Gas diffusion electrode (GDE) setups have very recently received increasing attention as a fast and straightforward tool for testing the oxygen reduction reaction (ORR) activity of surface area proton exchange membrane fuel cell (PEMFC) catalysts under more realistic reaction conditions. In the work presented here, we demonstrate that our recently introduced GDE setup is suitable for benchmarking the stability of PEMFC catalysts as well. Based on the obtained results, it is argued that the GDE setup offers inherent advantages for accelerated degradation tests (ADT) over classical three-electrode setups using liquid electrolytes. Instead of the solid-liquid electrolyte interface in classical electrochemical cells, in the GDE setup a realistic three-phase boundary of (humidified) reactant gas, proton exchange polymer (e.g. Nafion) and the electrocatalyst is formed. Therefore, the GDE setup not only allows accurate potential control but also independent control over the reactant atmosphere, humidity and temperature. In addition, the identical location transmission electron microscopy (IL-TEM) technique can easily be adopted into the setup, enabling a combination of benchmarking with mechanistic studies.
This review attempts to summarize recent advances with respect to solution-processable molecular semiconductors having 2,1,3-benzothiadiazole or its fluorine substituted derivatives as electron-acceptor units published in the last few years. The relationship between the structure, optoelectronic properties, and photovoltaic performance of these molecular semiconductors is discussed.
In
the present study, different concepts for the development of
bifunctional oxygen reduction reaction/oxygen evolution reaction (ORR/OER)
electrocatalysts are explored and compared. Bifunctional ORR/OER catalysts
are often suggested to improve the stability during startup and shutdown
of fuel cells. Furthermore, they have been proposed for the so-called
unitized regenerative fuel cells (URFCs) that would allow a closed
loop system to use and produce hydrogen on demand. We compare the
electrocatalytic performance of conventional Pt
x
Ir
y
alloy nanoparticles (NPs)
with Pt–IrO2 NP composites (nanocomposites), both
immobilized onto a commercial carbon support. The Pt–IrO2 nanocomposites thereby consist of a mixture of Pt NPs and
IrO2 NPs. By probing the electrocatalytic performance before
and after exposing the electrocatalysts to accelerated degradation
tests (ADTs), it is shown that the Pt–IrO2 nanocomposite
concept offers advantages but also some disadvantages over the conventional
alloy concept. In particular, it is shown that while the nanocomposites
are initially less active for the ORR because of an interparticle
effect, their performance is less affected by the ADTs. However, all
the tested catalysts experience a decline of the Ir/Pt ratio upon
ADT treatment, highlighting the limiting value of Ir as an OER catalyst
for startup–shutdown protection in fuel cells as well as the
challenging stability requirements for URFCs.
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