H2Tech - Q4 2021 - 19

FUTURE OF HYDROGEN ENERGY
such as diffusion may be responsible for
such a shift, while fast processes may
be able to perfectly " follow " the voltage
perturbations. At high frequencies, slow
processes will only " see " the average voltage;
they will not be able to respond to
the voltage perturbations.
Instead, fast processes, such as the
reaction kinetics, will be responsible
for the shift in the response at high frequencies.
Additionally, the amplitude of
the response (δI) may also vary at different
frequencies.
By sweeping over different frequencies,
the method is able to separate processes
with different time constants.
The time shift and the current response's
amplitude to the voltage perturbation
are reflected in the complex impedance,
where a shift in time is reflected in the
imaginary part of the impedance. The
absolute value of the impedance reflects
the proportionality of the response.
For a fuel cell, the impedance response
gives insight into several fuel
cell properties and processes. At high
frequencies, short-time-scale processes,
FIG. 4. Results from an impedance spectroscopy simulation of a fuel cell unit cell. The activity of
the cathode catalyst is varied in four different frequency sweeps.
such as capacitance, electrochemical reactions
and local resistances, affect the
impedance. On the other hand, at low
SPECIAL FOCUS
frequencies, phenomena such as the diffusion
in the pore electrolyte contribute
to the impedance. Frequency sweeps can
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H2Tech - Q4 2021

Table of Contents for the Digital Edition of H2Tech - Q4 2021

Contents
H2Tech - Q4 2021 - Cover1
H2Tech - Q4 2021 - Cover2
H2Tech - Q4 2021 - Contents
H2Tech - Q4 2021 - 4
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H2Tech - Q4 2021 - 48A
H2Tech - Q4 2021 - 48B
H2Tech - Q4 2021 - 49
H2Tech - Q4 2021 - 50
H2Tech - Q4 2021 - Cover3
H2Tech - Q4 2021 - Cover4
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