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

过去几年，世界能源消费量不断增加，预计未来将有增无减。燃料电池等替代能源的创新和发展，对于帮助世界满足其能源需求，减少对化石燃料及其伴随的温室气体排放的依赖，绝对是至关重要的。然而，在完全实施这些技术之前，必须解决与材料的性能、成本和可靠性相关的重大挑战。 稳定性问题是在寻找铂基ORR催化剂的可行替代品方面普遍缺乏成功的根本原因。可以考虑的材料很少，因为大多数金属在PEMFC阴极的酸性氧化环境中是不稳定的。这种情况在碱性溶液中完全不同，在碱性溶液中，银和金都具有比铂更好的电化学稳定性。因此，在碱性环境中，银基电催化剂和金基电催化剂可能成为铂的有趣替代品，并将被研究。 为此，我们将使用通过在取向的氧化镁衬底上外延生长获得的模型系统。将研究三种不同的取向，即(111)、(110)和(100)。根据最新的密度泛函理论计算，选择了感兴趣的双金属体系。 对于银，这些计算预测了银与铜、镍、钴和铁的合金应该比纯银更强地结合OOH中间体，因此在碱性溶液中应该比纯银表现出更好的ORR特性。 对于Au，同样的计算表明，可以通过将Au与溶质元素混合来改变O物种的吸附热。早期过渡金属元素Sc、Ti、La和Y被认为是最有前途的。 因此，脉冲激光沉积(PLD)将被用来制备具有(111)、(110)和(100)表面取向的外延薄膜，该薄膜由AGM(M=Cu、Ni、Co和Fe)和AuM(M=Sc、Ti、La和Y)双金属化合物组成。将使用PLD沉积技术来实现这一点，因为它允许沉积所有元素，并由于瞬时沉积速度而形成动力学稳定的(亚稳)合金。 该项目有望在碱性溶液中鉴定出具有更好的电催化活性和ORR稳定性的新材料。考虑到银的成本比铂低65倍，寻找新的银基电催化剂材料的前景特别诱人。这可能会缓解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.