Impact of Shut-Down Procedures on Performance Recovery of Proton Exchange Membrane Fuel Cells

Abstract

It has been noticed that after intentional or unintentional interruption of fuel cell operation or durability testing, such as due to equipment maintenance, normal start-up/shutdown procedure, system failure, overnight rest, continuous electrochemical in situ testing, etc., its performance often improves. This indicates that some of the performance loss is recoverable. The goal of this study is to investigate the impact of shutdown procedure and duration of the shutdown period on PEM fuel cell rejuvenation. An already conditioned standard 50 cm2 (single) fuel cell was exposed to an accelerated stress test (AST) protocol consisting of voltage cycling, designed to target electrocatalyst degradation, but with the intentional recovery periods (so-called soak time steps) every 2500 voltage cycles. Before and after every intentional soak time, a series of diagnostic methods (namely polarization curves, electrochemical impedance spectroscopy, cyclic voltammetry, linear sweep voltammetry) were performed. Different shutdown procedures, as well as different duration of the soak time period were tested and their impact on performance recovery evaluated. Figure 1 shows degradation as calculated electrochemical surface area loss during AST and recovery after each shutdown period. The results suggest that cause of the reversible degradation could be accumulated water within the cell and/or presence of oxygen within the catalyst layer leading to formation of Pt oxides on the catalyst surface. The prolonged soak time step reduces recovery effect, while rapid reduction of the cell temperature with ice proved to be counterproductive for performance recovery. Shutdown procedure without shortly-connected resistor has shown no effect on recovery. Shutdown procedure without nitrogen purge proved to be the most effective for performance recovery. Figure 1