Transient response of low platinum-loaded proton exchange membrane fuel cells with various cathode catalyst layer compositions

Exploring catalyst layer (CL) compositions is crucial for achieving high-performance, low platinum (Pt)-loaded proton exchange membrane (PEM) fuel cell cathodes, yet transient effects of these compositions are often overlooked. This study experimentally measures dynamic cell responses in different Pt-loaded CLs and develops a transient non-isothermal two-phase pseudo-three-dimensional model incorporating microstructural features using a single serpentine-channel cell in Galvano-dynamic mode. The model is first employed to capture voltage responses in different Pt-loaded CLs and later is utilized to simulate voltage transients of cells with varying ionomer-to‑carbon (I/C) ratios, mass fraction of bare carbon particles, and CL thicknesses, focusing on transients of cathode overpotential, CL ionomer potential loss, and water saturation. An abrupt increase in current density among various Pt-loaded CLs triggers a voltage undershoot followed by an overshoot, with a gradual voltage decline over time. Transient responses in CLs with varying I/C ratios are dominated by CL ionomer potential loss, which increases during abrupt current density rises but decreases with water production at a steady current density. Higher bare carbon mass fractions primarily affect cathode overpotentials, causing greater undershoots, while thicker CLs exhibit more pronounced undershoots and longer transition times, driven by CL ionomer potential loss and water saturation dynamics.