Nozik discovered that the incorporation of a noble metal in the electrochemical photolysis process, such as platinum and gold, among others, could increase photoactivity, and that an external potential was not required. Wagner and Somorjai (1980) and Sakata and Kawai (1981) delineated hydrogen production on the surface of strontium titanate (SrTiO3) via photogeneration, and the generation of hydrogen and methane from the illumination of and PtO2 in ethanol, respectively. Photocatalysis has not been developed for commercial purposes. Chu et al. (2017) assessed the future of electrochemical photolysis of water, discussing its major challenge of developing a cost-effective, energy-efficient photoelectrochemical (PEC) tandem cell, which would, “mimic natural photosynthesis". Types of photocatalysis Homogeneous photocatalysis In homogeneous photocatalysis, the reactants and the photocatalysts exist in the same phase. A intensively studied theme in homogeneous photocatalysis involves the destruction of ozone: Heterogeneous photocatalysis In heterogeneous catalysis the catalyst is in a different phase from the reactants. Heterogeneous photocatalysis is a discipline which includes a large variety of reactions: mild or total oxidations, dehydrogenation, hydrogen transfer, 18O2–16O2 and deuterium-alkane isotopic exchange, metal deposition, water detoxification, and gaseous pollutant removal. Most heterogeneous photocatalysts are transition metal oxides and semiconductors. Unlike metals, which have a continuum of electronic states, semiconductors possess a void energy region where no energy levels are available to promote recombination of an electron and hole produced by photoactivation in the solid. The void region of energy, which extends from the top of the filled valence band to the bottom of the vacant conduction band, is called the band gap. When a photon with energy equal to or greater than the material's band gap is absorbed by the semiconductor, an electron is excited from the valence band to the conduction band, generating a hole in the valence band. Such a photogenerated electron-hole pair is termed an exciton. The excited electron and hole can recombine and release the energy gained from the excitation of the electron as heat. Such exciton recombination is undesirable and higher levels cost efficieny. Efforts to develop functional photocatalysts often emphasize extending exciton lifetime, improving electron-hole separation using diverse approaches that may rely on structural features such as phase hetero-junctions (e.g. anatase-rutile interfaces), noble-metal nanoparticles, silicon nanowires and substitutional cation doping. The ultimate goal of photocatalyst design is to facilitate reactions of the excited electrons with oxidants to produce reduced products, and/or reactions of the generated holes with reductants to produce