Effects of mechanical pressure on anion exchange membrane water electrolysis: A non-negligible yet neglected factor

Commercialized implementations of anion exchange membrane water electrolysis (AEMWE) require stable operation at high current density. To achieve this, ohmic, electrochemical and concentration polarizations are supposed to be exceedingly suppressed. Among all crucial materials, porous electrodes with catalyst coatings extensively affect the above polarizations, which are highly sensitive to specific mechanical pressure for cell assembly. However, the imposed mechanical pressure and its effects on cell performance are rarely reported in AEMWE cells. Here, quantitative characterizations of mechanical pressure and its effects on i) physical properties of catalyst coated electrodes and ii) corresponding single-cell performance are comprehensively investigated. First, the imposed mechanical pressure on membrane electrode assembly (MEA) is controlled by different total thickness gaps between anode/cathode and poly-tetra-fluoroethylene (PTFE) gaskets (Δd = 0, 100, 200, 300 μm). Second, the above resulted distributions of mechanical pressure are quantitatively studied by a mechanical pressure tracking method. Third, the influence of the mechanical pressure on the physical properties of the electrodes and cell performance are demonstrated. It is proved that the mechanical pressure of ca. 0.5 MPa is comprehensively beneficial for suppressing internal resistance (R_Ω) and charge transfer resistance (R_ct), with slightly increased mass diffusion resistance (R_md) and hydrogen crossover. This study unveils the intrinsic effects of mechanical pressure on cell performance and provides critical insights into baseline benchmarking and single-cell even stack optimization.