No abstract

A custom-built apparatus for performing rotating disk electrode voltammetry (RDE) using vapor-deposited, epitaxial, thin film samples as rotating electrodes is described. This method allows for quantitative electrochemical characterization using thin film samples, including those deposited on insulating substrates, and allows for very facile exchange of samples. Cyclic voltammetry and RDE voltammetry of iron ferricyanide in aqueous media were explored to examine if the system causes unusual deviations from ideal hydrodynamic voltammetric behavior. The setup was also used to examine the ORR activity of a platinum thin film as a model system for a higher-current reaction, relevant to fuel-cell research. Both studies indicated that the setup did not cause any deviations from anticipated RDE behavior, demonstrating that this is a viable method for performing rotating disk electrode voltammetry of vapor-deposited thin films, with emphasis on those relevant to fuel cell research. The setup was used to investigate/test the ORR and OER activity of a series of A 2 B 2 O 7 pyrochlore samples.

Many material systems have known or predicted functional phases that are metastable at standard temperature and pressure. While substantial advances have been made in the high-throughput and combinatorial synthesis of materials with a range of stoichiometries, investigation of thermal processing remains largely the domain of iterative uniform anneals or static gradients. Here we develop X-ray probed laser anneal mapping (XPLAM), a high throughput technique coupling spatially resolved X-ray diffraction with microsecond to millisecond laser gradient anneals to produce temperature–dwell–transformation (TDT) diagrams of the phase as a function of quench time and temperature. In addition to showing regimes where specific metastable phases form preferentially, TDT diagrams provide insight into the submillisecond kinetics of solid–solid phase transitions. This is a unique tool for mapping reaction pathways for metastable phases. As a first demonstration of XPLAM, we study Bi2O3, which has a rich set of polytypes, including the δ-phase with an exceptionally high oxygen ion conductivity. We demonstrate the first annealing-driven synthesis of room temperature δ-Bi2O3. We expect XPLAM to prove a powerful technique for rapid identification of synthetic routes to metastable phases and to generate the exhaustive data sets required for machine learning-guided exploration of materials processing.

Current commercial fuel cells operate in acidic media where Pt-containing compositions have been shown to be the best oxygen reduction reaction (ORR) electrocatalysts, due to their facile reaction kinetics and long-term stability under operating conditions. However, with the development of alkaline membranes, alkaline fuel cells have become a potentially viable alternative that offers the possibility of using Pt-free (precious metal-free) electrocatalysts. However, the search for better electrocatalysts can be very effort-consuming, if we intend to test every potential bi-or trimetallic combination. In this work, we have explored the application of physical vapor deposition using a custom-built getter cosputtering chamber to prepare catalyst thin films on glassy carbon electrodes, enabling catalyst compositions to be screened in a combinatorial fashion. The activity of combinations containing Au, Cu, Ag, Rh, and Pd as binary metal catalysts, in alkaline media, was studied using rotating disk electrode (RDE) voltammetry with an exchangeable disk electrode holder. Subsequently, we investigated a composition gradient of Pd−Cu, the best performing bimetallic catalyst thin film identified in the initial screening tests. Our results show the viability of using metal getter cosputtering as a rapid and effective tool for preliminary testing of ORR fuel cell electrocatalysts.