Hydrogen Production by the Electrolysis of Water: The Kinetic and Thermodynamic Framework

The electrical energy efficiency of commercial water electrolyzers i normally limited by internal energy losses; heat generated at economic urrent density levels exceeds the heat required to maintain the temperature ofthe electrolyte, and cooling must be used. The energy losses reflect he effects of ohmic resistance and of the electrode overvoltages. Develop-ment of activated electrode systems and of improved electrode geometries promises to reduce these losses to the point where efficiency will be limited instead by the requirement that sufficient heat be generated internally to maintain the electrolyte temperature. The limitation on electrical energy efficiency then becomes thermodynamic. This paper eviews the maj or thermodynamic and kinetic considerations which impact design of industrial water electrolyzers. Options indica-ted for development ofadvanced technology are considered. These are then related to the approaches being taken in major worldwide programs which are working to reduce the cost of hydrogen production from water and electricity. The process of hydrogen production by the elec-trolysis of water is well~established industr ia l ly (1). I t has found its economic niche in a broad range of applications and locations where high purity is re-quired, or where merchant hydrogen a d hydrogen