Pt loading-dependent effects of hot pressing on ultrasonic-sprayed membrane electrodes for PEM fuel cells

Optimizing the hot pressing process is important for improving the performance of membrane electrode assemblies (MEAs) in proton exchange membrane fuel cells, especially in the pursuit of high-performance and low-Pt fuel cell technologies. This study conducts a comparative analysis of hot-pressing parameters (pressure, temperature, time) on MEAs with conventional (0.48 mg·cm⁻²) and low (0.12 mg·cm⁻²) platinum loadings. Twenty hot-pressed membrane electrodes were fabricated by varying the hot pressing pressure (0–0.6 MPa), temperature (90–170 °C), and duration (1–10 min). The electrochemical properties of the membrane electrodes were analyzed and the structures of the catalytic layer and the proton exchange membrane were characterized. The results show the effect of hot pressing exhibits a significant dependence on Pt loading. For conventional Pt loading MEAs, moderate pressure (0.4 MPa) effectively reduced ohmic and mass transport resistances, while temperatures above the Nafion glass transition point increased electrochemical surface area by 40.10% ∼ 57.42%. However, prolonged pressing (10 min) caused severe performance deterioration, mainly due to ionomer pyrolysis and impeded proton transport in catalytic layer. Optimal parameters were identified as 0.4 MPa, 150 °C, and 3 min, under which the peak power density can be increased by over 12%. In contrast, any hot pressing deteriorated performance in low Pt loading MEAs, attributed to attributed to their thinner and less dense catalyst layer structures, where hot pressing easily leads to pore collapse, thereby reducing catalyst activity and gas transport. 0.24 mg·cm⁻² was identified as the critical threshold for the transition of hot-pressing impacts.