Electrolysis is a process of detaching or dissociating bonded elements and compounds by passing through them an electric current. Water electrolysis decomposes H2O into hydrogen and oxygen gas. Care must be taken in choosing the correct electrolytes, nominally substances that contain free ions and hence behave as an electrically conductive medium.
Electrolytes dissolve and dissociate into cations (positive ions, +) and anions (negative ions, −) that carry the current. Such processes can occur in an electrolysis cell, or electrolyzer, which consists of two electrodes, cathode and anode, where reduction and oxidation reactions simultaneously take place forming H2 (at the cathode) and O2 (at the anode). The fundamental problem in hydrogen production by water electrolysis is that today the electricity used to drive the process is primarily generated by the burning of fossil fuels.
Photoelectrolysis describes electrolysis by the direct use of light; that is to say, the conversion of light into electrical current and then the transformation of a chemical entity (H2O, H2S, etc.) into useful chemical energy (such as H2) using that current. A photoelectrochemical cell is used to carry out the various photoelectrolytic reactions, being comprised of a semiconductor device that absorbs solar energy and generates the necessary voltage to split water molecules.
Photoelectrolysis integrates solar energy collection and water electrolysis into a single photoelectrode, and is considered the most efficient renewable method of hydrogen production. Our interest in hydrogen stems from it being an energy source that, like fossil fuels, are energy dense and can be readily transported and stored, but unlike fossil fuels is not of finite supply and its combustion does not result in pollution nor the release of climate altering gases.
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