ABSTRACT
Electrochemical-energy conversion technology has been widely investigated to meet the ever-increasing energy demand and environmental consideration. Electrochemical-energy conversion is usually classified as either chemical-to-electrical or electrical-to-chemical processes, which are used typically in hydrogen fuel cells and water splitting, respectively. Hydrogen fuel cell and water splitting are two typical electrochemical-conversion technologies that represent chemical-to-electrical and electrical-to-chemical conversion, respectively. Their electrochemical-reaction processes, mechanisms, and electrocatalyst materials are introduced and discussed separately to understand the fundamentals of the four electrochemical reactions. Since electrolysis of water was first reported in 1789, the technology has been widely researched and applied over the last two centuries. Based on their low cost, high durability, and unique physical and chemical properties, carbon nanomaterials are appealing to catalyze electrochemical-energy conversion reactions efficiently. Like fullerenes, carbon nanotubes have the same property for entrapping other element atoms into their molecular structure, which helps to increase the number of active sites, enhance durability, and improve methanol resistance.
