Water gradient manipulation through the polymer electrolyte membrane of an operating microfluidic water electrolyzer

The key component of a polymer electrolyte membrane (PEM) water splitting electrolyzer is its membrane. Despite decades of research, the transport phenomena occurring within the membrane during electrolysis - which are vital to the device's efficiency - have yet to be fully understood. In this work, controlling the anolyte concentration can effectively be used to tune the PEM water gradient, but it comes with a tradeoff in electrochemical performance. Infrared (IR) imaging is coupled with electrochemical impedance spectroscopy and distribution of relaxation times to elucidate the relationship between membrane hydration and ohmic, kinetic, and mass transport losses. Varied H2SO4 anolyte concentrations manifested water diffusion gradients through the PEM of the electrolyzer, where the strongest water diffusion gradients | Delta lambda(fit) | (relative to open circuit voltage) were observed for the most concentrated anolyte. However, tuning the anolyte concentration came with a tradeoff between a lower ohmic resistance (from 4.4 Omega cm(-2) to 4.0 Omega cm(-2) for 0.1 mol L-1 to 1.0 mol L-1 H2SO4 anolyte) and higher kinetic and mass transport losses accompanied by increasingly unstable performance. These findings showcase the potential of IR imaging when coupled with a microfluidic PEM electrolyzer and electrochemical characterization techniques, and the influence of anolyte concentration for manipulating the PEM water gradient.