General Route to Colloidally Stable, Low-Dispersity Manganese-Based Ternary Spinel Oxide Nanocrystals.

While certain ternary spinel oxides have been well-explored with colloidal nanochemistry, notably the ferrite spinel family, ternary manganese (Mn)-based spinel oxides have not been tamed. A key composition is cobalt (Co)-Mn oxide (CMO) spinel, CoxMn3-xO4, that, despite exemplary performance in multiple electrochemical applications, has few reports in the colloidal literature. Of these reports, most show aggregated and polydisperse products. Here, we describe a synthetic method for small, colloidally stable CMO spinel nanocrystals with tunable composition and low dispersity. By reacting 2+ metal-acetylacetonate (M(acac)2) precursors in an amine solvent under an oxidizing environment, we developed a pathway that avoids the highly reducing conditions of typical colloidal synthesis reactions; these reducing conditions typically push the system toward a monoxide impurity phase. Through surface chemistry studies, we identify organic byproducts and their formation mechanism, enabling us to engineer the surface and obtain colloidally stable nanocrystals with low organic loading. We report a CMO/carbon composite with low organic contents that performs the oxygen reduction reaction (ORR) with a half-wave potential (E1/2) of 0.87 V vs RHE in 1.0 M potassium hydroxide at 1600 rpm, rivaling previous reports for the highest activity of this material in ORR electrocatalysis. We extend the general applicability of this procedure to other Mn-based spinel nanocrystals such as Zn-Mn-O, Fe-Mn-O, Ni-Mn-O, and Cu-Mn-O. Finally, we show the scalability of this method by producing inorganic nanocrystals at the gram scale.

Electrochemical Screening of Metallic Oxygen Reduction Reaction Catalyst Thin Films Using Getter Cosputtering.

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.

Synthesis and characterization of novel ferrocenyl chalcone ammonium and pyridinium salt derivatives.

A novel series of ferrocenyl chalcone ammonium and pyridinium salt derivatives were synthesized in order to improve their solubility in aqueous media. Substituted ferrocenyl chalcones with amines and pyridines were synthesized using the base-catalyzed Claisen-Schmidt reaction, and their corresponding salts were prepared by a nucleophilic quaternization reaction at the nitrogen atom. Most of the synthesized ferrocenyl chalcone salts were soluble in water at room temperature. They were fully characterized by IR, NMR spectroscopy and HRMS spectrometry, and their electrochemistry was studied. The salt derivatives presented chemical reversibility, electrochemical quasi reversibility, and the slope of a plot of Log Ipc (or Ipa) versus Log v were almost 0.5 suggesting that their redox process was controlled by diffusion.