A thin film ceramic proton conducting electrolyte assembly (10) is provided having a includes a nanoporous, copper supporting substrate (11), a temporary substrate pore filler material (12), and a ceramic electrolyte layer (13) positioned upon the substrate (11). The ceramic electrolyte layer may be made of a yttrium doped strontium zirconate. To produce the electrolyte the substrate pores (14) are filled with the pore filler material to provide a smooth surface upon which the electrolyte layer is deposited. The filler material is then removed from the pores and the substrate and electrolyte layer are annealed.