Fuel cells 50 Catalysts 30 Methanol 22 Proton exchange membrane fuel cells (PEMFC) 22 Electrodes 16 Mesoporous materials 16 Platinum 16 Carbon 14 Carbon dioxide 14 Catalyst activity 14 Electrolytic reduction 14 Oxidation 14 Carbon monoxide 12 Copper 12 Hydrogen production 12 Bioelectric Energy Sources 10 Cathodes 10 Ethanol 10 Hydrogen 10 Mesoporous carbon 10 PEM fuel cell 10 Catalyst supports 8 Cerium 8 Hydrogen purification 8 Membrane electrode assemblies 8 Polyelectrolytes 8 Polymers 8 Preferential oxidation of CO 8 bioenergy 8 Anodes 6