Green and renewable energy is important to our environment, for sustainable energy supply, and offers new opportunities for economical growth. In the past, materials research has played an essential role in the development of the science bases necessary for green energy technology. In this talk, I will discuss two recent examples using first-principles density functional theory to predict new materials that are relevant to our energy mission. In particular, I will discuss how to optimize the electronic structures of titanium oxide for water splitting using unconventional codoping. I will also discuss using graphene oxide as a light substrate to anchor transition metal element for enhanced binding to non-polar molecules such as the dihydrogen for room-temperature storage in solids.