and earth abundant for the widespread adoption of PEC water splitting to be feasible. While the listed requirements can be applied generally, photoanodes and photocathodes have slightly different needs. A good photocathode will have early onset of the oxygen evolution reaction (low overpotential), a large photocurrent at saturation, and rapid growth of photocurrent upon onset. Good photoanodes, on the other hand, will have early onset of the hydrogen evolution reaction in addition to high current and rapid photocurrent growth. To maximize current, anode and cathode materials need to be matched together; the best anode for one cathode material may not be the best for another. In 1967, Akira Fujishima discovered the Honda-Fujishima effect, (the photocatalytic properties of titanium dioxide). and other metal oxides are still most prominent catalysts for efficiency reasons. Including and , this kind of semiconducting titanates, the conduction band has mainly titanium 3d character and the valence band oxygen 2p character. The bands are separated by a wide band gap of at least 3 eV, so that these materials absorb only UV radiation. Change of the microstructure has also been investigated to further improve the performance. In 2002, Guerra (Nanoptek Corporation) discovered that high localized strain could be induced in semiconductor films formed on micro to nano-structured templates, and that this strain shifted the bandgap of the semiconductor, in the case of titanium dioxide, into the visible blue. It was further found (Thulin and Guerra, 2008) that the strain also favorably shifted the band-edges to overlay the hydrogen evolution potential, and further still that the strain improved hole mobility, for lower charge recombination rate and high quantum efficiency. Chandekar developed a low-cost scalable manufacturing process to produce both the nano-structured template and the strained titanium dioxide coating. Other morphological investigations include nanowire arrays or porous nanocrystalline photoelectrochemical cells. GaN GaN is another option, because metal nitrides usually have a narrow band gap that could encompass almost the entire solar spectrum. GaN has a narrower band gap than but is still large enough to allow water splitting to occur at the surface. GaN nanowires exhibited better performance than GaN thin films, because they have a larger surface area and have a high single crystallinity which allows longer electron-hole pair lifetimes. Meanwhile, other non-oxide semiconductors such as GaAs, , and are used as n-type electrode, due to their stability in chemical and electrochemical steps in the photocorrosion reactions. Silicon