In a photocatalysis system for degrading toxic compounds to constituent components, an improved photoreactor system optimizes reaction rates on the surface of a wide bandgap semiconductor electrode material. The semiconductor material has a first surface exposed to light having a higher energy than the bandgap and a second surface exposed to the toxic compound. An electrical conductor contacts the semiconductor electrode material in a geometry effective to produce an electric field within the semiconductor material. A controlled voltage source is connected to the electrical conductor for applying a voltage bias effective to produce the electric field. A closed circuit current sensor or an open circuit voltage sensor is connected to the electrical conductor and outputs a current or voltage signal, respectively, that is indicative of an excess electrical charge in the semiconductor material. A processor monitors the current or the voltage signal and controls the voltage source to minimize the excess electrical charge.
