TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Material: The support is carbon black, graphitized carbon, graphite, activated carbon, alumina, silica, silica-alumina, titania, zirconia, calcium carbonate, barium sulfate, a zeolite, and/or interstitial clay.    TECHNOLOGY FOCUS - METALLURGY - Preferred Component: The atomically thin layer of platinum atoms is an atomic submonolayer, monolayer, bilayer, and/or trilayer of platinum atoms. The particle composite comprises a palladium alloy core coated with an atomically thin layer of platinum atoms. The palladium alloy core comprises a homogeneous or heterogeneous combination of palladium and an alloying metal. The heterogeneous combination comprises an inner core of alloying metal coated with a layer of palladium. The particle composite comprises metal-bonding ligands or surfactants on the surface layer of zerovalent platinum. The palladium or palladium alloy core is coated with an atomic submonolayer of zerovalent platinum atoms. The atomic submonolayer of zerovalent platinum atoms is in combination with a submonolayer of one or a combination of metals other than platinum, providing a platinum-metal alloy monolayer. The metal alloy core comprises a combination of greater than or equal to 2 metals consisting palladium, rhenium, gold, rhodium, iridium, ruthenium, and osmium. It comprises a homogeneous or heterogeneous alloy of rhenium-rhodium, rhenium-ruthenium, rhenium-gold, or rhenium-iridium. It comprises one or more second row and/or third row transition metals in combination with one or more first row transition metals consisting zerovalent nickel, cobalt, or iron; and zerovalent or charged gold atoms in combination with one or a combination of first row transition metals. It is at least partially homogeneous or at least partially heterogeneous. It comprises an inner subcore comprising one or a combination of first row transition metals, the inner subcore at least partially encapsulated by an outer shell comprising one or a combination of zerovalent or charged second row and/or third row transition metal atoms. The outer shell is atomically thin. It is an atomic submonolayer, monolayer, bilayer, and/or trilayer, of the one or combination of second row and/or third row transition metals. It comprises an inner subcore of one or a combination of first row transition metals consisting zerovalent iron, cobalt, or nickel, the inner subcore at least partially encapsulated by an outer shell comprising one or a combination of zerovalent or charged second row and/or third row transition metals consisting gold, rhodium, iridium, ruthenium, osmium, or rhenium. The platinum-metal alloy monolayer is a platinum-iridium alloy monolayer, platinum-ruthenium alloy monolayer, platinum-osmium alloy monolayer, platinum-rhenium alloy monolayer, or platinum-gold alloy monolayer. Preferred Material: The alloying metal is a transition metal, which is a first row transition metal. The transition metal is iron, cobalt, and/or nickel. The metal other than platinum is a transition metal, which is iridium, ruthenium, osmium, or rhenium. The platinum-metal alloy monolayer is of formula iridium platinum (Ir0.2Pt0.8), ruthenium platinum (Ru0.2Pt0.8), osmium platinum (Os0.2Pt0.8), or rhenium platinum (Re0.2Pt0.8). Preferred Parameter: The particle composite has a size of approximately 3-100, preferably 5 nm.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Component: The electrically conductive support is carbon-based. It is carbon black, graphitized carbon, graphite, or activated carbon. The fuel source is hydrogen gas, which is generated from reformed methanol, reformed methane, or reformed gasoline. It is an alcohol. EXAMPLE - The Pt-coated Pd nanoparticle composite was prepared by depositing atomically thin platinum layers on Pd nanoparticles by redox displacement by platinum of an adlayer of an underpotentially deposited (upd) metal (i.e. copper) on a Pd nanoparticle substrate. To prepare an electrode with Pd nanoparticles, a dispersion of Pd nanoparticles on Vulcan XC-72(RTM: Not defined) carbon substrate (Pd/C) was made by sonicating the Pd/C nanoparticles in water for 5-10 minutes to make a uniform suspension. Then, 5 mul of this suspension was placed on a glassy carbon disk (GC) electrode and dried in air. The GC electrode holding the Pd/C nanoparticles was then placed in a 50 mM CuSO4/0.10 M H2SO4 solution to electrodeposit copper. After electrodeposition of copper monolayer, the electrode was rinsed to remove copper ions from the electrode. The electrode was then placed in an aqueous solution containing 1.0 mM K2PtCl4 in 50 mM H2SO4 in a nitrogen atmosphere. After a 1-2 minute immersion to completely replace copper by platinum, the electrode was rinsed again.