Development of sustainable energy sources is an urgent issue to meet growing demand in world energy consumption. Among the various types of sustainable energy fuels such as hydrogen , hydrocarbon, and ammonia are one of the most promising renewable energy source s with a high energy density.

The discovery of efficient catalysts represents one of the most important and challenging issues for the implementation of photoelectrochemical (PEC) or electrochemical fuel production. A critical requirement for outstanding catalysts is not only an abili ty to boost the kinetics of a chemical reaction but also a durability against electrochemical and photo induced degradation. Generally, precious metals, such as platinum, exhibit superior performance in these requirements; however, high cost of the preciou s metal is the biggest barrier to widespread commercial use. To address this critical and lo ng standing technical barrier, I have focused on an intense search for efficient, durable, and inexpensive alternative catalysts such as (1) efficient photoelectroc hemical water splitting catalyst s , (2) Single atomic catalyst for efficient hydrocarbon conversion reaction (3) electrochemical nitrogen reduction to ammonia production as possible hydrogen carrier.