ABSTRACT
In looking to our everyday growing clean-energy needs and to subsidize the environmental damage done by the emissions of convention fuels, the statement of Prof. James Barber seems quite contemporary, that is, our sun is the champion of energy sources, delivering more energy to Earth in an hour than we currently use in a year from fossil, nuclear, and all renewable sources combined. Its energy supply is inexhaustible in human terms, and its use is harmless to our environment and climate (Barber 2009). Therefore, a large number of principal investigation projects are devoted worldwide to generate chemical fuels from sunlight. In this age of light, carbon-neutral water can be considered a fuel of the future. Because when the water is coupled with sunlight at the platform of a photocatalyst, they can produce clean fuels, hydrogen and oxygen. These products are carbon-neutral molecules, which never produce carbon-containing systems and therefore can be treated as clean fuels. Hydrogen can especially be considered as a good energy carrier or fuel for transport, industry, and electricity generation. In this chapter, we discuss the fundamental elements related to efcient hydrogen generation through water splitting. These include articial photosynthesis, the electrochemistry of water splitting, criteria for the selection of photocatalytic material, overpotential, band gap and band edge position in photocatalytic materials, band edge bending of semiconductor efciency (solar to hydrogen conversion), efciencies (turnover number [TON], quantum yield, photoconversion efciency [incident photon-to-current ef- ciency {IPCE} {%}, absorbed photon-to-current efciency {APCE}]), excitonic binding energy, diffusion length and carrier mobility in photocatalyst, and so on. For each of these elements, we discuss the gures of merit, the critical length scales associated with each term, and the way in which these length scales must be balanced for efcient generation of hydrogen. We have to develop the right materials to make it work efciently. For this, scientists of all backgrounds are coming together to beat nature at her own game by treating/setting all of the parameters well, such as light absorption, photogenerated carrier collection, photovoltage, electrochemical transport, and catalytic behavior.
