Communication—Contribution of Catalyst Layer Proton Transport Resistance to Voltage Loss in Polymer Electrolyte Water Electrolyzers

Abstract

Mass transport losses (η mt x ) play a significant role at high current densities in polymer electrolyte water electrolyzers (PEWEs). Previous work has shown that η mt x depends on the porous transport layer (PTL) structure, although a clear correlation between the material morphology and η mt x has not been established. In this work, we experimentally determine the overpotential η H + C La associated with the proton transport in the anodic catalyst layer by measuring the ionic resistance in the catalyst layer using electrochemical impedance spectroscopy (EIS) and the transmission-line model. We found that overpotentials, including η H + C La , depend on the PTL morphologic surface properties.

CO2-Assisted Regeneration of a Polymer Electrolyte Water Electrolyzer Contaminated with Metal Ion Impurities

“…The total η mtx of the non-contaminated electrolyzer was subsequently corrected for the R H + CLa to obtain η rest , as the R H + CLc is negligible in this case. 53,55 The analysis of mass transport losses based on the corrections yields a R H + CLc of a contaminated electrolyzer to increase up to 520 ± 32 mOhm cm 2 , which is almost 3 times higher compared to the value obtained from the H 2 /N 2 measurements ( Figure S5).…”

“…Ionic and total mass transport resistance.-The cell voltage is iR-corrected ( Figure 5b) and further analyzed using the Tafel model in order to distinguish between the kinetic and mass transport losses. The mass-transport losses (η mtx ) in PEWE consist of contributions from the anode (η H + CLa ) and cathode (η H + CLc ) catalyst layer proton transport resistances, [53][54][55][56] and the contributions from the other cell components (η rest ): [11][12][13]49…”

“…In an uncontaminated electrolyzer cell, the losses associated to ionic transport in the catalyst layers are dominated by the proton transport resistance in the anode catalyst layer (η H + CLa ). 53,55 The proton transport losses in the cathode catalyst layer (η H + CLc ) is thought to be negligible, due to the low kinetic overpotential of the hydrogen electrode. 53 Since the Gd 3+ experiments have revealed that the ionic contaminant mostly resides in the cathode catalyst layer during constant current operation, the proton transport resistance of the cathode CL (R H + CLc ) is expected to increase, and thereby the η H + CLc .…”

Communication—Pt-Doped Thin Membranes for Gas Crossover Suppression in Polymer Electrolyte Water Electrolysis

“…The lower operational limit (LOL) for the turndown ratio is set by the current density value for a concentration of 2% hydrogen in oxygen and can be determined by solving [8]. The experimentally obtained values for the LOL and the values obtained by solving [8] with the linear regression parameters from Table SI at differential pressures and membrane types are listed in Table SI. The lower values for the LOL from fitting than from the experiment could be due to neglecting the permeation of oxygen to the anode side in [6].…”

“…Hydrogen permeation rate from anode to cathode side in a PEWE cell using pristine NR212 (N212, black), and a Pt doped NR212 obtained by reduction with hydrogen (Pt-N212, green) at ambient cathodic pressures, 5 bara and 10 bara, respectively, and 60 o C (anode: 1 bara). The lines represent a linear fit through the points calculated by [8]. The linear regression parameters are listed in Table SI.…”