Electrochemical Surface Area (ECSA) is the portion of the catalyst layer electrochemically available to participate in electrode reactions inside a Polymer Electrolyte Fuel Cell (PEFC). ECSA is an important metric that diagnoses the performance/degradation of a catalytic layer and allows the development of new electrodes. This study aims to describe the behavior of the ECSA as a function of cell operating temperatures based on a self-designed experimental based on two approaches. The first is through an analytical-theoretical analysis, and the second is through empirical correlations that fit the experimental curves obtained. The primary variable to study in the present work is temperature. Based on previous studies, the temperature is one of the most influential variables that affect fuel cell efficiency.

A single PEFC with an active area of 25cm², a woven carbon cloth gas diffusion layer, a microporous layer, catalytic layer support with 0.5 mg cm^-2 of Platinum on carbon, and Nafion 212 ® membrane were used to perform this study. The temperature range was varied in the range of 40 - 80 ^oC in steps of 10 °C, and a 100% of Relative Humidity on inlet gases, i.e., hydrogen and nitrogen, were settled at 100%. The characterization of the ECSA was performed with an in-situ cyclic voltammetry test, and the voltage sweep was conducted from 0 to 0.8 V. Finally, the volumetric flow was fixed at 0.1 L/min for both gases hydrogen on the anode side and nitrogen on the cathode side. The results show that the electrochemical surface area (ECSA) of the cathode catalyst decreases drastically as the operating temperature of the cell increases; this is due to the decrease of active sites by the fewer hydrogen ion pathways reaching higher temperatures. Consequently, the empirical correlation proposed for the electrochemically active area in this study helps the catalyst layer's diagnosis and predicts the level of performance for different temperatures.