We present the first analysis of a zero-gap bipolar membrane water electrolyzer fed with liquid water. Our electrolyzers feature a high-pH environment for the oxygen evolution reaction and a low-pH environment for the hydrogen evolution reaction. The advantages of proton exchange membrane water electrolysis can be combined with those of anion exchange membrane water electrolysis by including a water splitting bipolar interface. First, we develop a KOH-free anion exchange membrane electrolysis cell. The cell's alkaline anode serves as an integral building block on the path to a bipolar system. In a second step, we use this building block to investigate the cell operation characteristics of various cell configurations. We study the cell performance as the bipolar interface is shifted progressively toward the anode. A bipolar membrane with and without a water splitting catalyst resulted in cell current densities of 450 and 5 mA cm −2 at cell voltages of 2.2 V, respectively. Upon moving the bipolar interface directly between the acidic membrane and the high-pH anode, we achieved current densities of 9000 mA cm −2 at cell voltages of 2.2 V. Our study demonstrates the potential of this water electrolysis configuration, which should be adopted for further scientific studies and may show promise for future commercial water electrolysis systems.
In this work gas diffusion electrode (GDE) half-cells experiments are proposed as powerful tool in fuel cell catalyst layer evaluation as it is possible to transfer the advantages of fundamental methods like thin-film rotating disk electrode (TF-RDE) such as good comparability of results, dedicated elimination of undesired parameters etc. to relevant potential ranges for fuel cell applications without mass transport limitations. With the developed setup and electrochemical protocol, first experiments on different Pt/C loadings confirm excellent reproducibility. Thereby mass-specific current densities up to 30 A mg Pt −1 at 0.6 V vs. RHE are achieved. From a methodological perspective, good comparability to single cell measurements is obtained after theoretical corrections for temperature and concentration effects. In comparison to previous studies with GDE half-cells, polarization curves without severe mass transport limitations are recorded in a broad potential window. All these achievements indicate that the proposed method can be an efficient tool to bridge the gap between TF-RDE and single cell experiments by providing fast and dedicated insights into the effects of catalyst layers on oxygen reduction reaction performance. This method will enable straightforward and efficient optimization of catalyst layer composition and structure, especially for novel catalysts, thereby contributing to the performance enhancements of fuel cells with reduced Pt loading.
The
electrochemical activity of modern Fe–N–C electrocatalysts
in alkaline media is on par with that of platinum. For successful
application in fuel cells (FCs), however, also high durability and
longevity must be demonstrated. Currently, a limited understanding
of degradation pathways, especially under operando conditions, hinders
the design and synthesis of simultaneously active and stable Fe–N–C
electrocatalysts. In this work, using a gas diffusion electrode half-cell
coupled with inductively coupled plasma mass spectrometry setup, Fe
dissolution is studied under conditions close to those in FCs, that
is, with a porous catalyst layer (CL) and at current densities up
to −125 mA·cm–2. Varying the rate of
the oxygen reduction reaction (ORR), we show a remarkable linear correlation
between the Faradaic charge passed through the electrode and the amount
of Fe dissolved from the electrode. This finding is rationalized assuming
that oxygen reduction and Fe dissolution reactions are interlinked,
likely through a common intermediate formed during the Fe redox transitions
in Fe species involved in the ORR, such as FeN
x
C
y
and Fe3C@N–C.
Moreover, such a linear correlation allows the application of a simple
metricS-numberto report the material’s stability.
Hence, in the current work, a powerful tool for a more applied stability
screening of different electrocatalysts is introduced, which allows
on the one hand fast performance investigations under more realistic
conditions, and on the other hand a more advanced mechanistic understanding
of Fe–N–C degradation in CLs.
We present the first combination of a bipolar interface fuel cell with a commercial Fe–N/C catalyst as an alkaline cathode and a PGM-based, acidic anode, both separated by a proton exchange membrane (PEM).
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