Operando monitoring of the evolution of triple-phase boundaries in proton exchange membrane fuel cells

The electrochemical reactions in proton exchange membrane fuel cells take place at the interface between the proton conductive electrolyte, gases, and catalyst active site, or the so-called triple-phase boundary. The triple -phase boundary area can increase through catalyst layer designs and hydrogen fuel cell operations. While catalyst layers are commonly characterized using physical methods, the impact of hydrogen fuel cell operations on triple-phase boundaries is significantly more challenging to analyze, with operando electrochemical charac-terizations currently lacking the necessary accuracy and sensitivity to capture these evolutions. Herein, we introduce an innovative approach to monitoring triple-phase boundary evolutions by simultaneously capturing the ohmic resistance and double-layer capacitance in transient operations using high-frequency zero-phase impedance spectroscopy. The operando catalyst layer utilization quickly reduces through-out dehydration, flooding, excessive load increase, and cell degradations. This approach precisely pinpoints how proton transport, electron transport and oxygen diffusion can altogether reduce the triple-phase boundary area. This new analysis, conducted using commercial materials, unravels the evolutions of the active site and electrolyte interactions throughout the hydrogen fuel cell operations and lifecycle, evidencing a rapid evolution in the triple-phase boundary area throughout the hydrogen fuel cell operations.