The fuel cell is similar to a battery. It produces electricity using chemicals. The chemicals are usually very simple, often just hydrogen and oxygen.

Lithium ion batteries are a type of rechargeable battery in which a lithium ion moves between the anode and cathode.

Recently, solar cells have drawn great academic and industrial attentions as a promising candidate of future energy source.

Electrochromism, the reversible change in optical properties when a material is electrochemically oxidized or reduced, has a long history of fundamental and practical interest.