Understanding the activity and stability of electrode materials targeted for clean energy applications through diagnostic impedance measurements

该研究计划的重点是针对电化学能源系统的先进材料的基础研究。特别是金属/金属合金纳米颗粒，先进的碳材料以及金属纳米颗粒与这些碳的组合。这些材料是许多电化学能源技术的核心，包括燃料电池，电解槽和电化学/超级电容器。这些技术有可能在能源领域得到更广泛的应用，前提是可以提高材料的性能成本比，并提高其耐用性。除了材料本身的改进之外，还需要改进诊断工具，以便于评估电极健康状态的多个指标。该提案的重点是研究和增强新的电极材料，并改进电化学阻抗谱（EIS）测量作为一种诊断工具。我们最近开发了一种基于EIS的诊断方法，可以清楚地阐明电极退化发生的模式。EIS曲线的特定变化发生在降解时，其是特定催化剂层降解过程的特征，包括碳载体和离聚物的降解。此外，我们已经修改了传输线的EIS模型，使双层电容（Cdl）可以从法拉第赝电容（CF）起源于Hupd的Pt。此外，我们已经能够表明，源自Hupd的CF的大小与Pt表面积成比例，产生电位依赖常数，使得能够从EIS测量中准确测量多晶Pt电极的电化学活性表面积。这套基于EIS的工具具有巨大的潜力，可以研究电极的稳定性以及典型Pt/C电极以外的应用中的表面过程。因此，我们正在进行的研究将集中在新型电极材料上，采用EIS来阐明电极表面如何随着时间的推移而变化，并量化金属和碳基的活性表面物种，以及这如何影响活性。较长期的目标包括研究结构与相关性质之间的关系，如导电性、电化学活性表面积、催化活性、容量和性能。此外，我们将寻求扩展我们的EIS方法，以便它可以普遍应用于结合到电极表面的电化学可寻址氧化还原物质的定量。

This research program focuses on fundamental studies of advanced materials targeted for electrochemical energy systems. Specifically metal/metal-alloy nanoparticles, advanced carbon materials as well as combinations of metals nanoparticles with these carbons. Such materials are at the heart of numerous electrochemical energy technologies, including fuel cells, electrolyzers and electrochemical/super capacitors. These technologies have the potential to be more widely deployed in the energy landscape provided that improvements can be made in the performance-to-cost ratio of the materials, and also in their durability. In addition to improvements in the materials themselves, improvements are needed in diagnostic tools that can readily assess multiple indicators of the electrode state-of-health.******This proposal is focused on the study and enhancement of new electrode materials and the refinement of electrochemical impedance spectroscopy (EIS) measurements as a go-to diagnostic tool. We have recently developed an EIS-based diagnostic methods that can clearly elucidate the mode of electrode degradation occurring. Specific changes in the EIS profiles occur upon degradation that are characteristic of specific catalyst layer degradation processes, including the degradation of the carbon support and the ionomer. Furthermore, we have modified the transmission line EIS model so that double-layer capacitance (Cdl) can be separated from faradaic pseudo-capacitance (CF) originating from Hupd on Pt. Moreover, we have been able to show that magnitude of CF originating from Hupd is proportional to the Pt surface area, yielding potential-dependent constants that enable accurate measurements of the electrochemically active surface area of a poly-crystalline Pt electrodes from EIS measurements.******Together this suite of EIS-based tools has enormous potential to study both the stability of an electrode and also surface processes in applications beyond typical Pt/C electrodes. Thus, our ongoing studies will focus on novel electrode materials, employing EIS to elucidate how the electrode surface is changing over time and also to quantify active surface species, both metallic and carbon-based, and how this impacts activity. Longer-term objectives include an examination of the relationships between structure and relevant properties such as conductivity, electrochemically active surface area, catalytic activity, capacity and performance. Furthermore, we will seek to extend our EIS methodology so that it can be applied universally in the quantification of electrochemically addressable redox species bound to an electrode surface.**