Developing Wide Line Solid State NMR as a Novel Analytical Approach to understand Metals in Catalytic Technology for Fuel Cells

斯特恩报告强调，在这一领域必须迫切推动更可持续的能源和引进新技术。燃料电池在未来的能源经济中扮演着关键的角色。然而，许多燃料电池的核心部件之一是昂贵的贵金属电极，因此它们的寿命和高昂的费用往往限制了燃料电池的经济性。由于这些材料的高度非均质性和无序性，理解构成这些催化层的贵金属纳米颗粒的结构通常是困难的。该项目将开发贵金属核的宽线固态核磁共振作为这类纳米颗粒的新表征工具。它将汇集一个长期致力于开发固态核磁共振新材料应用的团队和一个正在开发燃料电池催化剂技术的国际领先工业集团。该项目试图实现《塞恩斯伯里评论》的理念，让核心学术科学基地更直接地与工业互动。传统上，铂催化剂仅用于低温燃料电池，因为它们在三个关键反应中具有足够的活性和稳定性。最近，铂与其他各种金属的合金化在活性和选择性上都有了改善，从而产生了多种特定反应的催化剂。目前，更先进的研究概念集中在纳米核壳材料上，其中铂（或铂合金）外壳沉积在不同的核心（例如钯）上，以获得活性（通过电子修饰）和成本效益。在感兴趣的金属中，铂是关键，因为它是目前大多数活性配方的基础。钯越来越引起人们的兴趣，因为最近的报道表明，钯与贱金属（如铁）合金化可以提高某些反应的活性，而不是铂。此外，它还被广泛用作铂的核心。铑在燃料电池催化方面还没有得到广泛的研究，但它确实有希望作为铂的促进剂用于乙醇的电氧化。此外，铑是许多气相反应的关键催化金属，包括汽车催化中的CO-NOx反应和碳氢化合物燃料重整生成氢。将采用结合传统分析技术（例如XRD， TEM， XPS）以及催化活性测定的表征方法。这些数据将与固态核磁共振提供的新的、可能唯一的信息合并。一个完全多核的方法将被用来检查1H（阐明表面形态和质子迁移率，后者通过弛豫和脉冲场梯度测量），以及13C和27Al的支持材料。然而，这里的工作重点将是直接开发金属的核磁共振。195Pt已经取得了进展，这表明在这种异质系统中确实可以遇到非常宽的谱线，而传统的脉冲方法是不可能的。通过使用场扫描方法，甚至可以记录非常宽的线的精确线形。该项目将采用这一理念，进一步发展195Pt，并承担更具挑战性的任务，即检查103Rh和105Pd。后两个核的固体核磁共振报告极为稀少，这表明了它们的难度。然而，通过使用现有的最先进的核磁共振设备（例如，场扫描，非常高的磁场）和为这些核的静态观察优化的探针的构建，预计可以在观察这些核方面取得重大进展。这将为这些技术上重要的材料提供一种新的分析探索。

The Stern report stresses that that the drive to more sustainable energy and the introduction of new technologies in this area must be urgently pursued. Fuel cells have a key role to play in the future energy economy. However, one of central components in many fuel cells is the precious metal electrodes which are very expensive, such that their longevity and high expense often limit fuel cell economics. Understanding the structure of the precious metal nanoparticles that make up these catalytic layers is often difficult due to the highly heterogeneous, disordered nature of these materials. This project will develop wide line solid state NMR of precious metal nuclei as a new characterisation tool for such nanoparticles. It will bring together a group with a long track record of developing new materials applications of solid state NMR and an internationally-leading industrial group that are developing fuel cell catalyst technologies. The project attempts to fulfil the philosophy of the Sainsbury Review to get the core academic science base interacting more directly with industry. Traditionally, platinum catalysts have been used exclusively for low temperature fuel cells due to their overall adequate activity and stability for three key reactions of interest. More recently, alloying of platinum with various other metals has shown improvements in both activity and selectivity leading to a diverse range of catalysts for specific reactions. Currently, more advanced research concepts are focussed on nano core-shell materials, where a platinum (or platinum alloy) shell is deposited onto a different core (e.g. palladium) to give both activity (through electronic modification) and cost benefits. Of the metals of interest, platinum is key as this is the basis for most current active formulations. Palladium is of increasing interest as recent reports have indicated that alloying palladium with base metals such as iron can increase activity for some reactions to that of platinum. Also, it has been extensively used as a core for platinum. Rhodium has not been extensively investigated for fuel cell catalysis, but it does show promise as a promoter for platinum for the electro-oxidation of ethanol. In addition, rhodium is the key catalytic metal for a large range of gas-phase reactions, including the CO-NOx reaction in automotive catalysis and the reforming of hydrocarbon fuels to give hydrogen. A characterisation approach that combines traditional analysis techniques (e.g. XRD, TEM, XPS) along with determination of the catalytic activity will be employed. This data will be merged with the new and potentially unique information that will be provided by solid state NMR. A fully multinuclear approach will be employed to examine 1H (to elucidate surface speciation and proton mobility, the latter via relaxation and pulsed field gradient measurements), as well as 13C and 27Al of the support materials. However the clear focus of the work here will be developing NMR of the metals directly. There has already been progress made on 195Pt which has shown that in such heterogeneous systems very broad spectral lines indeed can be encountered such that traditional pulsed approaches are not possible. With the use of field-sweep approaches accurate lineshapes of even very broad lines can be recorded. This project will take this philosophy, develop it further for 195Pt and take on the very much more challenging task of examining 103Rh and 105Pd. The reports of solid state NMR from the latter two nuclei are extremely scarce providing an indication of their difficulty. However by the use of the state of the art NMR equipment available (e.g. field sweep, very high magnetic field) and the construction of a probe optimised for the static observation of these nuclei it is anticipated that significant progress can be made in observing such nuclei. This would provide a new analytical probe of these technologically important materials.