Abstract: A composite electrode, comprising:a solid non-metallic substrate, (such as ceramic, glass, or epoxy resin,)and, bonded directly or indirectly to said substrate,a non-conducting matrix, incorporating particles which are accessible to the electrode surface and contain an insoluble metal salt (e.g. halide) in direct electrical contact with the metal corresponding to said salt, said metal being present either (i) in the form of metallic particles incorporated in a non-conducting matrix zone disposed so that said metal salt-containing particles are located between said metallic particles and said electrode surface, and/or (ii) a solid metallic surface in the form of an intermediate layer between said matrix and said substrate.