Abstract: The gas-sensing electrodes prepared according to this invention are specifically designed for cells which operate in a current-limited mode, i.e. at current densities well below 20 mA/cm.sup.2. Such cells are particularly useful to measure or detect a gaseous component of a gaseous environment or stream, provided the gaseous component can be electrochemically oxidized or reduced. In an alkaline, metal-oxygen cell for example, an electrode of this invention can be used as an oxygen cathode. The electrode is prepared by:(a) bringing an exposed face of a self-supporting, electrically-conducting sheet of fibrous or sintered-particle material having a thickness of at least about 30 .mu.m and a flexural strength of at least 2000 kPa into contact with an electrolyte containing ions of a catalytic metal, the electrolyte also being in contact with a counterelectrode,(b) applying a pulsed-D.C.

Abstract: Gas-diffusion electrodes (GDE's) suitable for use with a solid polymer electrolyte (s.p.e.), particularly in s.p.e. fuel cells, which GDE's provide unusually highly efficient use of noble or precious electrocatalytic metals, are obtained by starting with a GDE which is essentially fully fabricated except for electrocatalytic metal treatment and s.p.e. treatment, e.g. a carbon GDE having a gas-permeable hydrophobic face and a particulate carbon-containing catalytic face. This untreated GDE is treated bya. impregnating an s.p.e. solutuion into the catalytic face until the solution penetrates part way into the cross-section of the GDE, especially into the carbon particulate or other support material, but not as far as the hydrophobic, gas permeable face,b. inserting the thus-treated GDE and a counterelectrode into a plating bath containing, for example, M.sup.+, M.sup.++, and/or M.sup.+++ ions, where M is a metal of Group VIII or I-B of the Periodic Table, andc.