Electrochemical gas evolution, eg chlorine, hydrogen and oxygen evolution today are technically performed applying catalytic coatings which use intrinsically highly active catalysts of properly adjusted micromorphologies. Gas diffusion electrodes in fuel cells achieve highest utilization of precious metal catalysts by proper design of the porous electrode and the size of the catalyst particles. For highly porous catalytic coatings of gas evolving and gas consuming electrodes, eg Raney-nickel coated hydrogen evolving cathodes as well as for gas diffusion electrodes, slow diffusive mass transfer of the dissolved gases in the electrolyte limits the utilization of the nanoporous catalyst particles, the number of merit for the porous structures being the electrochemical Thiele modulus. Decreasing the particle size, ie matching the size/thickness of porous catalyst particles/coatings to their intrinsic catalytic activity and the applied current density allows to diminish the Thiele modulus and to increase catalyst utilization to the highest possible degree.