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DOE OSTI2023

Mechanistic Insights on Permeation of Water over Iron Cations in Nanoporous Silicon Oxide Films for Selective H 2 and O 2 Evolution

Electrocatalysts encapsulated by an ultrathin and semipermeable oxide layer offer a promising avenue for efficient, selective, and cost-effective production of hydrogen through photoelectrochemical water splitting. This architecture is especially attractive for Z-scheme water splitting, for which a nanoporous oxide film can be leveraged to mitigate undesired, yet kinetically facile, reactions involving redox shuttles, such as aqueous iron cations, by limiting transport of these species to catalytically active sites. In this work, molecular dynamics simulations were combined with electrochemical measurements to provide a mechanistic understanding of permeation of water and Fe(III)/Fe(II) redox shuttles through nanoporous SiO 2 films. It is shown that even for SiO 2 pores with a width as small as 0.8 nm, water does not experience any energy barrier for permeating into the pores due to a favorable interaction with hydrophilic silanol groups on the oxide surface. In contrast, permeation of Fe(III) and Fe(II) into microporous SiO 2 pores is limited due to high energy barriers, which stem from a combination of distortion and dehydration of the second and third ion solvation shells. Furthermore, our simulations and experimental results show that SiO 2 coatings can effectively mitigate undesired Fe(III)/Fe(II) redox reactions at underlying electrodes by attenuating permeation of iron cations, while allowing water to permeate and thus participate in water splitting reactions. In a broader context, our study demonstrates that selectivity of solvated cations can be manipulated by controlling the pore size and surface chemistry of oxide films.

14 SOLAR ENERGY↗

DOE OSTI2020

Microstructural Evolution and ORR Activity of Nanocolumnar Platinum Thin Films with Different Mass Loadings Grown by High Pressure Sputtering

Nanocolumnar platinum thin films (Pt-TFs) with different Pt mass loadings were grown by high pressure sputtering (HIPS) and investigated as oxygen reduction reaction (ORR) electrocatalysts for polymer electrolyte membrane fuel cell applications. Mass loading was controlled by changing the sputter deposition time. A cauliflower-like columnar microstructure was achieved by depositing the Pt-TFs onto a microporous layer (MPL)-like surface composed of carbon particles in order to mimic catalyst-coated gas diffusion electrodes. Microstructural evolution of HIPS Pt-TFs and their ORR activity were investigated. Electrochemical characterization of the nanocolumnar Pt-TFs was performed by cyclic voltammetry and rotating disk electrode measurements on Pt-TF/MPL-like-layer/glassy-carbon samples in an aqueous perchloric acid electrolyte. The electrochemically active surface area increased from 18 to 39 m 2 g –1 as the Pt mass loading was decreased. Specific activity of the films was similar (~600 μA cm –2 ) for all Pt mass loadings, due to the similar nanoparticle sizes of ~5 nm as observed by transmission electron microscopy and X-ray diffraction. Furthermore, mass activity of the films increased from 0.11 to 0.26 A mg –1 as the Pt mass loading was decreased, which is an indication of the effective Pt utilization and better access through the catalyst layer at lower Pt mass loadings.

08 HYDROGEN↗

DOE OSTI2021

Pure- and mixed-gas transport properties of a microporous Tröger's Base polymer (PIM-EA-TB)

Polymers of intrinsic microporosity (PIMs) offer tantalizing combinations of high selectivity and permeability in initial gas permeation measurements. Here, we report characterization of pure- and mixed-gas permeation properties of a thick (~80 μm) PIM consisting of Tröger's Base (TB) and Ethanoanthracene (EA) films. The effects of feed pressure and temperature on pure-gas permeabilities of CH 4 , N 2 , O 2 , H 2 , and CO 2 were investigated. The physical aging behavior of the thick film was tracked via pure-gas O 2 , N 2 , and CH 4 permeability at 35 °C. Gas permeability decreased noticeably and selectivity increased as aging time increased. Particular attention was given to mixed-gas measurements of CO 2 and CH 4 (50/50) permeabilities at 35 °C and fugacities ranging from 2 to 18 atm to explore whether the rigid, bridged, bicyclic TB and EA units could resist CO 2 -induced plasticization. These results are presented along with pure-gas CO 2 and CH 4 results for membrane samples aged at different times. PIM-EA-TB aged for ~24 h did not show signs of plasticization across the fugacity range considered. Furthermore, dual-mode competitive sorption presumably caused the CO 2 /CH 4 mixed-gas selectivity to be slightly higher than its corresponding pure-gas selectivity. However, as aging time increased, aged films underwent progressively more rapid and extensive CO 2 -induced plasticization with increasing fugacity, suggesting a systematic relationship between physical aging and plasticization in PIMs. Consequently, physical aging caused less improvement in mixed-gas CO 2 /CH 4 selectivity than it did in pure-gas selectivity, due mainly to plasticization effects.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS2009

Fabrication and Testing of a Thin-Film Heat Flux Sensor for a Stirling Convertor

The NASA Glenn Research Center (GRC) has been testing high efficiency free-piston Stirling convertors for potential use in radioisotope power systems since 1999. Stirling convertors are being operated for many years to demonstrate a radioisotope power system capable of providing reliable power for potential multi-year missions. Techniques used to monitor the convertors for change in performance include measurements of temperature, pressure, energy addition, and energy rejection. Micro-porous bulk insulation is used in the Stirling convertor test set up to minimize the loss of thermal energy from the electric heat source to the environment. The insulation is characterized before extended operation, enabling correlation of the net thermal energy addition to the convertor. Aging microporous bulk insulation changes insulation efficiency, introducing errors in the correlation for net thermal energy addition. A thin-mm heat flux sensor was designed and fabricated to directly measure the net thermal energy addition to the Stirling convertor. The fabrication techniques include slip casting and using Physical Vapor Deposition (PVD). One micron thick noble metal thermocouples measure temperature on the surface of an Alumina ceramic disc and heat flux is calculated. Fabrication, integration, and test results of a thin film heat flux sensor are presented.

Wilson, Scott D.↗

DOE OSTI2025

Creation of Self-Semi-Interpenetrating Network Structures in PIM-1 Membranes for Enhanced Physical Aging Resistance

A series of self-semi-interpenetrating network (ssIPN) thin films based on PIM-1 structure were developed by end-cross-linking telechelic PIM-1 oligomers end-capped with curable carboxylic acid groups to form model networks, which are penetrated by linear high-molecular-weight PIM-1 chains. ssIPN films with systematically varied network content ranging from 10 to 30 wt % were comprehensively examined on their microstructure and gas permeation properties. Fresh PIM-1 ssIPN films exhibited gas separation performances close to those of as-cast linear PIM-1, where the films closely followed the upper bound trade-off line, gaining as much selectivity as they lose gas permeability as the network content increases. This indicates that gas permeability is largely preserved despite cross-linking. Wide-angle X-ray scattering supported this observation, with peaks shifting toward lower d-spacing as oligomer content increased, suggesting tighter chain packing with higher cross-linkable oligomer loading. In physical aging studies over two months, all ssIPN films outperform linear PIM-1 for H 2 /CH 4 and O 2 /N 2 separations. Notably, the PIM-1 ssIPN with 10 wt % network content showed the best physical aging resistance, with negligible permeability loss even after one month. Finally, these findings highlight a promising macromolecular strategy for enhancing the physical aging resistance of microporous polymer membranes for gas separation.

PIM-1↗

DOE OSTI2026

Polymer-Derived Amorphous Aluminosilicate Nanomembranes for H 2 Purification

Aluminosilicate zeolite membranes with robust microporous crystalline structures are attractive for the molecular separation of H 2 from light gases, but their large-scale fabrication is complicated and costly, hindering their practical applications. Herein, we present polymer-derived amorphous aluminosilicate nanomembranes that combine the exceptional processability of polymers with the superior gas separation properties of aluminosilicates. Specifically, thin-film composite membranes comprising 150 nm polydimethylsiloxane were first treated with oxygen plasma to generate 10 nm polyorganosilica (POSi) on the surface, which were then subjected to few-cycle atomic layer deposition (ALD) using trimethylaluminum as a metal precursor and water vapor as a coreactant. This scalable two-step process yields few-nanometer amorphous aluminosilicates with strong size-sieving ability. For example, three-cycle ALD treatment of POSi increases H 2 /CO 2 selectivity from 39 to 200 and H 2 /CH 4 selectivity from 190 to 500, while decreasing H 2 permeance from 990 to 210 GPU at 150 °C, superior to the state-of-the-art membranes. In conclusion, rapid and scalable manufacturing of amorphous aluminosilicate nanolayers can also be of interest for catalysis and adsorption applications.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Sequential Infiltration Synthesis of Bilayer Porous Alumina Nanostructures for Broad-Angle, Broadband Antireflective Coatings

Antireflective coatings (ARCs) are thin films engineered to reduce light reflections. Delivering broadband, wide-angle performance is essential for photovoltaics, imaging, and sensing, yet truly omnidirectional antireflection remains difficult due to angle-dependent optical paths and a narrow palette of suitable refractive indices. Here, in this study, we systematically investigate an emerging class of multilayer inorganic ARCs based on conformally coated nanoporous alumina templated by intrinsically microporous polymers (PIMs) and block copolymers (BCPs). We establish a design framework that maps thickness reflectance relationships to identify thickness pairs minimizing reflection across wavelength and incidence angle. We show that deliberately separating the local reflectance minima of the top and bottom layers in bilayer nanostructures broadens the antireflective bandwidth and angular range. We show that 235-nm single-side bilayer porous alumina nanostructures achieves under 2 % reflectance from 380–750 nm for incidence angles up to 45° with less than 0.6% reflectance for incidence angles under 20°. The approach is readily extensible to additional layers or materials with refractive indices tuned via templated nanoporosity and composition, enabling practical, etch-free ARC fabrication without HF or fluorinated precursors and advancing straightforward design of broadband, wide-angle (quasi-omnidirectional) ARCs for next-generation optical systems.

antireflective coatings↗

DOE OSTI2024

Regioisomeric Spirobifluorene CANAL Ladder Polymers and Their Gas Separation Performance

For this work, we synthesized and characterized two isomeric microporous hydrocarbon ladder polymers from catalytic arene norbornene annulation (CANAL) of regioisomeric bis-norbornene fused spirobifluorenes, where the ladder chains are connected either through the same fluorene unit or across two different fluorene units in spirobifluorene. This pair of isomeric polymers was used to investigate the effect of ladder macromolecular structures on the microporosity and transport properties. Both polymers form mechanically intact films with thermal stability up to 480 °C and relatively high BET surface areas. The polymer formed from 2,7-dibromospirobifluorene showed higher BET surface area and higher gas permeability than the polymer from 2,2'-dibromospirobifluorene despite similar intersegmental spacing as indicated by X-ray scattering. The aging behavior for both polymers followed the same trend as the previously reported CANAL-fluorene polymers, with dramatically increased permselectivities over time, resulting in gas separation performance above the 2008 upper bounds for H 2 /CH 4 and O 2 /N 2 .

36 MATERIALS SCIENCE↗

DOE OSTI2023

Structure–Transport Relationships of Water–Organic Solvent Co-transport in Carbon Molecular Sieve (CMS) Membranes

We explore the effects of the carbon molecular sieve (CMS) microstructure on the separation performance and transport mechanism of water–organic mixtures. Specifically, we utilize PIM-1 dense films and integrally skinned asymmetric hollow fiber membranes as polymer precursors for the CMS materials. The PIM-1 membranes were pyrolyzed under several different pyrolysis atmospheres (argon, carbon dioxide, and diluted hydrogen gas) and at multiple pyrolysis temperatures. Detailed gas physisorption measurements reveal that membranes pyrolyzed under 4% H 2 and CO 2 had broadened ultramicropore distributions (pore diameter <7 Å) compared to Ar pyrolysis, and pyrolysis under CO 2 increased ultramicropore volume and broadened micropore distributions at increased pyrolysis temperatures. Gravimetric water and p-xylene sorption and diffusion measurements reveal that the PIM-1-derived CMS materials are more hydrophilic than other CMS materials that have been previously studied, which leads to sorption-diffusion estimations showing water-selective permeation. Water permeation in the vapor phase, pervaporation, and liquid-phase hydraulic permeation reveal that the isobaric permeation modes (vapor permeation and pervaporation) are reasonably well predicted by the sorption-diffusion model, whereas the hydraulic permeation mode is significantly underpredicted (>250×). Conversely, the permeation of p-xylene is well predicted by the sorption-diffusion model in all cases. The collection of pore size analysis, vapor sorption and diffusion, and permeation in different modalities creates a picture of a combined transport mechanism in which water–under high transmembrane pressures–permeates via a Poiseuille-style mechanism, whereas p-xylene solutes in the mixture permeate via sorption-diffusion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Influence of Ink Formulation and Drying Conditions on Ionomer Distribution in High-Performance Roll-to-Roll-Coated Gas-Diffusion Electrodes

To enable mass production of fuel cell membrane electrode assemblies (MEAs) catalyst layers production will require continuous roll-to-roll (R2R) coating processes. Gas diffusion electrodes (GDEs) are advantageous for mass production because the catalyst layer can be directely coated on the microporous layer of the gas diffusion media without the need for a decal-transfer process. It is known that the water-to-alcohol ratio in the catalyst ink influences the interactions of the ionomer with the catalyst leading to different distributions of ionomer in spray-coated catalyst layers. It is also known that during drying of colloidal mixtures, like fuel cell inks, factors such as drying rate, particle size, and agglomeration influence how the materials distribute themselves throughout the thickness of the dired film. Thus far there have only been limited studies to understand how process conditions such as ink formulation and drying temperature influence the distribution of ionomer and catalyst coated using scalable methods. This understanding is especially important for GDEs since it is known that having a sufficient amount of ionomer at the catalyst layer-membrane interface is critical for high performance. In this study we have focused on determining how the ratio of water to 1-propanol in the catalyst ink ink and drying temperature influence the distribution of ionomer throughout the thickness of the catalyst layer. Using a combination of Kelvin probe and x-ray photoelectron spectroscopy we show that an ionomer-rich surface is promoted by a higher drying rate and a water-rich catalyst ink. In contrast, a 1-propanol catalyst ink leads to a lower concentration of ionomer on the top surface. Using x-ray computed tomography, we are able to characterize the ionomer distribution throughout the thickness of the layer. We find that, in addition to promoting an ionomer-rich top surface, water-rich inks lead to a more homogenous distribution of ionomer, whereas a 1-propanol-rich ink leads to a more irregular distribution. It is found that MEA performance is improved by selecting conditions and ink formulations that promote ionomer enrichment at the top surface to facilitate a good interface with the membrane. MEAs prepared with a 75 wt% water catalyst ink with a 0.9 I/C have equivalent performance to spray-coated GDEs. Critically, these R2R-coated GDEs do not need an additional ionomer overlayer like the spray-coated GDEs do, reducing the number of processing steps in a manufacturing setting. This work shows that with the appropriate selection of materials, ink formulation, and processing conditions gas-diffusion electrodes are a viable pathway for fuel cell manufacturing.

ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION↗

DOE OSTI2024

Stable water splitting using photoelectrodes with a cryogelated overlayer

Hydrogen production techniques based on solar-water splitting have emerged as carbon-free energy systems. Many researchers have developed highly efficient thin-film photoelectrochemical (PEC) devices made of low-cost and earth-abundant materials. However, solar water splitting systems suffer from short lifetimes due to catalyst instability that is attributed to both chemical dissolution and mechanical stress produced by hydrogen bubbles. A recent study found that the nanoporous hydrogel could prevent the structural degradation of the PEC devices. In this study, we investigate the protection mechanism of the hydrogel-based overlayer by engineering its porous structure using the cryogelation technique. Tests for cryogel overlayers with varied pore structures, such as disconnected micropores, interconnected micropores, and surface macropores, reveal that the hydrogen gas trapped in the cryogel protector reduce shear stress at the catalyst surface by providing bubble nucleation sites. The cryogelated overlayer effectively preserves the uniformly distributed platinum catalyst particles on the device surface for over 200 h. Our finding can help establish semi-permanent photoelectrochemical devices to realize a carbon-free society.

42 ENGINEERING↗

DOE OSTI2020

Engineering Surface Oxygenated Functionalities on Commercial Carbon toward Ultrafast Sodium Storage in Ether-Based Electrolytes

The pursuit of a high-capacity anode material has been urgently required for commercializing sodium-ion batteries with a high energy density and an improved working safety. In the absence of thermodynamically stable sodium intercalated compounds with graphite, constructing nanostructures with expanded interlayer distances is still the mainstream option for developing high-performance carbonaceous anodes. In this regard, a surface-functionalized and pore-forming strategy through a facile CO 2 thermal etching route was rationally adopted to engineer negligible oxygenated functionalities on commercial carbon for boosting the sodium storage process. Benefitted from the abundant ionic/electronic pathways and more active reaction sites in the microporous structure with noticeable pseudocapacitive behaviors, the functionalized porous carbon could achieve a highly reversible capacity of 505 mA h g -1 at 50 mA g -1 , an excellent rate performance of 181 mA h g -1 at 16,000 mA g -1 , and an exceptional rate cycle stability of 176 mA h g -1 at 3200 mA g -1 over 1000 cycles. These outstanding electrochemical properties should be ascribed to a synergistic mechanism, fully utilizing the graphitic and amorphous structures for synchronous intercalations of sodium ions and solvated sodium ion compounds, respectively. Finally, the controllable generation and evolution of a robust but thin solid electrolyte interphase film with the emergence of obvious capacitive reactions on the defective surface, favoring the rapid migration of sodium ions and solvated species, also contribute to a remarkable electrochemical performance of this porous carbon black.

25 ENERGY STORAGE↗

DOE OSTI2025

Microporous pentiptycene-based polybenzimidazole membranes for high temperature H 2 /CO 2 separation

Separating H 2 from syngas at elevated temperatures (100–250 °C) have attracted significant attention in recent years as a means to reduce energy consumption and capital costs in precombustion carbon capture processes, such as those following steam reforming of natural gas or coal gasification. Polybenzimidazole (PBI), particularly m-PBI, has been reported as a leading membrane material for high-temperature H 2 /CO 2 separation. However, m-PBI exhibits extremely low H 2 permeability, even at high temperatures, which limits its productivity in H 2 /CO 2 separation applications. Here, to address this limitation, this work introduces a new pentiptycene-based polybenzimidazole (PPBI) featuring significantly enhanced H 2 permeability and attractive high-temperature H 2 /CO 2 separation performance, which stems from the unique configurational free volume elements introduced by pentiptycene moieties. Further tuning of the free volume architecture of PPBI films is achieved via acid doping with phosphoric acid (PA) or trans-aconitic acid (TaA), which introduces crosslinking among PPBI chains. Under mixed-gas environment (50/50 mol% H 2 /CO 2 ) at 180 °C, the acid-doped PPBI films exhibit a ∼230 % increase in H 2 /CO 2 selectivity compared to pristine PPBI film while maintaining high H 2 permeability that is nearly 500 % of m-PBI. These properties approach the predicted upper bound for membrane operating at 180 °C, highlighting its great potential for high-temperature H 2 /CO 2 separation.

Liu, Mengdi [University of Notre Dame, IN (United ↗

NASA NTRS1988

Electronic materials high-T(sub c) superconductivity polymers and composites structural materials surface science and catalysts industry participation

The fifth year of the Center for Advanced Materials was marked primarily by the significant scientific accomplishments of the research programs. The Electronics Materials program continued its work on the growth and characterization of gallium arsenide crystals, and the development of theories to understand the nature and distribution of defects in the crystals. The High Tc Superconductivity Program continued to make significant contributions to the field in theoretical and experimental work on both bulk materials and thin films and devices. The Ceramic Processing group developed a new technique for cladding YBCO superconductors for high current applications in work with the Electric Power Research Institute. The Polymers and Composites program published a number of important studies involving atomistic simulations of polymer surfaces with excellent correlations to experimental results. The new Enzymatic Synthesis of Materials project produced its first fluorinated polymers and successfully began engineering enzymes designed for materials synthesis. The structural Materials Program continued work on novel alloys, development of processing methods for advanced ceramics, and characterization of mechanical properties of these materials, including the newly documented characterization of cyclic fatigue crack propagation behavior in toughened ceramics. Finally, the Surface Science and Catalysis program made significant contributions to the understanding of microporous catalysts and the nature of surface structures and interface compounds.

Source record↗

DOE OSTI2022

One-step fabrication of robust lithium ion battery separators by polymerization-induced phase separation

Conventional lithium ion battery separators are microporous polyolefin membranes that play a passive role in the electrochemical cell. Next generation separators should offer significant performance enhancements, while being fabricated through facile, low cost approaches with the ability to readily tune physicochemical properties. This study presents a single-step manufacturing technique based on UV-initiated polymerization-induced phase separation (PIPS), wherein microporous separators are fabricated from multifunctional monomers and ethylene carbonate (EC), which functions as both the pore-forming agent (porogen) and electrolyte component in the electrochemical cell. By controlling the ratio of the 1,4-butanediol diacrylate (BDDA) monomer to ethylene carbonate, monolithic microporous membranes are readily prepared with 25 μm thickness and pore sizes and porosities ranging from 6.8 to 22 nm and 15.4% to 38.5%, respectively. With 38.5% apparent porosity and an average pore size of 22 nm, the poly(1,4-butanediol diacrylate) (pBDDA) separator takes up 127% liquid electrolyte, resulting in an ionic conductivity of 1.98 mS cm –1 , which is greater than in conventional Celgard 2500. Lithium ion battery half cells consisting of LiNi 0.5 Mn 0.3 Co 0.2 O 2 cathodes and pBDDA separators were shown to undergo reversible charge/discharge cycling with an average discharge capacity of 142 mA h g –1 and a capacity retention of 98.4% over 100 cycles – comparable to cells using state-of-the-art separators. Moreover, similar discharge capacities were achieved in rate performance tests due to the high ionic conductivity and electrolyte uptake of the film. Finally, the pBDDA separators were shown to be thermally stable to 374 °C, lack low temperature thermal transitions that can compromise cell safety, and exhibit no thermal shrinkage up to 150 °C.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗