Abstract: A combination water electrolyzer and fuel cell for selectively storing and supplying energy while in a substantially fixed position, typically comprising a pan held in a substantially horizontal position, an aqueous alkaline electrolyte (e.g., NaOH) held within the pan at elevated temperature, means communicating with a supply of hydrogen and forming a container for the hydrogen within the pan, a thin nonporous corrosion resistant hydrogen diffusion negative electrode (e.g., PdAg) having a porous support positioned within the pan and having one surface on contact with the electrolyte and an opposite surface communicating with the hydrogen, means communicating with a supply of oxygen and furnishing the oxygen to a region contiguous with the exposed surface of the electrolyte, a thin porous corrosion resistant positive electrode (e.g.