Chasing the holy grail in water splitting

Kazuhiko Maeda (from Tokyo Institute of Technology) explains well in his recent review that a Z-scheme photocatalyst system can make dreams come true: producing hydrogen and oxygen gases from water by sunlight. Combining a H₂ evolution photocatalyst with an O₂ evolving one is known for sometime as the key for ultimate artificial photosynthesis. Although hopeful developments exist (as also elaborated in this 15-page-long-and-strong article), I don't feel much optimistic about this photocatalytic water splitting in general. A cold-fusion-like fate is certainly not out of sight. We have to be careful.