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Kushner, Douglas I.

Publications and source records attributed to Kushner, Douglas I..

14 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Pathways Toward Efficient and Durable Anion Exchange Membrane Water Electrolyzers Enabled By Electro‐Active Porous Transport Layers

Abstract Green hydrogen, produced via water electrolysis using renewable electricity, will play a crucial role in decarbonizing industrial and heavy‐duty transportation sectors. Anion exchange membrane water electrolyzers (AEMWEs) can overcome many of the performance and cost limitations of incumbent technologies, however, still suffer from durability challenges due to oxidative instability of anion‐exchange ionomers. Herein, the use of an electro‐active porous transport layer as anode (PTL‐electrode) is demonstrated to enable efficient and durable AEMWEs. The stainless‐steel PTL‐electrodes are shown to have superior performance and durability compared to traditional catalyst layers containing ionomer and nanoparticle catalysts. An AEMWE cell operating at 2 A cm −2 for over 600 h exhibited a degradation rate of just 5 µV h −1 . During operation, the surface composition of the stainless steel transforms into a mixture of iron and nickel oxyhydroxides, contributing to enhanced oxygen‐evolution reaction activity. The combination of experimental work and modeling elucidates how the bulk structure of the PTL‐electrode offers an additional design dimension to further improve electrolyzer performance. Lastly, a surface modification strategy is applied to a PTL‐electrode to achieve an even higher performing AEMWE (2.3 vs 2.0 A cm −2 at 1.8 V). Overall, this work lays out pathways toward more efficient, durable, and affordable AEMWEs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Exploring Proton Activity at the Membrane/Electrode Interface with Microelectrodes

Microelectrode measurements using a polycrystalline platinum microelectrode were used to simulate the membrane/electrode interface of a membrane-electrode-assembly (MEA) architecture. The proton activity for the hydrogen-evolution reaction (HER) was evaluated for 40, 60, and 80% relative humidity. Proton activity was calculated to be 0.5, 1.0 and 2.0 for 40, 60, and 80% relative humidity, respectively, using open circuit potential measurements between Nafion 211 and 1 molal HClO 4 . The fraction of protons which dissociate at a given relative humidity condition appears to be a distinctive factor in proton activity for Nafion 211 compared to an aqueous electrolyte. In conclusion, the microelectrode measurements exhibited a Tafel slope of ~120 mV/dec, similar to that observed for platinum in MEA systems, demonstrating that kinetic measurements made with microelectrodes can be representative of MEA kinetics.

Anderson, Grace C.↗
DOE OSTI2023

Anion exchange membranes: The effect of reinforcement in water and electrolyte

Alkaline anion-conducting polymer-based CO 2 electrolysis and water electrolysis are among two emerging renewable energy conversion technologies. Their system design and integration offer promise of lower capital cost due to utilization of low-cost catalysts, in contrast to platinum group metal catalysts required for cation-conducting polymer-based devices. However, a critical component, the polymer electrolyte membrane, remains an obstacle hampering system performance and durability. In this study, commercially-available Sustainion® membranes with and without PTFE-reinforcement were investigated to understand previously unreported origins of improved device performance when compared to alternative membrane chemistries. We report critical membrane properties, such as morphology, thermal stability, as well as temperature-, hydration-, and counter-ion dependent ion conductivity. Moveover, the changes in uptake and conductivity of membranes in supporting electrolytes of K 2 CO 3 and KOH investigated as a function of their concentration. Presence of reinforcement and supporting electrolyte type alter the membrane's transport functionality, which could help guide device design for improved performance. In conclusion, the obtained results not only show how Sustainion® properties change with operating environment for CO 2 and water electrolysis applications, but also provide understanding for internal and external factors controlling anion-exhcnage membrane functionality in electrochemical devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Anion Exchange Ionomers: Impact of Chemistry on Thin-Film Properties

Ionomer thin-films (i.e., 20–100 nm) on supports serve as model systems to understand ionomer-catalyst interfacial behavior as well as the confinement-driven deviation in properties from bulk membranes. While ionomer thin-films have been examined for proton exchange ionomers, the thin-film properties of anion exchange ionomers (AEIs) remain largely unexplored. More importantly, delineating the convoluted impact of chemistry and confinement on thin-film morphology and hydration is of interest to advancing the field on functional ionic interfaces. In this work, these aspects are studied by using AEIs of different backbones (perfluorinated, aliphatic, and aromatic) and side chains (various lengths, and single versus dual functional groups). Quartz-crystal microbalance and spectroscopic ellipsometry are used to analyze density and coupled with calculated free volume fraction of thin-films to provide insights on their gas transport properties. AEI side-chain's chemical character plays a key role in how confinement modulates hydration (in thin-film versus bulk). Overall, the results elucidate the effects of backbone, side-chain chemistry versus anion/cation type in the confinement-driven changes in thin-film morphology and swelling. This study also provides new insights for tuning AEI transport functionalities at interfaces via chemistry, which can benefit the design and development of electrode-ionomers for alkaline membrane-based energy systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Supported Oxygen Evolution Catalysts by Design: Toward Lower Precious Metal Loading and Improved Conductivity in Proton Exchange Membrane Water Electrolyzers

Reducing the precious metal content of water oxidation catalysts for proton-exchange-membrane water electrolyzers remains a critical barrier to their large-scale deployment. Herein, we present an engineered architecture for supported iridium catalysts, which enables decreased precious metal content and improved activity and conductivity. The improvement in performance at lower precious metal loading is realized by the deposition of a conformal layer of platinum nanoparticles on titanium dioxide (TiO 2 ) using a facile photoreduction method to prepare conductive layer coated supports (CCSs). Platinum nanoparticles are homogeneously dispersed on TiO 2 , and the conductivity of the subsequent catalysts with 39 wt % precious group metal loadings is significantly higher than the commercial 75 wt % loaded IrO 2 -TiO 2 catalysts. The conformal conductive layer also maintains an enhanced conductivity and electrochemical activity upon thermal annealing when compared to catalysts without the conductive layer and nonconformal heterogeneous conductive layer. The iridium mass activity from half-cell studies shows a 141% improvement for CCS supported catalysts at 42% lower loadings compared to the commercial catalysts. The conductive layer also improves the single cell electrolyzer performance at a similar catalyst loading in comparison to a commercial state-of-the-art catalyst. Here, we correlate the physical properties of the engineered catalysts with their electrochemical performance in electrolyzers to understand structure-activity relationships, and we anticipate further performance improvements upon synthesis and materials optimizations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Substrate‐Dependent Molecular and Nanostructural Orientation of Nafion Thin Films

Abstract The effects of film thickness and substrate composition on the ionomer structure in porous electrodes are critical in understanding pathways toward developing higher performance electrochemical devices, including fuel cells and batteries. Insights are gained into the molecular and nanostructural orientation dependence for thin Nafion films (12–300 nm thick) on gold, platinum, and SiO 2 model substrates. Molecular orientation is determined from the birefringence measured using spectroscopic ellipsometry, while the nanostructural orientation of the ionic domains is measured using grazing‐incidence small‐angle X‐ray scattering. Density functional theory calculations for the molecular polarizability of the Nafion backbone and side chain show complimentary contributions to the measured birefringence values for the material. Nafion films prepared on SiO 2 substrates exhibit a nearly isotropic molecular and nanostructural orientation. Films on gold and platinum display parallel backbone orientations, relative to the substrate, with decreasing film thickness. However, a birefringence transition toward molecular isotropy is observed for 30 nm thick films on Au and Pt; while the ionic nanostructured domains continuously align parallel to the substrate. This apparent isotropic molecular orientation with increasing domain orientation highlights the difference between the backbone and side chain orientation, a key finding for elucidating transport in confined films at the interfaces.

Kushner, Douglas I.↗
DOE OSTI2019

Mass-Transport Resistances of Acid and Alkaline Ionomer Layers: A Microelectrode Study Part 1 - Microelectrode Development

The use of microelectrodes to study localized mass-transport phenomena in fuel-cell catalyst layers is an increasingly valuable tool. However, existing microelectrode cells have been used in static, equilibrated environment modes with poorly controlled interfaces. In this work, we present a microelectrode cell design that expands the experimental space addressable by microelectrodes to include mechanical pressure, gas flow and ionomer medium, and experimental throughput. The feasibility of the design is examined for fuel-cell reactions, with oxygen reduction currents independent of mechanical pressure and gas flowrate. Finally, cell equilibration time and IR drop across the electrolyte are estimated. The new cell design is robust and provides a consistent base from which to perform more complicated studies examining mass-transport properties of ionomers and/or the electrochemical reaction kinetics of hydrogen oxidation and oxygen reduction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Poly(olefin)-Based Anion Exchange Membranes Prepared Using Ziegler–Natta Polymerization

Bromoalkyl-functionalized poly(olefin)s were synthesized by copolymerization of 4-(4-methylphenyl)-1-butene with 11-bromo-1-undecene using Ziegler–Natta polymerization. The resulting bromoalkyl-functionalized poly(olefin)s were converted to quaternary ammonium-containing anion-conductive copolymers by reacting the pendant bromoalkyl group with trimethylamine or a custom-synthesized tertiary amine containing pendant quaternary ammonium moieties. Poly(olefin)-based AEMs with three cations per side chain showed considerably higher hydroxide conductivities, up to 201 mS/cm at 80 °C in liquid water, compared to that of samples with only one cation per bromoalkyl site (68 mS/cm, 80 °C, liquid water), likely due to phase separation in the triple-cation structure. More importantly, triple-cation side-chain poly(olefin) AEMs exhibited higher hydroxide conductivity under relative humidity conditions (50%–100%) than typical AEMs based on benzyltrimethylammonium cations. Here, the triple-cation the triple-cation side-chain poly(olefin)-based AEM exhibited an ionic conductivity as high as 115 mS/cm under 95% RH at 80 °C and 11 mS/cm under 50% RH at 80 °C. In addition to high ionic conductivity, the triple-cation side-chain poly(olefin) AEMs exhibited good chemical and dimensional stability. High retention of ionic conductivity (>85%) was observed for the samples in 1 M NaOH at 80 °C over 1000 h. Based on these high-performance poly(olefin) AEMs, a fuel cell with a peak power density of 0.94 W cm –2 (1.28 W cm –2 after iR correction) was achieved under H 2 /O 2 at 70 °C. The results of this study suggest a new, low-cost, and scalable route for preparation of poly(olefin)-based AEMs for anion exchange membrane applications.

25 ENERGY STORAGE↗
DOE OSTI2019

Interplay between Swelling Kinetics and Nanostructure in Perfluorosulfonic Acid Thin-Films: Role of Hygrothermal Aging

Impacts of processing, storage, and operation on thin-film perfluorosulfonic acid (PFSA) ionomer coatings used in electrodes of electrochemical devices remains unestablished. In this work, alteration of structure–function relationship in ionomers is achieved via exposure to elevated temperature and humidity (hygrothermal aging). Findings reflect a strong inverse correlation between aging-induced ionomer thin-film domain orientation and water-transport kinetics evaluated from swelling. Finally, impact of aging is shown to be more pronounced on platinum due to interactions with PFSA, as evidenced by greater increase in nanodomain orientation parallel to substrate accompanied by reduced water transport, in contrast to silicon support.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Thermal Transitions in Perfluorosulfonated Ionomer Thin-Films

Thin perfluorosulfonated ion-conducting polymers (PFSI ionomers) in energy-conversion devices have limitations in functionality attributed to confinement-driven and surface-dependent interactions. This study highlights the effects of confinement and interface-dependent interactions of PFSI thin-films by exploring thin-film thermal transition temperature (T T ). Change in T T in polymers is an indicator for chain relaxation and mobility with implications on properties like gas transport. Here, this work demonstrates an increase in T T with decreasing PFSI film thickness in acid (H + ) form (from 70 to 130 °C for 400 to 10 nm, respectively). In metal cation (M + ) exchanged PFSI, T T remained constant with thickness. Results point to an interplay between increased chain mobility at the free surface and hindered motion near the rigid substrate interface, which is amplified upon further confinement. This balance is additionally impacted by ionomer intermolecular forces, as strong electrostatic networks within the PFSI-M + matrix raises T T above the mainly hydrogen-bonded PFSI-H + ionomer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Investigation of polymer–solvent interactions in poly(styrene sulfonate) thin films

The swelling behavior of acid form poly(styrene sulfonate) (PSS-H) thin films were investigated using in situ spectroscopic ellipsometry (SE) to probe the polymer–solvent interactions of ion-containing polymers under interfacial confinement. The interaction parameter (χ), related to the polymer and solvent solubility parameters in the Flory–Huggins theory, describes the polymer-solvent compatibility. In situ SE was used to measure the degree of polymer swelling in various solvent vapor environments, to determine χ for the solvent-PSS-H system. The calculated solubility parameter of 40–44 MPa 1/2 for PSS-H was determined through measured χ values in water, methanol, and formamide environments at a solvent vapor activity of 0.95. Flory–Huggins theory was applied to describe the thickness-dependent swelling of PSS-H and to quantify the water-PSS-H interactions. Confinement had a significant influence on polymer swelling at low water vapor activities expressed as an increased χ between the water and polymer with decreasing film thickness. Finally, as the volume fraction of water approached ~0.3, the measured χ value was ~0.65, indicating the water interacted with the polymer in a similar manner, regardless of thicknesses.

36 MATERIALS SCIENCE↗