Due to the wide applications of acetonitrile as a solvent in the chemical industry, acetonitrile can be present in the air and should be considered a possible pollutant. In this work, the spatial proton exchange membrane fuel cell performance exposed to air with 20 ppm CH 3 CN was studied using a segmented cell system. The injection of CH 3 CN led to performance losses of 380 mV at 0.2 A cm 2 and 290 mV at 1.0 A cm 2 accompanied by a significant change in the current density distribution. The observed local currents behavior is likely attributed to acetonitrile chemisorption and the subsequent two consecutive reduction/oxidation reactions. The hydrolysis of CH 3 CN and its intermediate imine species resulted in NH 4 + formation, which increased the high-frequency resistance of the cell and affected oxygen reduction and performance. Other products of hydrolysis can be oxidized to CO 2 under the operating conditions. The reintroduction of pure air completely recovered cell performance within 4 h at 1.0 A cm 2 , while at 0.2 A cm 2 the cell recovery was only partial. A detailed analysis of the current density distribution, its correlation with spatial electrochemical impedance spectroscopy data, possible CH 3 CN oxidation/reduction mechanisms and mitigation strategies are presented and discussed.