In-Situ Analysis of Voltage Losses at the Porous Transport Layer in a PEM Water Electrolyzer Cell

Abstract

Proton exchange membrane electrolyzer cells (PEMECs) can produce high purity hydrogen gas by performing an electrochemical water splitting process. The technology is carbon neutral when coupled with renewable energy sources such as solar, wind, or hydro [1-3] and a pillar for the proposed realization of a hydrogen based energy cycle. Polarization curve and electrochemical impedance spectroscopy (EIS) are the most widely used techniques for assessing the performance of PEMECs [4], and numerous mathematical models have been developed for analyzing the voltage losses of the cell [5, 6]. Modeling work requires the definition of assumptions that are typically experimentally verified to demonstrate the validity of the model. Experimental results that give insights into the workings of the device enable further refinement of the model and improvement of the results. In this work, the voltage losses at the porous transport layer of the cell are experimentally determined using a four-wire through plane measurement configuration. Figure 1(a) shows a schematic of the measurement principle. Sensing wires are added to the interface between porous transport layer (PTLs) and electrode, which enables to observation of two additional internal voltages. Figure 1(b) shows the DC equivalent electrical circuit of the configuration. It consists of the combined anode side resistance (Rcas ), the catalyst coated membrane (CCM) resistance (RCCM ) and the combined cathode side resistance (Rccs ). By measuring the cell voltage V1 , and the internal voltages V2 and V3 during operation, the three resistances can be calculated using the following equations. The cell resistance Rcell is measured via AC impedance and constitutes the high frequency resistance of the cell. Rcas=(V1-V2)/i (1) Rccs=(V2-V3)/i (2) RCCM=Rcell-Rcas-Rccs (3)In this study, we applied the introduced measurement strategy and investigated the voltage losses of different anode PTLs in PEMEC. Figure 2 shows the measured voltage and calculated resistances of Ir coated and uncoated 125 µm thick Ti felt PTLs. The data indicate that Ir coating on Ti felt significantly reduces the electrical resistances of the PTLs and the interfacial contact resistance [7]. Results obtained with the introduced voltage sensing configuration will be presented and discussed. They include the effects of PTL coatings, operating temperature, and degradation processes on the through plane voltage loss distribution.