Multi-metallic electrocatalysts with engineered nanoscale features and well-defined crystallographic orientation

过去几年，世界能源消耗不断增加，预计未来还会有增无减。燃料电池等替代能源的创新和开发，对于帮助世界满足其能源需求，减少其对化石燃料的依赖及其伴随的温室气体排放至关重要。然而，在全面实施这些技术之前，必须解决与材料的性能、成本和可靠性相关的重大挑战。 稳定性问题是在确定铂基ORR催化剂的可行替代品方面普遍缺乏成功的根本原因。可以考虑非常少的材料，因为大多数金属在PEMFC阴极的酸性氧化环境中不稳定。这种情况在碱性溶液中完全不同，Ag和Au在碱性溶液中具有比Pt更上级的电化学稳定性。因此，Ag和Au基电催化剂可能构成Pt在碱性环境中的ORR的有趣的替代品，并将进行研究。 要做到这一点，我们将使用模型系统通过取向MgO衬底上的外延生长。将研究三种不同的取向，即（111）、（110）和（100）。的感兴趣的dielectric系统已被选定的最新的密度泛函理论计算的基础上。 在Ag的情况下，这些计算预测Ag与Cu、Ni、Co和Fe的合金应比纯Ag更强地结合OOH中间体，因此应在碱性溶液中比纯Ag表现出更好的ORR特性。 在Au的情况下，相同的计算表明，通过将Au与溶质元素混合，可以进行O物质的吸附热的改变。前过渡金属元素Sc、Ti、La和Y被认为是最有前途的。 因此，脉冲激光沉积（PLD）将用于制备具有（111）、（110）和（100）表面取向的外延膜，其包括AgM（M = Cu、Ni、Co和Fe）和AuM（M = Sc、Ti、La和Y）的双金属化合物。PLD沉积技术将用于实现这一点，因为它允许所有元素的沉积，沿着由于瞬时沉积速率而形成动力学稳定（亚稳）合金。 该项目预计将导致识别具有改善的电催化活性和碱性溶液中ORR稳定性的新材料。考虑到Ag的成本比Pt低65倍，识别新的Ag基电催化剂材料的前景特别吸引人。这可能会减轻碱性燃料电池最终商业化的技术障碍之一。

The world energy consumption has continuously increased over the past years and is expected to grow unabated in the future. Innovation in and development of alternative energy sources, such as fuel cells, are absolutely fundamental to helping the world meet its energy needs, and reducing its dependency on fossil fuels with its concomitant emissions of greenhouse gases. However, significant challenges associated with the performance, cost, and reliability of materials must be addressed prior to fully implementing these technologies. The issue of stability is the fundamental reason for the general lack of success in identifying viable alternatives to Pt-based ORR catalysts. Very few materials may be considered, as the majority of metals are unstable in the acidic oxidative environment of a PEMFC cathode. This situation is radically different in alkaline solutions, and both Ag and Au possess superior electrochemical stability than Pt in base. Accordingly, Ag- and Au-based electrocatalysts may constitute interesting alternatives to Pt for the ORR in alkaline environments, and will be studied. To do so, we will use model systems obtained through epitaxial growth on oriented MgO substrates. Three different orientations will be investigated, namely (111), (110) and (100). The bimetallic systems of interest have been selected on the basis of the most recent density-functional theory calculations. In the case of Ag, these calculations predict that alloys of Ag with Cu, Ni, Co and Fe should bind the OOH intermediate more strongly than pure Ag, and therefore should exhibit better ORR characteristics in alkaline solutions than pure Ag. In the case of Au, the same calculations indicate that modification of the heat of adsorption of the O-species may be performed by mixing Au with solute elements. The early transition metal elements Sc, Ti, La and Y have been identified as the most promising. Accordingly, Pulsed Laser Deposition (PLD) will be used to prepare epitaxial films with (111), (110) and (100) surface orientations comprised of AgM (with M = Cu, Ni, Co and Fe) and AuM (with M = Sc, Ti, La and Y) bimetallic compounds. The PLD deposition technique will be used to achieve this, as it allows for the deposition of all elements, along with the formation of kinetically stable (metastable) alloys, due to the instantaneous deposition rate. This project is expected to lead to the identification of new materials with improved electrocatalytic activity and stability for the ORR in alkaline solutions. The prospect of identifying new Ag-based electrocatalyst materials is particularly appealing, considering the cost of Ag is sixty-five times lower than that of Pt. This may alleviate one of the technological barriers to the eventual commercialization of alkaline fuel cells.