Chapter 5
Materials for Light
Absorption
5.1 Introduction
In the last chapter the need to find alternative energy resources has been
discussed. It was primarily based on the catalytic aspect of the hydrogen
production. This chapter is mainly focussed on the absorption of sunlight
with semiconducting materials and the absorbed light can be used to produce
hydrogen by splitting the water. Harvesting the sunlight is crucial because
solar energy is the most promising alternative resource which can meet the
growing energy requirement on top of being environmentally benign as compared
to the fossil fuels. Some of the routes to harness the solar energy are
solar cells, thermoelectrics, photoelectrochemical inter-conversion of chemicals
etc 75, 76, 77, 78, 79, 80, 81, 82, 83. Photo-electrochemical routes to produce
chemicals have an added advantage of producing chemicals not just to be used
as fuels but also for other purposes 84.
One of the simplest photoelectrochemical reactions is the splitting of water
into oxygen and hydrogen. The advent of TiO2 as a material to split the
water into hydrogen and oxygen revolutionized the research in the area of
photoelectrochemical energy conversion 83. But the wide bandgap of TiO2
limits its performance only to the ultraviolet (UV) region of solar spectrum.
Despite continuous effort for more than three decades no abundant and efficient
binary compound has been found to accomplish the task of visible light driven
water splitting. The limited search space of binary compounds shifted the focus
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