In-situ X-ray computed tomographic investigation of the electrochemical interfaces in a miniaturized proton exchange membrane water electrolyzer

X-ray computed tomography (XCT) provides a non-invasive diagnostic tool for simultaneously analyzing the catalyst-coated membrane (CCM), porous transport layer (PTL), and gas diffusion layer (GDL) of a proton exchange membrane water electrolyzer (PEMWE). In this work, an X-ray-compliant miniaturized PEMWE (mPEMWE) is designed for in-situ XCT visualization of PTL-CCM and GDL-CCM interfaces under electrolyzer operating conditions. Electrochemical testing and visualization of cells with variable land-channel configurations demonstrate that wide lands provide the highest cell performance, resulting from optimal component compression under the channel and land areas. Thin lands cause excessive component compression under the land areas, resulting in poor cell performance, whereas wide channels lack sufficient component support, causing inferior cell performance. The changes in the electrochemical interfaces are investigated at the beginning-of-life and end-of-test stages at 300 h by comparing in-situ XCT images and electrochemical performance using thick Nafion® 115 and thin Nafion® 212 membranes. Severe deformities at the PTL-CCM interface are observed at EOT, with semicircular imprints on the anode catalyst layer resulting from membrane expansion into the PTL crevices. Discontinuity in the anode catalyst layer at the PTL-CCM interface is correlated with increased overpotential, and ohmic and charge transfer resistance at EOT. This interfacial deformation mechanism is consistent across both thick and thin membranes, but is more severe in the thin membrane due to additional indentations and heterogeneity at the PTL-CCM interface. Thus, the stability of the PTL-CCM interface is deemed critical for long-term PEMWE performance and durability.