The Bionic Leaf is an artificial leaf that interfaces a triple-junction Si wafer with amorphous silicon photovoltaic with hydrogen- and oxygen-evolving catalysts made from a ternary alloy, nickel-molybdenum-zinc (NiMoZn) and a cobalt–phosphate cluster (Co-OEC). The Co-OEC is able to operate in natural water at room temperature. Accordingly, the Bionic Leaf can be immersed in water and when held up to sunlight, it can effect direct solar energy conversion via water-splitting.
The Bionic Leaf, by virtue of the Co-OEC, also exhibits self-assembling and self-healing properties. The Co-OEC self-assembles upon oxidation of an earth metal ion from 2+ to 3+. It also self-heals upon application of a potential, wherein the cluster reforms due to equilibrium between aqueous cobalt and phosphate.
The Bionic Leaf can be used in artificial photosynthetic systems. One such system is a hybrid water-splitting-biosynthetic system that can operate at low driving voltages. The catalyst system of the Bionic Leaf is used in conjunction with bacterium Ralstonia eutropha. The bacterium is grown in contact with the catalysts and then consumes the produced H from the water-splitting reaction. After consumption, the bacterium synthesizes biomass and fuels or chemical products from low CO concentration in the presence of O. The usage of the bacterium requires a biocompatible catalyst system that is not toxic to the bacterium and that lowers the overpotential for water splitting. The original catalyst used, the nickel-molybdenum-zinc (NiMoZn) alloy, poisoned the microbes by destroying the bacteria's DNA. Accordingly, this hybrid system uses a cobalt-phosphorus (Co-P) alloy cathode that is resistant to reactive oxygen species. This in return leaves no excess metal and does not form oxygen radicals, leaving the microbes and DNA unharmed. This alloy drives the hydrogen evolution reaction while a cobalt-phosphate (CoP) anode drives the oxygen evolution reaction. This new catalyst can run up to 16 days at a time when compared to the nickel-molybdenum-zinc (NiMoZn) alloy.