Fuel cells and electrolyzers efficiently convert chemical energy into electricity or hydrogen. Commercial testing has begun. 
Electrochromic devices contribute to energy efficiency in buildings & vehicles.
Hydrogen storage is possible with nanofibers that can adsorb hydrogen gas molecules.
Photovoltaic cells include metal oxides.
Rechargeable batteries have electrodes with metal.
Supercapacitors include metal oxides used as electrode materials.
Thermoelectric devices can convert waste heat into electricity.