The field of polymer membrane design is primarily based on empirical observation, which limits discovery of new materials optimized for separating a given gas pair. Instead of relying on exhaustive experimental investigations, we trained a machine learning (ML) algorithm, using a topological, path-based hash of the polymer repeating unit. We used a limited set of experimental gas permeability data for six different gases in ~700 polymeric constructs that have been measured to date to predict the gas-separation behavior of over 11,000 homopolymers not previously tested for these properties. To test the algorithm’s accuracy, we synthesized two of the most promising polymer membranes predicted by this approach and found that they exceeded the upper bound for CO2/CH4 separation performance. This ML technique, which is trained using a relatively small body of experimental data (and no simulation data), evidently represents an innovative means of exploring the vast phase space available for polymer membrane design.

Fluxes of the four vanadium cations V2+, V3+, VO2+ and VO2 + through three archetypal membranes were measured as functions of current density. The membranes include a cation-exchange membrane, an anion-exchange membrane, and an initially uncharged membrane. Comprehensive data sets including mass and vanadium sorption, in-plane and through-plane conductivity, diffusive permeability, and transference number were collected to help interpret vanadium fluxes. Conductivity, diffusion coefficient, and transference number appear to be inter-related as predicted by Nernst-Planck theory for the cation-exchange membrane Nafion. The properties do not appear to be as compellingly connected for the anion-exchange membrane FAPQ-330 or polybenzimidazole. The Nernst-Planck formalism, with the Nernst-Einstein approximation, predicts a larger influence of current density on vanadium flux than is observed experimentally for these membranes. Possible explanations for these disparate findings are investigated and discussed.

No abstract

We demonstrate the use of para-polybenzimidazole (PBI) membranes as replacements for Nafion membranes in aqueous HCl oxygen-depolarized electrolyzers. Both para-PBI and densified para-PBI membranes reduce the cell voltage needed at 0.5 A cm–2 by ≥100 mV. We examine the effect of HCl(aq) flow rate, back-pressure, electrolyzer temperature, and, for the densified para-PBI membranes, H3PO4 swell time on electrolyzer performance. Increased proton conductivity, measured as reduced area-specific membrane resistance, is identified as the primary mechanism to explain the improved performance of the electrolyzer.

A new technique involving physical modification after polymerization was developed in which gel polybenzimidazole (PBI) membranes were converted into dense PBI films. Using the polyphosphoric acid (PPA) process, gel PBI membranes were prepared and underwent acid removal followed by a controlled densification step. PBI polymers with rigid PBI backbone structures, such as para-PBI, were prepared as dense films from high-molecular-weight polymers. This approach to produce dense PBI films from gel PBI membranes can allow for new PBI structures that exhibit little to no solubility in organic solvents to be produced as dense films and holds potential for various applications of PBI films. The technique also provided lower associated costs, time, waste generation, and energy consumption, compared to previous methods. The new process and properties of the resulting dense PBI films will be discussed.

Chlorine (Cl2) is a fundamental feedstock material for the chemical industry, and chlorine-derived products contribute more than $46 billion to the US economy annually. Chlorine plays a major role in many applications such as clean drinking water, pharmaceuticals, and crop protection chemicals. Most chlorine is produced from electrolysis of brine1. Chlorine can also be produced from hydrochloric acid by electrolysis. There are two primary techniques to recycle HCl to Cl2 via electrolysis--a diaphragm cell, which has the advantage of generating H2 as the product, and Proton Exchange Membrane (PEM) electrolyzer, which has the benefit of a higher conversion rate and lower energy consumption2,3. PEM electrolyzers are limited by the Nafion membrane separator, which requires hydration to conduct protons efficiently and is limited to temperatures of ≤ 120 °C. para-Polybenzimidazole (PBI; brand name Celtec-P) membranes are known as high temperature (T ≤ 230 °C) polymer separators that do not require hydration to maintain efficient proton conductivity and can operate in strong acid conditions4–6. In this work, we demonstrate a completely anhydrous HCl electrolysis system using a Celtec-P membrane that operates at temperatures up to 160 °C and has apparent conversion efficiencies up to 93% at 1.8V. We also discuss the results of an experimentally validated computational fluid dynamics (CFD) model and how this model can be used to elucidate and overcome potential electrolyzer limitations. Reference Pamphlet 1 Chlorine Basic, 8th ed., p. 62, The Chlorine Institute, (2014). Industrial Solutions HCl Electrolysis Chlorine Recovery for Greater Sustainability. Thyssenkrupp AG. Accessed December 20, 2021. https://ucpcdn.thyssenkrupp.com/_legacy/UCPthyssenkruppBAISUhdeChlorineEngineers/assets.files/products/hydrochloric_acid_recycling/thyssenkrupp_hcl_electrolysis_brochure_web_1.pdf. “Industrial Technologies Program: Advance Chlor-Alkali Technology.” Office of Energy Efficiency and Renewable Energy,U.S. Department of Energy, January 2006. https://www1.eere.energy.gov/manufacturing/industries_technologies/imf/pdfs/1797_advanced_chlor-alkali.pdf. T. R. Garrick et al., J. Electrochem. Soc., 164, F1591–F1595 (2017). L. Xiao et al., Chem. Mater., 17, 5328–5333 (2005). J. A. Mader and B. C. Benicewicz, Macromolecules, 43, 6706–6715 (2010).

No abstract

There exists a significant and growing need for clean, efficient, and large-scale hydrogen production. Using high temperature heat, thermochemical cycles can provide an energy-efficient route for hydrogen production. The Hybrid Sulfur process is a promising thermochemical watersplitting cycle with global-scale hydrogen production potential. The SO2-depolarized electrolyzer (SDE) is a critical component of the cycle. At the core of the electrolyzer is the membraneelectrode assembly, which consists of a solid electrolyte membrane sandwiched between two electrocatalyst layers. New electrocatalyst and membrane materials are being developed with the goals of improving the electrolyzer performance and extending the lifetime of the membrane-electrode assembly. A high-throughput methodology is being developed to screen potential candidates based on Pt and Au thin films prepared through physical vapor deposition. SO2 oxidation reaction kinetics are being analyzed for the novel catalysts and compared to the state-of-the-art, Pt/C. In addition, advanced polymer electrolyte membranes of polybenzimidazole (PBI) are utilized, which have shown superior performance in comparison to the state-of-the-art, Nafion®. These catalysts and membranes will be combined to produce high performance membrane-electrode assemblies. Awards and Recognition DOE-EERE CRADA awarded Intellectual Property ReviewThis report has been reviewed by SRNL Legal Counsel for intellectual property considerations and is approved to be publicly published in its current form.