Environmental Engineering Reference
In-Depth Information
Photoelectrochemical cells for
hydrogen production from solar energy
Tania Lopes, Luisa Andrade &Adelio Mendes
Laboratório de Engenharia de Processos, Ambiente e Energia (LEPAE), Faculdade de
Engenharia da Universidade do Porto, Rua Roberto Frias, Porto, Portugal
10.1 INTRODUCTION
The awareness concerning carbon dioxide emissions and the depletion of fossil fuel
reserves motivates the development of innovative processes to take advantage from
renewable energy sources (Grätzel, 2005). The world power consumption is currently
about 13 TW and it is expected to increase up to 23 TW by 2050 (Dobran, 2010).
With approximately 120 PW of solar energy continuously striking the earth at any
given moment, the challenge in converting sunlight into electricity via photovoltaic
(PV) cells is to reduce the cost per watt of delivered solar electricity (Krol et al., 2008
and Nathan, 2005), which is already approximately 0.65
/Wp for crystalline sili-
con modules. The solar PV technology has greatly evolved in the last decade and
it is now a well-established way to convert solar energy into electric energy, which
accounts presently more than 21 GW installed worldwide (The Energy Report, 2011).
Nevertheless, this technology only works on a daily basis and it largely depends on
the amount of solar radiation available. Thus, an effective method to store energy for
later dispatch is still needed (Trieb, 2005). A practical way to convert sunlight into a
storable energy form is using a photoelectrochemical (PEC) cell that splits water into
hydrogen and oxygen by light-induced electrochemical processes (Grimes et al., 2008).
Hydrogen production via photoelectrochemical water-splitting is a thriving alter-
native that combines photovoltaic cells with an electrolysis system (Bard and Fox,
1995; Khaselev and Turner, 1998). The major advantage is that solar harvesting, con-
version and storage are combined in a single integrated system (Nathan, 2005). The
hydrogen generated by this process has the potential to be a sustainable carbon-neutral
fuel since it is produced from a renewable source and it can be stored or transformed
into other chemicals such as methanol or methane (Grimes, 2008; Zerta, 2008).
a
10.2 PHOTOELECTROCHEMICAL CELLS SYSTEMS OVERVIEW
10.2.1 Solar water-splitting arrangements
Converting sunlight into hydrogen and oxygen through water-splitting can be accom-
plished via different technologies, as sketched in Figure 10.2.1. More specifically, via
three general types of devices:
i
) composed devices - photovoltaic (PV) cell associated
with an electrolyzer or photovoltaic (PV) cell associated with a PEC cell;
ii
) stand
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