The Photolytic Production of Hydrogen

Solar energy arrives on the earth at the rate of 170 trillion (1012) kilowatts. It can be converted to useful energy not only along solar thermal or solar electric paths, but also along the solar chemical pathways. From a long-term point of view, this option could be the most important. Its goal is the photochemical decomposition of water to hydrogen and oxygen, after which the hydrogen could be collected and utilized in a hydrogen economy. It may well be that hydrogen can be produced from solar energy by indirect paths—namely, by first producing heat or electricity and then later utilizing these to produce hydrogen—yet the direct decomposition (photolysis) of water is the most immediate way and therefore fundamentally the best one.