How can electromagnetic energy (photons) be efficiently converted to chemical energy? For example, can water be efficiently split to hydrogen and oxygen using solar energy?
Chemical energy, the energy of chemical bonds, is electromagnetic energy.
Water can be split into hydrogen and oxygen using solar energy, for instance-cf. https://www.alternative-energy-news.info/splitting-water-into-hydrogen-and-oxygen/
How can electromagnetic energy (photons) be efficiently converted to chemical energy?
This is very tricky question. Electromagnetic energy? = photon?
convert to chemical energy?
1st any chemical energy has mass.. but electromagnetic or photon has no mass.
One of the most unscientific question you asking. I hope I am wrong and you are right. My opinion your question is worst than E=mc^2, which it not science . But hey best to you!