How the Porous Transport Layer Interface Affects Catalyst Utilization and Performance in Polymer Electrolyte Water Electrolysis

Abstract

Cost reduction and fast scale-up of electrolyzer technologies are essential for decarbonizing several crucial branches of industry. For polymer electrolyte water electrolysis, this requires a dramatic reduction of the expensive and scarce iridium-based catalyst, making its efficient utilization a key factor. The interfacial properties between the porous transport layer (PTL) and the catalyst layer (CL) are crucial for optimal catalyst utilization. Therefore, it is essential to understand the relationship between this interface and electrochemical performance. In this study, we fabricated a matrix of two-dimensional interface layers with a well-known model structure, integrating them as an additional layer between the PTL and the CL. By characterizing the performance and conducting an in-depth analysis of the overpotentials, we were able to estimate the catalyst utilization at different current densities, correlating them to the geometric properties of the model PTLs. We found that large areas of the CL become inactive at increasing current density either due to dry-out, oxygen saturation (under the PTL), or the high resistance of the CL away from the pore edges. We experimentally estimated the water penetration in the CL under the PTL to be ≈20 μm. Experimental results were corroborated using a 3D-multiphysics model to calculate the current distribution in the CL and estimate the impact of membrane dry-out. Finally, we observed a strong pressure dependency on performance and high-frequency resistance, which indicates that with the employed model PTLs, a significant gas phase accumulates in the CL under the lands, hindering the distribution of liquid water. The findings of this work can be extrapolated to improve and engineer PTLs with advanced interface properties, helping to reach the required target goals in cost and iridium loadings.

Ultrathin Microporous Transport Layers: Implications for Low Catalyst Loadings, Thin Membranes, and High Current Density Operation for Proton Exchange Membrane Electrolysis

“…From previous studies, [43,44] it is known that the in-plane current density distribution at the CL is highly dependent on the interface properties, where smaller feature sizes from the particles and pores (like those in the MPL) lead to a more homogeneous current distribution. We hypothesize that specifically for thin membranes, a more homogeneous current distribution can reduce the crossover which has been related to the supersaturation of hydrogen in the cathode catalyst layer.…”

Microporous transport layers facilitating low iridium loadings in polymer electrolyte water electrolysis

“…The protocols for the electrochemical performance tests were similar to those described previously. 36,39,44,79 For the electrochemical performance, a Biologic VSP-300 (Bio-Logic SAS, France) potentiostat is used, allowing for simultaneous high-frequency resistance (HFR) measurements while recording the polarization curves. The cells were conditioned at 5 bar in N 2 (g)/H 2 O(l) for at least 12 h, followed by a potentiostatic break-in cycle protocol (2.0-2.6 V, 50 1C, 10 bar).…”

“…[33][34][35][36][37] In particular, the interface between the PTL and the CL contributes extensively to the efficient use of the CL. [38][39][40][41][42][43][44] Schuler et al correlated the PTL properties with the electrochemical performance, showing that the PTL surface properties significantly affect the CL utilization. 38,39 Lopata also investigated the contribution of the PTL/CL interface at different Ir loadings.…”

Screening potential anodic chemistry in lieu of the oxygen evolution reaction in electrolysis systems: the road to practical application

“…15 (2) Current collector (CC), which directly contacts the catalyst layer, providing electrical contact and pores for the transfer of reactants/products. [205][206][207] In a structure resembling the PEM electrolyzer, CC is also termed as the porous transport layer (PTL), which could be porous Ti sheet, Ti felt or carbon fiber paper. 5 (3) Electrolyte, the space between the cathodic and anodic catalyst layer, providing the ionic conduction.…”