Integration and Performance of Porous Transport Layer Materials Operated at High Pressure

Cost reductions down to at least 2 $/kg H2 are needed for electrolysis to compete with H 2 produced via steam methane reforming. [1] Pressurized H 2 O electrolysis further reduces costs associated with H 2 compression but increases the likelihood of the formation of flammable mixtures of H 2 and O 2 at the anode. Furthermore, regular shutdowns increase the cost of hydrogen due to slower offset of capital costs, and result in shorter stack lifetimes due to faster degradation. [2] Ultimately, it is desirable to operate thin membranes at elevated pressures such as, for example, 30 bar cathode with minimal shutdown events. Under such conditions, the membrane is pushed against the porous transport layer (PTL) causing undesired membrane and catalyst layer deformation. These deformations can lead to increased crossover and efficiency losses. In this presentation, we scrutinize the effect of different commercial porous transport layers on both crossover and efficiency over a cathode pressure range up to 30 bar. In the presented work, results from PTLs tested using H2NEW’s standard FuGeMEA configuration at incremental cathode pressures of 0, 10, 20, and 30 bar are discussed. Electrochemical characterization techniques including polarization curves and electrochemical impedance spectroscopy are used to decouple kinetic and ohmic losses. Gas chromatography is employed in a current density range between 0.1-2 A/cm 2 to measure the hydrogen concentration in the anode O 2 effluent. [3] Structure-performance relationships are further developed using the following techniques: i) ex-situ x-ray tomography to measure PTL morphological properties; ii) post mortem focus variation optical profilometry to measure PTL induced deformation onto the membrane; and iii) PTL contact resistance measurements to isolate the contribution of electrical resistance at the PTL. As shown in figure 1 a), trends in cell voltage as a function of PTL are dominated by the high frequency resistance (HFR). In turn, HFR values are determined by PTL porosity. A higher porosity leads to higher HFR due to higher contact resistances. While electrochemical performance was measured with Pt coated PTLs, crossover measurements were performed using Ir coatings to avoid recombination of H 2 at the anode PTL surface. As shown in figure 1 b), this approach enabled us to ascribe increases in H 2 crossover to PTL induced deformation. In this talk, we will discuss such results to provide insight into the effect of PT