While artificial photosynthesis works in the lab, it's not ready for mass consumption. Replicating what happens naturally in green plants is not a simple task.
Efficiency is crucial in energy production. Plants took billions of years to develop the photosynthesis process that works efficiently for them; replicating that in a synthetic system takes a lot of trial and error.
The manganese that acts as a catalyst in plants doesn't work as well in a man-made setup, mostly because manganese is somewhat unstable. It doesn't last particularly long, and it won't dissolve in water, making a manganese-based system somewhat inefficient and impractical. The other big obstacle is that the molecular geometry in plants is extraordinarily complex and exact -- most man-made setups can't replicate that level of intricacy.
Stability is an issue in many potential photosynthesis systems. Organic catalysts often degrade, or they trigger additional reactions that can damage the workings of the cell. Inorganic metal-oxide catalysts are a good possibility, but they have to work fast enough to make efficient use of the photons pouring into the system. That type of catalytic speed is hard to come by. And some metal oxides that have the speed are lacking in another area -- abundance.
In the current state-of-the-art dye-sensitized cells, the problem is not the catalyst; instead, it's the electrolyte solution that absorbs the protons from the split water molecules. It's an essential part of the cell, but it's made of volatile solvents that can erode other components in the system.
Advances in the last few years are starting to address these issues. Cobalt oxide is a stable, fast and abundant metal oxide. Researchers in dye-sensitized cells have come up with a non-solvent-based solution to replace the corrosive stuff.
Research in artificial photosynthesis is picking up steam, but it won't be leaving the lab any time soon. It'll be at least 10 years before this type of system is a reality [source: Boyd]. And that's a pretty hopeful estimate. Some people aren't sure it'll ever happen. Still, who can resist hoping for artificial plants that behave like the real thing?