Recent advances in solid polymer electrolyte fuel cell technology

With methods used to advance solid polymer electrolyte fuel cell technology, we are close to obtaining the goal of 1 A/cm/sup 2/ at 0.7. Higher power densities have been reported (2 A/cm/sup 2/ at 0.5 V) but only with high catalyst loading electrodes (2 mg/cm/sup 2/ and 4 mg/cm/sup 2/ at anode and cathode, respectively) and using a Dow membrane with a better conductivity and water retention characteristics. Work is in progress to ascertain performances of cells with Dow membrane impregnated electrodes and Dow membrane electrolytes. 5 refs., 6 figs

Role of Transition Metals on TM/Mo2C Composites: Hydrogen Evolution Activity in Mildly Acidic and Alkaline Media

Modification of electronic and chemical properties of a material by the introduction of another element into its lattice is one of the most common methods for designing new catalysts for different applications. In this work the effect of modifying molybdenum carbide with transition metals (Fe, Co, Ni, Cu), TM-Mo2C composites, upon the catalytic activity toward hydrogen evolution reaction (HER) in mild acidic and alkaline media has been studied. Catalysts were prepared by carbothermal reduction of molybdenum and TM oxides precursors and were characterized by different physicochemical techniques. Results evidenced a strong pH effect on the catalytic performance of TM-Mo2C, while, at pH = 5, inclusion of TM into the Mo2C lattice has a deleterious effect on the HER activity and, at pH = 9, a promoting effect was observed, highlighting the importance of considering specific operation conditions during the catalyst design process. Analysis of in situ near-edge X-ray adsorption data reveals a decrease on the oxidation state and average bond ionicity of dopant metal upon a pH increase, shedding light of the different effects of TMs on the resulting HER activity in acidic and alkaline media. Finally, stability tests demonstrated no deterioration on catalysts' performance after 8 h of continuous cycling within the HER working range, confirming the suitability of Mo2C materials as promising HER catalysts

Catalytic activity - d-band center correlation for the O2 reduction reaction on platinum in alkaline solutions

We determined, by the rotating disk electrode technique, the kinetics of the oxygen-reduction reaction (ORR) on the surfaces of single crystals of Au(111), Ag(111), Pd(111), Rh(111), Ir(111), and Ru(0001), on Pt monolayers deposited on their surfaces, and also on nanoparticles of these metals dispersed on high-surface-area carbon. Plotting the correlation between the experimentally determined activities of these three types of electrocatalysts with the calculated metal d-band center energies, εd, revealed a volcano-type dependence. In all cases, the electronic properties of the metal electrocatalysts, represented by the εd value, were used for elucidating the metal-dependent catalytic activities, and establishing their electronic properties - the ORR kinetics relationship. Pt(111), Pt/C, and Pt/Pd(111) were found to top their corresponding volcano plots. Pd in alkaline solutions showed particularly high activity, suggesting it may offer potential replacement for Pt in fuel cells. © 2007 American Chemical Society

Pt monolayer electrocatalysts for O 2 reduction: PdCo/C substrate-induced activity in alkaline media

We measured the activity of electrocatalysts, comprising Pt monolayers deposited on PdCo/C substrates with several Pd/Co atomic ratios, in the oxygen reduction reaction in alkaline solutions. The PdCo/C substrates have a core-shell structure wherein the Pd atoms are segregated at the particle's surface. The electrochemical measurements were carried out using an ultrathin film rotating disk-ring electrode. Electrocatalytic activity for the O 2 reduction evaluated from the Tafel plots or mass activities was higher for Pt monolayers on PdCo/C compared to Pt/C for all atomic Pd/Co ratios we used. We ascribed the enhanced activity of these Pt monolayers to a lowering of the bond strength of oxygenated intermediates on Pt atoms facilitated by changes in the 5d-band reactivity of Pt. Density functional theory calculations also revealed a decline in the strength of PtOH adsorption due to electronic interaction between the Pt and Pd atoms. We demonstrated that very active O 2 reduction electrocatalysts can be devised containing only a monolayer Pt and a very small amount of Pd alloyed with Co in the substrate. © 2007 Springer-Verlag