Photoelectrochemical water treatment using solar cells and Earth abundant materials

Abstract

The
worldwide availability of safe and clean drinking water constitutes one
of the main challenges of our era. Unfortunately, due to
progress-related issues such as global warming, population growth and
industrial development, the availability and quality of
drinking water is expected to deteriorate in the coming years, posing
new threats for humans and the environment. In view of these
predictions, it becomes increasingly necessary to develop novel,
economical and easily scalable methods for water treatment.





Within the context of this thesis, two novel devices for water treatment
based on solar energy and Earth-abundant materials are proposed: a
photoelectrochemical (PEC) cell using amorphous silicon carbide
(a-SiC:H) photoelectrodes and a PV/electrochemical system
based on graphite electrodes. In order to evaluate their performance,
both systems are tested in the degradation of recalcitrant organic
pollutants.





In the photoelectrochemical cell, a-SiC:H was used first as a photoanode
(n-i-p structure), and afterwards as a photocathode material (p-i and
p-i-n structures).  In both photoelectrode configurations, the
degradation of phenol was monitored under different
applied bias voltages. Additionally, photoresponse measurements were
recorded in order to determine the behaviour of the photoelectrodes in
the solution. Unfortunately, none of the photoelectrode configurations
were able to develop noticeable photocurrents,
resulting in a poor water treatment performance.





With regard to the PV/electrochemical system, the graphite electrodes
were first tested under an external power supply. Here, the
electrochemical oxidation of phenol was studied in detail under
different applied voltages. Additionally, the chemical oxygen demand
(COD) was measured in order to identify intermediate compounds in the
reaction. Overall, it was found that the optimum voltage for the
degradation reaction was 1.6V (80% phenol removal, 59% COD reduction).
In addition to this study, the effect of an alternative
copper counter-electrode was investigated, and the degradation of an
organic dye (methylene blue) was examined. Finally, several PV
structures were proposed for the integration with the graphite
electrodes. The best overall performance was achieved by two micromorph
solar cells connected in series. However, in terms of utilized area, an
individual a-Si:H/a-Si:H tandem cell was the most appropriate choice