Peak performance: Electrochemical experiments show that the oxygen reduction reaction (ORR) on platinum monolayers supported on various transition metals exhibits a volcano‐type behavior (see graph). Calculations reveal that bond‐breaking occurs more easily as bond‐making becomes harder, and why the Pd‐supported Pt monolayer (PtML/Pd(111)) has higher ORR activity than pure Pt(111).

We describe a new class of electrocatalysts for the O 2 reduction, and H 2 and methanol oxidation reactions, consisting of a monolayer of Pt deposited on a metal or alloy carbon-supported nanoparticles. These electrocatalysts show up to a 20-fold increase in Pt mass activity compared with conventional all-Pt electrocatalysts. The origin of their increased activity was identified through a combination of experimental methods, employing electrochemical and surface science techniques, X-ray absorption spectroscopy, and density functional theory calculations. The long-term tests in fuel cells demonstrated excellent stability of the anode and good stability of the cathode electrocatalysts. We also describe the stabilization of Pt electrocatalysts against dissolution under potential cycling regimes effected by a submonolayer of Au clusters deposited on Pt surfaces. These new electrocatalysts promise to alleviate some of the major problems of existing fuel cell technology.

Ethanol, with its high energy density, likely production from renewable sources and ease of storage and transportation, is almost the ideal combustible for fuel cells wherein its chemical energy can be converted directly into electrical energy. However, commercialization of direct ethanol fuel cells has been impeded by ethanol's slow, inefficient oxidation even at the best electrocatalysts. We synthesized a ternary PtRhSnO(2)/C electrocatalyst by depositing platinum and rhodium atoms on carbon-supported tin dioxide nanoparticles that is capable of oxidizing ethanol with high efficiency and holds great promise for resolving the impediments to developing practical direct ethanol fuel cells. This electrocatalyst effectively splits the C-C bond in ethanol at room temperature in acid solutions, facilitating its oxidation at low potentials to CO(2), which has not been achieved with existing catalysts. Our experiments and density functional theory calculations indicate that the electrocatalyst's activity is due to the specific property of each of its constituents, induced by their interactions. These findings help explain the high activity of Pt-Ru for methanol oxidation and the lack of it for ethanol oxidation, and point to the way to accomplishing the C-C bond splitting in other catalytic processes.

The kinetics of oxygen reduction was studied in acid solutions on Pt monolayers deposited on a Pd(111) surface and on carbon-supported Pd nanoparticles using the rotating disk-ring electrode technique. These electrocatalysts were prepared by a new method for depositing Pt monolayers involving the galvanic displacement by Pt of an underpotentially deposited Cu monolayer on a Pd substrate and characterized by scanning tunneling and transmission electron microscopies. The kinetics of O 2 reduction shows a significant enhancement at Pt monolayers on Pd(111) and Pd nanoparticle surfaces in comparison with the reaction on Pt(111) and Pt nanoparticles. The four-electron reduction, with a first-charge transfer-rate determining step, is operative on both surfaces. The observed increase in the catalytic activity of Pt monolayer surfaces compared with Pt bulk and nanoparticle electrodes may reflect decreased formation of PtOH. An enhanced atomic scale surface roughness and low coordination of some atoms may contribute to the observed activity. The results illustrate that placing a Pt monolayer on a suitable metal nanoparticle substrate is an attractive way of designing better O 2 reduction electrocatalysts. Also, by using this method the Pt content is reduced to very low levels. The Pt mass-specific activity of the Pt/Pd/C electrode is 5-8 times higher than that of the Pt/C electrocatalyst. The noble metal (Pt + Pd) mass-specific activity is two times higher than that of Pt/C.

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-surfacearea carbon. Plotting the correlation between the experimentally determined activities of these three types of electrocatalysts with the calculated metal d-band center energies, d , revealed a volcano-type dependence. In all cases, the electronic properties of the metal electrocatalysts, represented by the d value, were used for elucidating the metal-dependent catalytic activities, and establishing their electronic propertiessthe 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.