7 research outputs found
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In-Operando Measurement of Hydrogen Crossover in Proton Exchange Membrane Electrolysis Cells at Differential Pressures
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Mathematical Modeling of the Performance-Degradation Mechanisms of Cation-Contaminated Proton-Exchange-Membrane Water Electrolysis
The role of hydrogen as a commercial energy carrier is dependent on the development of robust processes to convert hydrogen into usable electricity as well as produce hydrogen at large scales. Proton-exchange-membrane water electrolysis (PEMWE) is a leading technology with the potential to produce hydrogen at projected consumption rates. In PEMWE, water is electrochemically split into hydrogen and oxygen gas using a membrane—electrode assembly, which uses a membrane capable of transporting both water and protons. Reactant water containing cationic impurities have been observed to degrade cell performance. Thus, developing an understanding of the influence of cationic contaminants is important to developing mitigation and recovery strategies for PEMWE systems.
In the current work, mathematical models were developed to provide insight into the mechanisms of performance degradation due to cationic contaminants. The models are non-isothermal continuum models that describe multi-phase porous flow, electrochemical reactions, and concentrated-species transport in both the gas membrane, and ionomer phases. Simulations were performed in steady-state and transient operational modes for various cationic species at several ionic concentrations. The calibration and fitting of the models were performed using experimental measurements performed by the National Renewable Energy Laboratory. The mathematical models suggest that gradients facilitate the adsorption of cationic contaminants in reactant water, which subsequently accumulate in the cathode catalyst layer, as shown in Figure 1(a), and inhibit the PEMWE hydrogen-evolution reaction (HER) that consume protons and electrons to produce hydrogen gas. The models suggest that protonic conductivity is not significantly affected by low-concentration cationic species, but access to the catalyst active sites in the cathode catalyst layer is severely impeded. As a result, the evolution of hydrogen then proceeds by an alkaline mechanism, where water and electrons combine to produce hydrogen gas and hydroxide ions. An interpolated polarization curve shown in Figure 1(b) suggests that cell operation at high current densities favor the alkaline HER reaction due to the lack of protons in the cathode catalyst layer.
This research is supported by DOE Hydrogen and Fuel Cell Technologies Office, through the H2NEW Consortia.
Figure
How the Porous Transport Layer Interface Affects Catalyst Utilization and Performance in Polymer Electrolyte Water Electrolysis
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
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(Invited) Progress in Nafionâ„¢ Membrane Development for Proton Exchange Membrane Water Electrolyzers
A scalable membrane electrode assembly architecture for efficient electrochemical conversion of CO2 to formic acid
Abstract The electrochemical reduction of carbon dioxide to formic acid is a promising pathway to improve CO2 utilization and has potential applications as a hydrogen storage medium. In this work, a zero-gap membrane electrode assembly architecture is developed for the direct electrochemical synthesis of formic acid from carbon dioxide. The key technological advancement is a perforated cation exchange membrane, which, when utilized in a forward bias bipolar membrane configuration, allows formic acid generated at the membrane interface to exit through the anode flow field at concentrations up to 0.25 M. Having no additional interlayer components between the anode and cathode this concept is positioned to leverage currently available materials and stack designs ubiquitous in fuel cell and H2 electrolysis, enabling a more rapid transition to scale and commercialization. The perforated cation exchange membrane configuration can achieve >75% Faradaic efficiency to formic acid at <2 V and 300 mA/cm2 in a 25 cm2 cell. More critically, a 55-hour stability test at 200 mA/cm2 shows stable Faradaic efficiency and cell voltage. Technoeconomic analysis is utilized to illustrate a path towards achieving cost parity with current formic acid production methods