A photocatalyst, as the name suggests, speeds up a photochemical reaction, a reaction that operates in the presence of (normally) ultraviolet light. They do this by creating electron hole pairs according to band theory which then produce free radicals (molecules with an unbonded electron) which are very reactive and allow for a different chemical pathway with a lower energy requirement and so speed up the reaction. One of the most common photochemical reactions is water splitting to produce hydrogen and oxygen. Using electrolysis to split water is very energy inefficient and using a pure reaction is abhorrently slow so a catalyst is used very often.
Recently a new photocatalyst, C12N7H3, has been designed. Its crystal structure gives it a controllable surface area and the fact it is organic, containing no metal, is a big advantage. Metal catalysts skim the chance of heavy metal poisoning and the limited manipulation of the active sites is always a problem. The full electronic structure and alignment states of C12N7H3 has already been calculated and there are four different methods of suggested application for the catalyst already laid out. The use of hydrogen as a possible future fuel means that any improvement in its production, no matter how small, has the possibility of creating a massive difference in the future.