Oxygen reduction reaction activity on Pt{111} surface alloys.

PtM overlayers (where M=Fe, Co or Ni) supported on Pt{111} are prepared via thermal annealing in either a nitrogen/water or hydrogen ambient of dilute aqueous droplets containing M(Z+) cations directly attached to the electrode. Two different PtM phases are detected depending on the nature of the post-annealing cooling environment. The first of these consists of small (<20 nm), closely packed microcrystals comprised of a central metallic core and a shell (several monolayers thick) of mixed metal oxides/hydroxides. The second type of PtM phase is prepared by cooling in a stream of hydrogen gas. Although this second phase also consists of numerous microcrystals covering the Pt{111} electrode surface, these are both flatter than before and moreover are entirely metallic in character. A positive shift in the onset of PtM oxide formation correlates with increased activity towards the oxygen reduction reaction (ORR), which we ascribe to the greater availability of platinum metallic sites under ORR conditions.

Specific adsorption of perchlorate anions on Pt{hkl} single crystal electrodes.

The voltammetry of Pt{111}, Pt{100}, Pt{110} and Pt{311} single crystal electrodes as a function of perchloric acid concentration (0.05-2.00 M) has been studied in order to test the assertion made in recent reports by Watanabe et al. that perchlorate anions specifically adsorb on polycrystalline platinum. Such an assertion would have significant ramifications for our understanding of electrocatalytic processes at platinum surfaces since perchlorate anions at low pH have classically been assumed not to specifically adsorb. For Pt{111}, it is found that OHad and electrochemical oxide states are both perturbed significantly as perchloric acid concentration is increased. We suggest that this is due to specific adsorption of perchlorate anions competing with OHad for adsorption sites. The hydrogen underpotential deposition (H UPD) region of Pt{111} however remains unchanged although evidence for perchlorate anion decomposition to chloride on Pt{111} is reported. In contrast, for Pt{100} no variation in the onset of electrochemical oxide formation is found nor any shift in the potential of the OHad state which normally results from the action of specifically adsorbing anions. This suggests that perchlorate anions are non-specifically adsorbed on this plane although strong changes in all H UPD states are observed as perchloric acid concentration is increased. This manifests itself as a redistribution of charge from the H UPD state situated at more positive potential to the one at more negative potential. For Pt{110} and Pt{311}, marginal changes in the onset of electrochemical oxide formation are recorded, associated with specific adsorption of perchlorate. Specific adsorption of perchlorate anions on Pt{111} is deleterious to electrocatalytic activity in relation to the oxygen reduction reaction (ORR) as measured using a rotating disc electrode (RDE) in a hanging meniscus configuration. This study supports previous work suggesting that a large component of the ORR activity on platinum is governed by simple site blocking by specifically adsorbed anions and/or electrosorbed oxide.

Ion Speciation and Transport Properties of LiTFSI in 1,3-Dioxolane Solutions: A Case Study for Li-S Battery Applications.

Lithium-sulfur battery is considered to be one of the main candidates for "post-lithium-ion" battery generation because of its high theoretical specific capacity and inherently low cost. The role of electrolyte is particularly important in this system, and remarkable battery performances have been reported by tuning the amount of salt in the electrolyte. To further understand the reasons for such improvements, we chose the lithium bis(trifluoromethanesulfonyl)imide in 1,3-dioxolane electrolyte as a model salt-solvent system for a systematic study of conductivity and viscosity over a wide range of concentration from 10-5 up to 5 m. The experimental results, discussed and interpreted with reference to the theory of electrolyte conductance, lead to the conclusion that triple ion formation is responsible for the highest molal conductivity values before reaching the maximum at 1.25 m. At higher concentrations, the molal conductivity drops quickly because of a rapid increase in viscosity and the salt-solvent system can be treated as a diluted form of molten salt.

Accelerated Discovery of Thermoelectric Materials: Combinatorial Facility and High-Throughput Measurement of Thermoelectric Power Factor.

A series of processes have been developed to facilitate the rapid discovery of new promising thermoelectric alloys. A novel combinatorial facility where elements are wire-fed and laser-melted was designed and constructed. Different sample compositions can be achieved by feeding different element wires at specific rates. The composition of all the samples prepared was tested by energy dispersive X-ray spectroscopy (EDS). Then, their thermoelectric properties (power factor) at room temperature were screened in a specially designed new high-throughput setup. After the screening, the thermoelectric properties can be mapped with the possibility of identifying compositional trends. As a proof-of-concept, a promising thermoelectric ternary system, Al-Fe-Ti, has been identified, demonstrating the capability of this accelerated approach.