Exploring Proton Activity at the Membrane/Electrode Interface with Microelectrodes

Polymer electrolyte membrane (PEM) technology is a key component in low-temperature, high efficiency fuel cells and electrolyzers. Hydrogen fuel cells convert chemical energy from hydrogen into electrical energy, while water electrolyzers do the opposite, using electrical energy to generate hydrogen and oxygen from water. Polymer electrolyte membrane fuel cells (PEMFCs) and water electrolyzers (PEMWEs) are attractive technologies for clean and efficient energy conversion, with wide-ranging applications, including transportation, stationary power generation, and energy storage. These technologies have significant potential to reduce greenhouse gas emissions and dependence on fossil fuels, making them a crucial component of the transition towards a low-carbon economy. The most commonly used PEMs are perfluorinated sulfonic-acid (PFSA) membranes, and they have been extensively studied. However, the proton activity at the membrane-electrode interface under solid-state operating conditions is very challenging to measure and remains unclear. The interfacial proton activity plays a critical role in the kinetic performance, therefore understanding how different polymer properties and operating conditions impact the proton activity will give new insights to improve performance. The proton activity is calculated for equilibrium and reaction conditions through ocv measurements and kinetic fitting to HOR/HER measurements in a three-electrode microelectrode system. Additionally, investigating the impacts of water activity, proton concentration, and equivalent weight offers new insights into the properties and behavior of the local environment.