A Pt-Au alloy catalyst of varying compositions is prepared by codeposition of Pt and Au nanoparticles onto a carbon support to evaluate its electrocatalytic activity toward an oxygen reduction reaction (ORR) with methanol tolerance in direct methanol fuel cells. The optimum atomic weight ratio of Pt to Au in the carbonsupported Pt-Au alloy (Pt-Au/C) as established by cell polarization, linear-sweep voltammetry (LSV), and cyclic voltammetry (CV) studies is determined to be 2:1. A direct methanol fuel cell (DMFC) comprising a carbon-supported Pt-Au (2:1) alloy as the cathode catalyst delivers a peak power density of 120 mW/cm 2 at 70 °C in contrast to the peak power density value of 80 mW/cm 2 delivered by the DMFC with carbonsupported Pt catalyst operating under identical conditions. Density functional theory (DFT) calculations on a small model cluster reflect electron transfer from Pt to Au within the alloy to be responsible for the synergistic promotion of the oxygen-reduction reaction on a Pt-Au electrode.

Gradual, yet a great leap: electrosynthesized surfactant-stabilized gold atomic clusters (AuACs; Au(n) , 5≤n≤13) electrocatalyze the oxygen reduction reaction (ORR) in acid solution at low overpotentials. Depending on the surfactant concentration, the ORR mechanism gradually transits from a direct four-electron to a two-electron pathway (see picture; SHE=standard hydrogen electrode), which suggests the transformation of atomic clusters into nanoparticles.

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Hydrous ruthenium oxide, which exhibits both protonic and electronic conduction, is incorporated in the cathode electrocatalyst layer of the membrane electrode assembly for polymer electrolyte fuel cells ͑PEFCs͒. The supercapacitive behavior of ruthenium oxide helps realize a fuel cell-supercapacitor hybrid. Platinum ͑Pt͒ nanoparticles are deposited onto carbon-supported hydrous ruthenium oxide and the resulting electrocatalyst is subjected to both physical and electrochemical characterization. Powder X-ray diffraction and transmission electron microscopy reflect the hydrous ruthenium oxide to be amorphous and well-dispersed onto the catalyst. X-ray photoelectron spectroscopy data confirm that the oxidation state of ruthenium in Pt anchored on carbon-supported hydrous ruthenium oxide is Ru 4+ . Electrochemical studies, namely cyclic voltammetry, cell polarization, intrinsic proton conductivity, and impedance measurements, suggest that the proton-conducting nature of hydrous ruthenium oxide helps extend the three-phase boundary in the catalyst layer, which facilitates improvement in performance of the PEFC. The aforesaid PEFC operating with hydrogen fuel and oxygen as oxidant shows a higher power density ͑0.62 W/cm 2 @ 0.6 V͒ in relation to the PEFC comprising carbon-supported Pt electrodes ͑0.4 W/cm 2 @ 0.6 V͒. Potential square-wave voltammetry study corroborates that the supercapacitive behavior of hydrous ruthenium oxide helps ameliorate the pulse-power output of the fuel cell. In the postoil energy economy, hydrogen-based fuel cells are being perceived as a possible energy alternative. Hydrogen-based polymer electrolyte fuel cells ͑PEFCs͒ are most promising as they offer an order of magnitude higher power density than any other fuel cell system. A PEFC is fed with hydrogen, which is oxidized at the anode and oxygen that is reduced at the cathode. The protons released during the oxidation of hydrogen pass through the proton exchange membrane to the cathode. The electrons released during the oxidation of hydrogen travel through the external electric circuit, generating an electric current. Owing to the high degree of irreversibility of the oxygen reduction, even under open-circuit condition, the overpotential of the oxygen electrode in a PEFC happens to be about 0.2 V. This represents a loss of about 20% from the theoretical maximum efficiency for a PEFC. Accordingly, the PEFC cathode electrocatalyst has to possess a high intrinsic activity for the electrochemical reduction of oxygen at the cathode in order to attain the maximum efficiency of the PEFC. 1,2The activity of the cathode catalyst is reportedly improved by design of the tailored catalyst with controlled composition and microstructure. Nevertheless, the high activity of the catalyst itself is necessary, but not a sufficient condition for good fuel cell performance. To ensure the optimum conditions for effective catalyst utilization, an environment must be provided that allows for an adequate supply of reactants as well as good connectivity of the acti...