NOVELTY - A carbon aerogel supported metal catalyst impregnated with solid electrolyte composite (C1), comprises a carbon aerogel support; metal catalyst particles and solid electrolyte (greater than 5 wt.% of the total weight of the composite). The metal particles have an average particle size of less than or equal to2.5 nm.    USE - As catalyst layer in fuel cell membrane electrode assembly (claimed) also useful as catalysts for chemical reactions, e.g. hydrogenation or dehydrogenation, oxidation, isomerization, reforming, hydrocracking and polymerization.    ADVANTAGE - The carbon aerogel supported catalyst and electrolyte composite have exceptionally high surface area and exceptionally high catalyst utilization. The carbon aerogel support has a surface area of at least 600 m2/g carbon, measured by BET N2 physiorption, and pore volume of at least 0.6 ml/g. The fuel cell membrane electrode assembly (MEA) produces open circuit voltage higher than 950 mv using less than 0.15 mg platinum metal per centimeter squared.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a fuel cell membrane assembly comprising a catalyst layer including the composite (C1);    (2) a method (M2) for preparing a supported metal catalyst, in which the resultant average metallic particle size is less than or equal to 2.5 nm and the weight of metallic particles is greater than or equal to30 wt.% of the catalyst, involving contacting a metal precursor with a support (S1) in a supercritical fluid; reducing the metal precursor by thermal reduction under inert atmosphere below 220degreesC or by hydrogen or hydrogen-inert gas mixture reduction below 150degreesC to form metallic particles;    (3) a process (M1) for preparing an electrode catalytic layer material involving contacting a carbon aerogel supported catalyst with a solid electrolyte solution; and applying an electrical field; and    (4) a process for preparing electrode catalytic layer material for an electrochemical device comprising contacting a carbon supported catalyst with a solution of an electrolyte to be used to conduct ions through a membrane; applying electrical fields to the carbon supported catalyst and the electrolyte containing solution to form a catalyst and electrolyte composite; and drying the catalyst and electrolyte composite.