Electrode arrays containing 91 combinations of Pt-Sn-M (M = Fe, Ni, Pd, and Ru) were prepared by borohydride reduction of aqueous metal salts on carbon paper, and screened by fluorescence assay for activity as ethanol eletrooxidation catalysts. Catalysts that showed high activity for this reaction were identified as being Pt( 80)Sn( 10)Fe(10), Pt( 80)Sn( 10)Ni(10), Pt( 70)Sn( 20)Pd( 10), and Pt( 70)Sn( 10)Ru(20) (numbers in parenthesis indicate atomic percent). These were significantly more active than Pt or PtSn catalysts, also present in the electrode arrays. These 4 compositions were synthesized as nanoparticles and characterized physically and electrochemically. X-ray diffraction showed a Pt face-centered cubic (fcc) structure with an average crystallite

A novel, highly stable, non-carbon support system for the oxygen reduction reaction (ORR) has been discovered in the form of nano-structured (NbxTi1-x)Ns (x = 0.25 and 0.5). Template-free, solid-solid separation synthetic approaches have been used for preparing these materials. The (NbxTi1-x)N materials have high specific surface area and better electronic conductivity than carbon-based supports.

Materials with long-term durability and electrical conductivity at low pH (<2) and high potentials (∼1.4 V vs RHE) are of great interest as catalyst supports in proton exchange membrane (PEM) fuel cells. We have evaluated Ta−Ti−Al nitrides for this purpose. Combinatorial sputter-deposition of Ta−Ti−Al nitride thin films allowed the composition of these films to be varied spatially over a substrate at ∼1 atomic %/mm, enabling the investigation of the conductivity and microstructure of these materials over a wide range of compositions. Conductive probe atomic force microscopy (cp-AFM) is shown to facilitate high-throughput screening of electrical conductivity as a function of composition. Local, tip-induced oxidation of the film indicated that films annealed in the presence of oxygen were most resistant to oxidation-induced losses of conductivity. Ti-rich compositions exhibited conductivities similar to carbon black and best retained their conductivity after tipinduced oxidation. Small amounts of Ti (∼20 atomic %) were sufficient to impart desired conductivities to compositions rich in Ta and Al, which without Ti exhibited insulating behavior. Electron energy-loss spectroscopy (EELS) imaging revealed the formation of a <2 nm oxide layer at the surface of the nitride films, which is expected to make these materials more durable. Remarkably, high conductivities were observed in the presence of this oxide layer. Segregation of elements was observed at sub-10-nm length scales, yet mapping the lattice constant of the film with X-ray diffraction showed that the majority phase is a wellmixed alloy with a lattice constant that varies smoothly over the entire range of compositions. The rock-salt structure was observed at all compositions except those with high levels of Al.

No abstract

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.