TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Material: The electrocatalyst particles are composite electrocatalyst aggregates comprising a support phase and an active species phase, or a platinum metal phase dispersed on the support phase. The aggregates are spherical.Preferred Method: Heating comprises heating the suspended droplets in a mixed-flow spray-dryer to not more than 400, preferably not more than 300degreesC for not more than 600, preferably not more than 100 seconds.Preferred Dimension: The electrocatalyst particles have a volume average particle size of not more than 30, preferably not more than 10, more preferably 1-10 mum; average internal pore size of not more than 15 nm; and an open porosity of at least40%.The support phase comprises primary carbon particles having an average primary particle size of 10-1000, preferably 10-100 nm. The volume average size of the aggregates is not more than 100, preferably not more than 20, more preferably 1-50 mum. The electrocatalyst aggregates are dispersed in an electrocatalyst layer having an average thickness of not more than 50, preferably not more than 25 mum.Preferred Parameter: at least5, preferably 20 vol.% of the electrocatalyst layer comprises the spherical electrocatalyst particles. at least60 vol.% porosity is derived from porosity between aggregates. The electrocatalyst layer has a supported active species loading of not more than 0.2, preferably not more than 0.1, more preferably not more than 0.4 mg/cm2; has a DELTA E value of not more than 50, preferably not more than 250 mV at 200, preferably 1000 mA/cm2, when measured at 50degreesC, and atmospheric pressure using a feed gas of pure hydrogen to the anode at a constant flow rate and with external humidification. The platinum loading on the particles is not more than 40, preferably not more than 60 wt.%.Preferred Component: The liquid vehicle comprises catalyst particles. The electrocatalyst comprises manganese oxide active species phase dispersed on primary carbon support particles. The liquid vehicle comprises a solvent and a binder.Preferred Condition: The liquid vehicle is heated to at least200degreesC.Preferred Property: The cell voltage of the membrane electrode assembly is at least0.6, preferably at least0.7, more preferably at least0.5 V at a constant current density of at least600, preferably at least150, more preferably at least1000 mA/cm2 at 50degreesC, and atmospheric pressure, using a feed gas of pure air to the cathode and pure hydrogen to the anode at a constant flow rate and with external humidification. The reference voltage decreases in average by not more than 7.5 mu-V/hour when the membrane electrode assembly is run for a continuous period of 4000 hours at 50degreesC, and atmospheric pressure with a feed gas of pure air to the cathode, and a feed gas of pure hydrogen to the anode at a constant flow rate and with external humidification. The membrane electrode assembly uses a feed gas of pure air to the cathode (2.2 stoichiometry) and pure hydrogen to the anode (1.2 stoichiometry), with constant flow rates corresponding to current density of 1 A/cm2 and with 100% external humidification of the gases. The support structure has a porosity of at least40%.    TECHNOLOGY FOCUS - POLYMERS - Preferred Component: The electrocatalyst comprise a polymer phase intimately mixed within the structure of the aggregates. The polymer phase comprises a proton conductive polymer; a hydrophobic polymer; a hydrophilic polymer; a fluorocarbon polymer; and a perfluorohydrocarbon polymer.Preferred Parameter: The electrocatalyst layer comprises 20-40 vol.% electrocatalyst; 20-40 vol.% proton conducting polymer; and at least30 vol.% porosity.