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Journal of Science and Technology in the Tropics 73
praseodymium in its overall construction. Additionally the battery uses up to five
times as much nickel metal as it does lanthanum and a small amount of cobalt.
Thus the manufacturing of a NiMH battery pack requires a lot of rare metals as
well as a lot of engineering.
The difference between a NiMH battery and a lithium-ion battery is primarily
that the NiMH battery has been used in over a million full hybrids, whereby most
of the full hybrid cars built in the last decade primarily by Toyota, Honda, and
Ford are still on the road and provide daily testimony to the reliability of the
NiMH battery pack for full hybrid operation [62].
Although the current interest for rare earths use is now in NiMH batteries,
rare earth elements are also added to other types of batteries such as redox flow
battery [63] and lithium-ion batteries. It was reported that the doping of lithiumion
batteries with lanthanum resulted in reduction of crystal size to the nanoscale,
increase of conductivity and diffusion rate of lithium ion. The results confirmed
that rare earth doping is an effective method for improving electrochemical
properties of the promising alternative cathode [64].
Rare earths in solar cell
Fossil fuels are still the main energy resources that drive the economies of the world
today. Predicted exhaustion and limited resources of fossil fuels, combined with
energy-hungry economies due to modernization and industrialization, coupled
with the emission of environmental harmful greenhouse gases have stimulated
development of sustainable renewable energy sources. Among many others, solar
power is one of the most promising renewable energy sources as an alternative to
our continued dependence on fossil fuels.
Conventional solar cells are manufactured with high purity and expensive
silicon materials, using production methods that consumed high amounts of
energy. For these reasons, silicon solar cells have not become very popular even
though their conversion efficiency has reached between 15% and 20% [65, 66].
Gratzel et al. in 1991, had formulated in their lab an innovative solar cell based
on dye-sensitized colloidal TiO 2
that is set to become a low-cost alternative to
the conventional silicon-based solar cell [67]. Since the first introduction of
dye-sensitized solar cell (DSSC) by the Gratzel’s group, the improvement on
conversion efficiency of DSSCs has been reported every year. Current focus and
interest to extract higher conversion efficiency on DSSCs, aiming to overtake the
best conversion efficiency achieved by silicon-based solar cell, falls in four major
areas [68]: development of sensitizing materials; new anodic materials; use of
various electrolytes; and modification of anodic materials.
To improve on the harvesting of incident light, thus increase the photocurrent
of the DSSC, many sensitizing materials have been synthesized. However, the
best of these sensitizing dyes can only absorb visible light in the wavelength