应时间下具有更高的活性。除了表面积外，发现诸如无序等结构特征对水氧化活性也有影响。鉴于潜在的性能-性质关系的复杂性，结果证明合成参数筛选对于获得最佳催化性能至关重要。
