<p>H₂ is an ideal storable form of energy.  Splitting water produces H₂ and burning it, or even better using it in fuel cells, regenerates water and releases the chemical energy stored in H₂.  Thus H₂ can serve as a recyclable alternative energy source which avoids CO2, a major contributor to global warming.  Electrolysis of water to produce H₂ and H₂ fuel cells require catalysis by Pt, a rare and expensive metal.