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  1. Evaluating the Effects of Anode Porous Transport Layer on the Performance and Durability of Anion Exchange Membrane Electrolyzers

    Intikhab, Saad ; Oliveira, Alexandra ; Reeves, Kimberely S. ; ... - ACS Omega
    As anion exchange membrane systems have emerged as a competitive low temperature electrolysis technology, research has expanded to other components and device integration. In this study, nickel (Ni) and stainless steel (SS)-based porous transport layers (PTLs) are investigated in membrane electrode assemblies (MEAs). Compared to MEAs using Ni, the SS PTL shows higher performance due to less kinetics and residual loss and possibly due to a combination of iron mobility improving oxygen evolution reactivity and electron conduction pathways, as well as higher porosity increasing site access. Voltage decay rates of approximately 144 and 115 μV/h, respectively, for the Ni andmore » SS PTLs are found, although the long-term durability and lifetime implications are convoluted. Voltage breakdown analysis confirms that both PTLs saw significant increases in residual loss possibly due to catalyst/PTL property changes that affected electronic, ionic, and mass transport pathways. For the Ni PTL, a higher proportion of the losses were due to cell kinetics; comparatively, more of the SS PTL losses were due to increases in the high frequency resistance. The experimental findings presented here provide insights on the impact of the PTL materials and their properties.« less

  2. Influence of Cellular Redox Reactions on the Structure and Function of Light Harvesting and Photosystems

    Laughlin, Alexander ; Brady, Nathan ; Kisgeropoulos, Effie ; ... - Frontiers in Photobiology
    Photosynthesis enables the conversion of one of the most abundant and free forms of energy, sunlight, into chemical bonds through the utilization of highly tailored protein complexes. These enzymes work in unison to absorb, convert, and transform light into high-energy electrons which are used for various functions important to metabolism and cellular protection. Over the last ~50 years, photosynthetic organisms, such as cyanobacteria, have been adapted and engineered to produce valuable compounds like hydrogen and ethylene, among others. Often this is performed by removing native and/or adding in exogenous energy utilization pathways so that light energy is re-directed towards themore » synthesis of desired compounds. However, the interplay between primary light capture, conversion reactions, and the downstream electron utilization sinks is not fully understood. Further complicating these strategies are the plethora of compensatory mechanisms that facilitate steady electron flow and the maintenance of photosynthesis under dynamic conditions. This manifests as structural and functional plasticity of the photosynthetic machinery, often seen in modulations of oligomeric compositions or changes in protein-protein interactions and coupling with redox enzymes. Understanding these mechanisms is crucial to biotechnology applications because re-engineering electron utilization sinks has profoundly different effects on the light capture and conversion reactions of photosynthesis. Optimization requires a molecular-level understanding of the functional interrelationships between electron sinks and photosynthetic components that influence photosynthetic efficiencies to realize potential improvements in product yields. Here, we aim to highlight how perturbation of reductive reactions is revealing the functional plasticity in key components of the photosynthetic energy transduction pathway.« less

  3. Influence of Rigidity–Hydration Coupling on Size-Dependent Diffusion in Hydrated Polymer Membranes

    Irving, Paul R. ; Rane, Soham ; Freeman, Benny D. ; ... - ACS Macro Letters
    Selective ion transport in polymer membranes depends critically on how penetrant motion couples to polymer dynamics and hydration. Yet, the mechanistic interplay between polymer rigidity, water content, and penetrant size remains poorly understood, especially in the regime where the penetrant diameter, polymer Kuhn length, and correlation length are comparable. Here, we employ coarse-grained molecular dynamics simulations to systematically investigate penetrant diffusion in hydrated polymer networks across a broad range of water volume fractions, chain rigidities, and penetrant sizes. The results reveal a transition from a decoupled regime, where small penetrants diffuse nearly independently of polymer relaxation, to a coupled regimemore » in which large penetrants require cooperative polymer motion for transport. Increasing polymer rigidity amplifies the sensitivity of diffusivity to hydration, particularly at low water content, leading to pronounced deviations from Stokes−Einstein scaling. Comparison with scaling theories and free-volume models shows that classical nanoparticle-based frameworks fail to capture this intermediate regime. To address this gap, we extend the Yasuda model to incorporate polymer rigidity through a single parameter that quantifies the dynamic contribution of chain stiffness to free-volume fluctuations. The resulting model collapses diffusivity data across all sizes, water contents, and rigidities, providing a unified description of penetrant transport in hydrated polymer matrices. Furthermore, these findings establish polymer rigidity as a key, tunable determinant of diffusion and offer a framework for interpreting size-dependent transport in ion-selective membranes.« less

  4. Impact of Interposer Microstructure on Ionic Transport in Liquid-Phase Bicarbonate Electrolysis

    Dentzer, Elizabeth ; Kim, Hanwoong ; Zhu, Yaguang ; ... - ACS Electrochemistry
    The electrochemical reduction of CO2 (CO2RR) is a potentially scalable approach for converting captured carbon dioxide into value-added products. Conventional gas-phase electrolysis systems can suffer from carbonate crossover, which limits the efficiency of the system. Liquid-phase (bi)carbonate electrolysis using bipolar membrane electrode assemblies (BPMMEA) has emerged as a promising alternative. The interposer layer, a porous mass-transport material between the BPM and the catalyst, is an essential component of the MEA, as it allows evolved CO2 to reach the catalyst surface for reaction. In the absence of this layer, evolved CO2 generated by the pH swing process at the BPM canmore » be converted back into (bi)carbonate (CO2 recapture) due to the high bulk pH. Thus, clear design guidelines are needed to maximize CO2 conversion, minimize CO2 recapture in the catholyte, and improve energy efficiency. Here, the transport properties of the interposer are systematically characterized by X-ray tomography and symmetric-cell impedance spectroscopy to quantify porosity, tortuosity, and the resulting MacMullin number. We then examine the correlation between these material properties and the electrolyzer performance. We focus on characterizing two commercial porous membrane filters, mixed cellulose ester (MCE) and poly(ether sulfone) (PES).« less

  5. An Acid-Free, Temperature-Based Cation Contamination Removal Strategy for PEM Water Electrolysis

    Li, Siqi ; Wrubel, Jacob ; Blair, Sarah ; ... - Journal of the Electrochemical Society
    It is widely understood that the durability and reliability of polymer electrolyte membrane (PEM) water electrolyzers are heavily dependent on feedwater purity, with cation contaminants that originate from incomplete water purification and balance of plant materials significantly harming electrolyzer performance. However, contamination remains a challenge and a common cause of failure at the stack level, indicating the need for strategies to recover the performance of contaminated cells. In this study, we investigate the effects of temperature on the uptake, electrochemical impacts, and removal of contaminant calcium and iron cations. Lower operating temperatures increase the sensitivity of the cell performance tomore » contaminant cations, while also decreasing cation uptake and promoting contaminant removal. Computational charge transfer modelling shows that lower temperature increases the concentration of contaminant at the cathode and facilitates their removal from the cell. By testing single cells under scenarios designed to mimic stack temperature dynamics, we investigate low-temperature operation as an approach to stack-relevant contaminant recovery. Together, these results demonstrate that the low-temperature recovery approach is a promising approach for acid-free contamination recovery for PEM water electrolysis to promote stack reliability and durability.« less

  6. Strain and Defect-Tailored Magnetotransport in NiCo2O4 Thin Films and Freestanding Membranes

    Wu, Qiuchen ; Zhang, Yuanyuan ; Li, Tianlin ; ... - ACS Nano
    Magnetic spinel NiCo2O4 is promising for developing spintronic applications due to its high magnetic Curie temperature, high spin polarization, fast spin dynamics, and strain-tunable magnetic anisotropy, while its electronic and magnetic properties depend sensitively on epitaxial strain and disorder. Here, we use epitaxial NiCo2O4 thin films and freestanding NiCo2O4 membranes as model systems to reveal the complex interplay of strain and defects in determining the metallicity and magnetotransport properties of the ferrimagnetic spinel. NiCo2O4 on perovskite substrates and NiCo2O4 membranes exhibit insulating behaviors and spin canting, in sharp contrast to the metallic NiCo2O4 films on spinel substrates that possess strongmore » perpendicular magnetic anisotropy. Anisotropic magnetoresistance studies provide critical information about disorder-induced spin scattering and strain-induced tetragonal magnetocrystalline anisotropy, which is corroborated by comprehensive electron microscopy characterizations. Here, our study presents a promising venue for designing flexible magnetic memory, sensor, and spintronic applications.« less

  7. Water As a Gas Separation Membrane

    Lopez, Kian ; Saffer-Meng, Max ; Allouzi, Mohammad ; ... - Nature Communications
    Efficient gas separation membranes are essential for carbon capture, biogas upgrading, and hydrogen purification. Inspired by how plants absorb CO2 through water, we present a membrane platform that uses liquid water as the selective layer. Hydrophilic sub-100-nm pores stabilize water through strong capillary forces, enabling operation at feed pressures above 72 bar under dry and humid conditions. Selectivity is governed by gas solubility in water, while permeance is tuned by adjusting the water layer thickness. Reducing this thickness below 200 nm yields CO2 permeances up to 11,600 gas permeation units with CO2:N2, CO2:CH4, and CO2:H2 selectivities of 40, 26, andmore » 31, respectively, surpassing the performance of state-of-the-art membranes. Operation is sustained for over a week without water loss, and performance scales using commercially available porous polymer supports under mixed-gas crossflow conditions. Water's dissolution-based transport avoids saturation and reaction-rate limits, enabling a robust, high-performance, and environmentally benign gas separation platform.« less

  8. Advancing the Performance of Anion Exchange Membrane Electrolysis by Employing a Powder-Based Ionomer during Anode Catalyst Layer Fabrication

    Chan, Ai-Lin ; Clauser, Arielle L. ; Parimuha, Makenzie R. ; ... - ACS Applied Energy Materials
    The performance of anion exchange membrane water electrolysis (AEMWE) can be significantly improved by utilizing powdered ionomers during the fabrication of the anode catalyst layer (CL) to modify the CL properties. When comparing powdered ionomers to dispersed ionomers across various catalysts including cobalt oxide (Co3O4), nickel−iron oxide (NiFe2O4), and iridium oxide (IrO2) the anode fabricated with powdered ionomers demonstrates improved performance in polarization curves, enhanced charge transfer kinetics, and reduced ohmic and transport losses, as evidenced by voltage breakdown and electrochemical impedance spectroscopy analyses. Optimal performance is achieved using a Co3O4 catalyst with a 10 wt % powdered ionomer viamore » the catalystcoated substrate method. Microscopy analyses reveal that electrodes formed with powdered ionomers during fabrication exhibit a more uniform catalyst and ionomer distribution, increased porosity with smaller pore areas, improved electronic conduction with less catalyst agglomeration isolated by a nonconductive ionomer, and enhanced interfacial contact with the membrane and transport layer. These findings highlight that ionomers in a powdered form can promote beneficial properties and are a promising approach to improving AEMWE efficiency.« less

  9. Proton Conducting Silicon Oxide Membranes as a Fluorine Free Alternative to Nafion for Low Temperature Water Electrolysis

    Jin, Jingjing ; Cohen, Lucas A. ; Adibnia, Sahand ; ... - ACS Applied Materials and Interfaces
    Driven by environmental and health concerns related to per- and polyfluoroalkyl substances (PFAS), there has been growing interest in developing fluorine-free proton (H+) exchange membrane (PEM) materials for fuel cells and water electrolyzers. In this study, we present a side-by-side comparison of the key transport properties of submicron thick, PFAS-free amorphous silicon dioxide (SiO2) membranes to Nafion, a fluorinated polymer electrolyte membrane that represents the industry standard for PEM fuel cells and electrolyzers. Here, measurements of proton (H+) conductivity (σH+), hydrogen (H2) permeability (PH2), and electrical resistivity (ρe–) were conducted using model thin films comprised of SiO2 membranes deposited bymore » atomic layer deposition (ALD). Although the H+ conductivity of the SiO2 membranes is 2–3 orders of magnitude lower than Nafion, the addition of phosphorus dopants (POx) improves H+ conductivity such that the area specific membrane resistance of thin (<50 nm) POx-doped SiO2 membranes is more than an order of magnitude lower than Nafion-117. Importantly, the safe operation of such nanoscale membranes within a PEM electrolyzer is feasible thanks to the low H2 permeability of dense SiO2-based membranes, which are predicted to limit H2 crossover rates to acceptable levels for pressures up to ≈ 100 bar. As a proof-of-principle demonstration, a chip-scale water electrolyzer based on 100 nm thick POx-SiO2 membrane is shown to achieve a current density of 2 A cm–2 at a potential of 2.5 V. If this technology can be successfully scaled up, H+ conducting oxide membranes offer an attractive PFAS-free alternative to Nafion for efficient and durable water electrolysis and fuel cell technologies.« less

  10. Stimulated Raman Scattering Microscopy: Real-Time In-Situ Physical and Chemical Characterization of Reverse Osmosis Desalination Membrane Scaling

    Simmons, Y. Lange ; Andersen, Jasmine M. ; Zohrabi, Mo ; ... - Environmental Science and Technology
    We introduce a stimulated Raman scattering (SRS) methodology designed for rapid, real-time, and in situ monitoring of RO membrane scaling adapted for bench-scale desalination flow cells. The methodology can provide new insights into membrane scaling dynamics by offering time-resolved reflection imaging of inorganic crystal growth, coupled with chemical identification from Raman spectral data. These capabilities allow for direct local measurement of the membrane surface area covered by different scalants as well as an approximation of the scalant volume using three-dimensional, integrated Raman intensity. The 2D and 3D SRS results obtained from CaSO4 scaling experiments are compared to and are inmore » reasonable agreement with those provided by confocal microscopy. The real-time physical and chemical characterization capabilities presented here could be extended to study combinations of inorganic, organic, and biological fouling. Overall, the SRS methodology represents an advancement in real-time sensing of membrane fouling that offers the potential for improved operation, lower cost, and more resilient RO membrane systems for sustainable water management.« less
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