How can electromagnetic energy (photons) be efficiently converted to chemical energy? For instance, can water be efficiently split to hydrogen and oxygen using solar energy? As we are running out of non-renewable resources is there any way for us to use the solar energy so efficiently to generate power?
You can certainly turn electromagnetic energy into chemical energy, but the key is 'efficiently.'
A photo-voltaic cell can be used to split water into Hydrogen and Oxygen. The Hydrogen can be burned or used in a fuel cell.
But the key is how efficient is 'efficient.'
Each step will lose energy, but if solar is the input, there is a huge supply. If a solar powered system were continually operating, and we had many of these systems, a huge amount of Hydrogen gas can be generated. Even considering the costs of delivering to where it is needed (which can be paid with the product itself) there is a huge and realistically limitless supply.
That being said, there is much 'waste' which hampers a calculated efficiency, but once established a system that relies on water for a raw material is relatively efficient because there is very little required for raw material acquisition.