In 2013 a cell with 2 nanometers of nickel on a silicon electrode, paired with a stainless steel electrode, immersed in an aqueous electrolyte of potassium borate and lithium borate operated for 80 hours without noticeable corrosion, versus 8 hours for titanium dioxide. In the process, about 150 ml of hydrogen gas was generated, representing the storage of about 2 kilojoules of energy. Structured materials Structuring of absorbing materials has both positive and negative affects on cell performance. Structuring allows for light absorption and carrier collection to occur in different places, which loosens the requirements for pure materials and helps with catalysis. This allows for the use of non-precious and oxide catalysts that may be stable in more oxidizing conditions. However, these devices have lower open-circuit potentials which may contribute to lower performance. Hematite Researchers have extensively investigated the use of hematite (α-Fe2O3) in PEC water-splitting devices due to its low cost, ability to be n-type doped, and band gap (2.2eV). However, performance is plagued by poor conductivity and crystal anisotropy. Some researchers have enhanced catalytic activity by forming a layer of co-catalysts on the surface. Co-catalysts include cobalt-phosphate and iridium oxide, which is known to be a highly active catalyst for the oxygen evolution reaction. Tungsten oxide Tungsten(VI) oxide (WO3), which exhibits several different polymorphs at various temperatures, is of interest due to its high conductivity but has a relatively wide, indirect band gap (~2.7 eV) which means it cannot absorb most of the solar spectrum. Though many attempts have been made to increase absorption, they result in poor conductivity and thus WO3 does not appear to be a viable material for PEC water splitting. Bismuth vanadate With a narrower, direct band gap (2.4 eV) and proper band alignment with water oxidation potential, the monoclinic form of has garnered interest from researchers. Over time, it has been shown that V-rich and compact films are associated with higher photocurrent, or higher performance. Bismuth Vanadate has also been studied for solar H2 generation from seawater, which is much more difficult due to the presence of contaminating ions and a more harsh corrosive environment. Oxidation form Photoelectrochemical oxidation (PECO) is the process by which light enables a semiconductor to promote a catalytic oxidation reaction. While a photoelectrochemical cell typically involves both a semiconductor (electrode) and a metal (counter-electrode), at sufficiently small scales, pure semiconductor particles can behave as microscopic photoelectrochemical cells. PECO