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

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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.