Department of Chemical Engineering, University of South Carolina, 301 South Main Street, Columbia, South Carolina 29208, United States.
Department of Mechanical Engineering, University of South Carolina, 300 South Main Street, Columbia, South Carolina 29208, United States.
ACS Appl Mater Interfaces. 2023 Jun 28;15(25):30139-30151. doi: 10.1021/acsami.3c03256. Epub 2023 Jun 14.
The electrochemical oxidation of H and CO fuels have been investigated on the Ruddlesden-Popper layered perovskite SrLaFeO (SLF) under anodic solid oxide fuel cell conditions using periodic density functional theory and microkinetic modeling techniques. Two distinct FeO-plane-terminated surface models differing in terms of the underlying rock salt layer (SrO or LaO) are used to identify the active site and limiting factors for the electro-oxidation of H, CO, and syngas fuels. Microkinetic modeling predicted an order of magnitude higher turnover frequency for the electro-oxidation of H compared to CO for SLF at short-circuit conditions. The surface model with an underlying SrO layer was found to be more active with respect to H oxidation than the LaO-based surface model. At an operating voltage of less than 0.7 V, surface HO/CO formation was found to be the key rate-limiting step, and the surface HO/CO desorption was the key charge transfer step. In contrast, the bulk oxygen migration process was found to affect the overall rate at high cell voltage conditions above 0.9 V. In the presence of syngas fuel, the overall electrochemical activity is derived mainly from H electro-oxidation and CO is chemically shifted to CO via the reverse water-gas shift reaction. Substitutional doping of a surface Fe atom with Co, Ni, and Mn revealed that the H electro-oxidation activity of FeO-plane terminated anodes with an underlying LaO rock salt layer can be improved with dopant introduction, with Co yielding a three orders of magnitude higher activity relative to the undoped LaO surface model. Constrained ab initio thermodynamic analysis furthermore suggested that the SLF anodes are resistant toward sulfur poisoning both in the presence and absence of dopants. Our findings reflect the role of various elements in controlling the fuel oxidation activity of SLF anodes that could aid the development of new Ruddlesden-Popper phase materials for fuel cell applications.
在阳极固体氧化物燃料电池条件下，使用周期性密度泛函理论和微观动力学建模技术，研究了 H 和 CO 燃料在钙钛矿型层状钙钛矿 SrLaFeO（SLF）上的电化学氧化。使用两种不同的 FeO 面终止表面模型，这些模型在底层岩盐层（SrO 或 LaO）方面有所不同，用于确定 H、CO 和合成气燃料电氧化的活性位点和限制因素。微观动力学模型预测，在短路条件下，与 CO 相比，SLF 电氧化 H 的周转频率高出一个数量级。与基于 LaO 的表面模型相比，具有底层 SrO 层的表面模型在 H 氧化方面更具活性。在工作电压小于 0.7 V 的情况下，表面 HO/CO 形成被发现是关键的速率限制步骤，而表面 HO/CO 脱附是关键的电荷转移步骤。相比之下，在高于 0.9 V 的高电池电压条件下，体相氧迁移过程被发现会影响整体速率。在存在合成气燃料的情况下，整体电化学活性主要来自 H 的电氧化，而 CO 通过逆水气变换反应被化学转化为 CO。在表面 Fe 原子上用 Co、Ni 和 Mn 取代，结果表明，具有底层 LaO 岩盐层的 FeO 面终止阳极的 H 电氧化活性可以通过掺杂来提高，与未掺杂的 LaO 表面模型相比，Co 的活性提高了三个数量级。受约束的从头算热力学分析进一步表明，在存在和不存在掺杂剂的情况下，SLF 阳极对硫中毒具有抵抗力。我们的研究结果反映了各种元素在控制 SLF 阳极燃料氧化活性方面的作用，这有助于开发用于燃料电池的新型钙钛矿相材料。
