NASA is currently studying the use of hydrogen as aviation fuel. Slush hydrogen has a lower temperature and a higher density than liquid hydrogen. Most of the hydrogen produced today is consumed on site, such as at an oil refinery, and is not sold on the market. When hydrogen is sold on the market, the cost of liquefying the hydrogen and transporting it to the user must be added to the production cost. Photoelectrochemistry is the study of semiconductors in contact with a liquid solution.
Light shining on a semiconductor can initiate a chemical reaction with species in solution.
With respect to solar energy, the interest in photoelectrochemistry stems from the fact that this system can split water into hydrogen and oxygen. The hydrogen can then be used in a fuel cell to generate nonpolluting electricity or to fuel a vehicle. Hydrogen and oxygen will burn to form water if in an appropriate mixture. This is true of most chemical compounds. Every major automaker is developing fuel cell vehicles, although some are focusing on other fuels with onboard reforming instead of hydrogen.