(486c) New Reactor Concept for Photocatalytic Hydrogen Evolution Under Sunlight Irradiation

New reactor concept for photocatalytic
hydrogen evolution under sunlight irradiation

M. Schröder, M. Schwarze, K. Kailasam, A.
Thomas, R. Schomäcker

Technische Universität Berlin,
Institut für Chemie, Straße des 17. Juni 124, 10623 Berlin

The depletion of fossil fuels and increase of global
warming lead to a high demand for alternative energy sources that are clean,
cheap and renewable. In addition to wind, water and solar energy, electricity
generation via fuel cells is one of the most promising "green energy"
sources of the future and therefore hydrogen will become more and more
important. But the production of hydrogen by petrochemical routes which are the
most applied technologies, are based on fossil fuels and emit CO₂. Thus,
the production of hydrogen from water via sunlight is considered as a
"Dream Reaction" for hydrogen evolution. Currently different groups
are working with this discipline of "green energy" to develop new photocatalysts which are able to split water into hydrogen
and oxygen or to reduce water to hydrogen with the assistance of sacrificial
reagents. Within the interdisciplinary project "Light2Hydrogen",
which is funded by the "Bundesminesterium für Bildung und Forschung", homogeneous and heterogeneous photocatalysts are synthesized and analyzed for efficient
utilization of solar energy in photocatalytic
hydrogen production. To date, homogeneous catalyst in this project have reached
a hydrogen production rate of up to 20 mL / h ^[1] and  the most efficient heterogeneous photocatalyst, which is a mesoporous
carbon nitride (mpg-C₃N₄), reaches a hydrogen production
rate of up to 2 mL/h (Xenon lamp) ^[2].  To generate power from the produced hydrogen,
for example in combination with a fuel cell, it is important to design a
scalable photoreactor which is combinable with other devices
like hydrogen storage and electricity generation. Therefore, a new photoreactor was designed which (a) has a planar window for
a defined irradiation with less reflection, (b) uses the pressure increase to
follow the reaction and (c) allows a controlled release of the produced
hydrogen during the process. The reactor allows quantitative testing of
different catalyst materials, kinetic investigations and to calculate the
degree of efficiency based on the irradiated energy.

Figure 1: Setup for photorcatalytic investigations (left) and front view of
reactor (right).

In this new photoreactor,
kinetic investigations of mesoporous carbon nitrides as
photocatalysts were performed under sunlight
simulation. A hydrogen evolution rate of 0,55 mL/h is obtained under optimized
reaction conditions. The catalyst is stable and photocatalytic
activity is retained after several dark periods as shown in figure 2.

Figure 2: Volume of hydrogen
as function of time for several light and dark periods

This contribution will introduce the new photoreactor concept and show some results of the kinetic investigations.

[1]
F. Gärtner et al., Chem. Eur. J. 17, 2011, 6998-7006

[2] K. Kailasam et al.,
Energy Environ Sci 4, 2011, 4668-4674