In Vitro Photosynthetic Hydrogenase System- The photosynthetic apparatus of higher plants, i.e., chloroplasts, and the hydrogenase produced by H₂ producing bacteria have been combined in an in vitro system to produce H₂ from water using solar energy. The photysystem I generates H⁺, e^- and O₂ from H₂O, while hydrogenase combines e^- and H⁺ to yield H₂

This system functions and produces H₂, but is unstable due partly to the sensitivity of hydrogenase to the O₂ produced by photosystem component of the arrangement. Further research is expected to resolve the instability problems; if this does happen, this H₂ production system may develop into an economically attractive process.