Abstract
Low temperature water electrolysis (LTE) using proton exchange membrane electrolysis cells (PEMECs) is a promising approach for producing green H2 that can use electricity from renewable sources. In practice, H2 is stored and dispensed at high pressures. To alleviate efficiency losses associated with pressurizing the product hydrogen, PEMECs can be operated at high differential pressures, e.g., >30bar on the cathode side. However, high differential pressure operation can result in undesirable H2 crossover to the anode (O2) side. This not only reduces the Faradaic efficiency of the cell, but also can result in flammability hazards.
H2 crossover in PEMECs is a function of both materials properties such as membrane thickness, water uptake, and permeability, and operating conditions such as temperature, differential pressure, and current density. Example data are shown in Figure 1. While thinner membranes are susceptible to higher H2 crossover rates, they are a desirable material to use because they can result in significantly improved cell performance and lower material and production costs. To mitigate safety concerns related to H2 crossover, gas recombination catalyst (GRC) layers can be introduced into the membrane electrode assembly. The GRCs will react the crossover H2 with O2 to produce water, thereby minimizing the amount of H2 entering the O2 stream.
In this talk we will present data from in-operando crossover measurements of PEMECs employing a variety of membrane materials, both with and without GRCs. The experiments are complimented by modeling results that allow further insights into the processes at hand. Multiple temperatures, differential pressures, and current densities are studied. The results will investigate the tradeoff between performance and capturable H2 production that occurs when thinner membranes are used, and how this effect responds to differential pressure operation.
Figure 1