Inorganic solid-state hydroxide ion conductors have emerged as stable platforms for high-temperature alkaline energy conversion technologies. Although several materials have shown promising ionic conductivity in model studies, their direct implementation in operating devices has remained largely unexplored. Here, we demonstrate that silver-(I) oxide (Ag2O) nanoparticles can function as hydroxide ion conductors within anion exchange membrane fuel cells (AEMFCs). Syringe-filtered 1-6 nm Ag2O nanoparticles were integrated into Pt/C cathodes, establishing ionic conduction pathways across the cathode-membrane interface. The resulting ionomer-free membrane electrode assembly (MEA) achieved 1.91 W cm-2 peak power density at 2.4 wt % Ag2O loading and maintained stable mass transport during 100 h of continuous operation at 0.6 A cm-2. Electrochemical and structural analyses revealed how Ag2O loading influences ionic conduction, pore structure, and mass transport behavior in ways that are partially distinct from conventional ionomer-based electrodes. These findings highlight inorganic solid-state conductors as promising design analogues to ionomers for high-performance, ionomer-free AEMFC cathodes.

Zn-air batteries (ZABs) are promising energy storage systems, but their performance is often limited by sluggish oxygen reduction reaction (ORR) kinetics and electrolyte flooding at the air cathode. Here, we introduce a tri-continuous carbon-based electrocatalyst (TRICE) derived from bijels-templated carbonization to address these challenges. The resulting nanoporous framework provides interconnected channels for air and electrolyte, enhancing three-phase boundary formation and mass transport. To investigate the role of wettability, two TRICE samples, specifically unmodified and hydrophobic TRICE were evaluated. The hydrophobic TRICE electrodes exhibited strong resistance to electrolyte flooding and maintained stable electrochemical operation during repeated cycling. Despite being fully metal-free, their power densities remained competitive with those of noble-metal and metal-oxide air cathodes. These results demonstrate that wettability tuning in TRICE structures effectively improves flooding tolerance and air cathode stability, offering a promising pathway for durable ZABs.

Abstract Visible-light-driven H2 evolution using dye-sensitized photocatalysts has attracted considerable attention as a molecularly tunable approach for solar fuel generation. Among various semiconductor platforms, metal oxide nanosheets derived from their host layered materials provide unique opportunities because of their atomically thin crystalline structures, anisotropic carrier transport properties, large surface areas, and highly tailorable interfacial chemistry. In this Account, we summarize our research on dye-sensitized H2-evolving photocatalysts based mainly on niobate nanosheets, with particular emphasis on the interplay between nanosheet structure, interfacial electron transfer, and photocatalytic function. Early studies demonstrated that exfoliated oxide nanosheets and nanoscrolls efficiently mediate visible-light-induced electron injection from Ru(II) sensitizers, enabling H2 evolution even without covalent dye anchoring. Subsequent work revealed how nanosheet composition/crystallinity, cocatalyst deposition and dye structure govern charge separation and back electron transfer. More recent studies have established artificial Z-scheme systems for solar-driven overall water splitting and clarified excited-carrier dynamics through spectroscopic investigations. These findings highlight oxide nanosheets as versatile platforms for constructing highly organized hybrid photocatalysts and provide design principles for future solar-to-hydrogen conversion systems utilizing molecular–solid interfaces.

Methanol, an important liquid fuel and chemical feedstock, has yet to be produced using solar energy, H2O, and CO2 as sole inputs in a standalone device. This study directly addresses this longstanding challenge through presenting the first demonstration of unbiased solar methanol production from CO2 and H2O with a monolithic artificial leaf design, surpassing the previous best energy efficiency in solar alcohol production by at least 1 order of magnitude. We first develop a new generation of photocathodes based on Si micropillar arrays and a cobalt tetraaminophthalocyanine molecular catalyst. By integrating a C60 interlayer that facilitates unidirectional electron transfer through the semiconductor/catalyst interface, we realize a photovoltage of 500 mV, one of the highest recorded for single-junction Si-based photoelectrodes in aqueous CO2 reduction, as well as unprecedented methanol formation with a Faradaic efficiency of 30% and a partial current density of 6.3 mA cm-2. We further integrate the photocathode with a multijunction perovskite photovoltaic minimodule to afford a standalone solar fuel system, which demonstrates a light-to-methanol conversion efficiency of 0.8%, 32 times higher than the present record in light-to-alcohol conversion with an artificial leaf.

Neutral or basic conditions are commonly required for the selective electrochemical reduction of CO2, leading to the accumulation of carbonate salts and the generation of formate rather than formic acid. A generalizable strategy for obtaining formic acid (not formate) in the electroreduction of CO2 with molecular catalysts is introduced, based on controlling acidity gradients using a dual-electrolyte cell with a proton-exchange membrane. This approach uses anodic water oxidation as the source of protons and electrons for CO2 reduction to formic acid, while mitigating H2 evolution near the cathode and avoiding carbonate formation. Mechanistic studies, including systems modeling, provide insight into the origin of the formic acid selectivity and guide the broader implementation of this strategy in molecular electrocatalysis for CO2 utilization.

The production of electrolytic hydrogen or Green Hydrogen has attracted the attention of scientists as a potential enabler of sustainable energy production. The cleavage of the water molecule requires high energy, in order to produce hydrogen and oxygen through their corresponding half reactions, the hydrogen evolution and oxygen evolution reactions. This latter reaction has been studied in more detail, since its slow kinetics make the water electrolysis less efficient, and, for instance, delay the formation of hydrogen in the counter compartment of the electrolytic cell. In this work, a study of the oxygen evolution reaction is presented. For this, a series of rhenium catalysts deposited onto stainless steel 316 are studied with the aim of analyzing the effect of the pure metal (Re) and the metal with heteroatoms (Re-C, Re-B, and Re-O). As one of the problems worldwide is the scarcity of freshwater, the study focuses on the performance of this series of catalysts in highly saline environments, representative of seawater. The synthesis and electrochemical performance is shown, giving high expectations that these electrocatalysts could be potential electrocatalysts in marine environments.

Electrochemical CO2 reduction using renewable sources of electrical energy holds promise for converting CO2 into fuels and chemicals. The complex interactions among chemical/electrochemical reactions and mass transport make it difficult to analyze the effect of an individual process on electrode performance based only on experimental methods. Here, we developed a generalized steady-state simulation to describe an electrode surface in which sequential cascade catalysts are patterned in a periodic trench design. If appropriately constructed, this trench geometry is hypothesized to be able to yield a higher net current density for a CO2 reduction (CO2R) cascade reaction. We have used realistic experimental reaction kinetics to investigate the role of trench geometry in mass transport, local microenvironments, and selectivity for a model CO2R cascade reaction. The model considers local concentration gradients of bicarbonate species at quasi-equilibrium and catalytic surface reactions based on concentration-dependent Butler-Volmer kinetics. Our results suggest that varying the spatial distribution of active sites plays a significant role in facilitating effective mass transport between active sites, modulating selectivity for the cascade reaction, and enhancing the yield of desirable cascade products. Moreover, we observe that this trench geometry significantly alters the cascade reaction rate by affecting the local pH, which can cause inadvertent depletion of available aqueous CO2 to limit the CO2R cascade kinetics and modest suppression of the hydrogen evolution reaction (HER). The results highlight the trade-offs between mass transport, pH, and reaction kinetics that become apparent only when considering the coupled physics of all processes at the electrode surface. This model can thus serve as a primary tool to build more selective and efficient patterned architectures for the CO2R cascade catalysis.

While redox polymer-mediated catalysis at silicon photoelectrodes has been studied since the 1980s, there have been few detailed studies of these materials in photoelectrochemical CO2 reduction. Here, we develop silicon photoelectrodes functionalized with a viologen-based polymer that mediates the formation of catalytic gold nanoparticles. The presence of gold was confirmed by X-ray photoelectron spectroscopy (XPS), and the nanoparticles were imaged with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). We probed the CO2 reduction process during bulk photoelectrolysis to find modest, yet consistent CO faradaic efficiencies across a range of applied potentials. Operando surface-enhanced Raman spectroscopy (SERS) was used to measure the Fermi levels of both the viologen polymer and the Au catalyst sites. The operando measurement of the Fermi levels of all three components of the photocathode provides a unified picture of the electron transfer process in the semiconductor-redox polymer-catalyst system. The redox polymer serves as the electron transfer mediator between the Si substrate and Au sites. In addition, the Au Fermi level equilibrates with the Fermi level of the viologen polymer, which in turn fixes the quasi-Fermi level of Au catalysts at the p-Si/redox polymer interface. This suggests a potential future direction of using redox polymers with tunable potentials to modulate the potential of metal cocatalysts and thus control the reaction selectivity.

An Os-(II) polypyridyl complex was applied as a photosensitizer in dye-sensitized photocatalyst systems based on Pt-intercalated HCa2Nb3O10 and Pt-loaded TiO2. The Os-(II) complex exhibits a spin-forbidden but partially allowed triplet metal-to-ligand charge transfer (3MLCT) transition, enabling broad visible light absorption up to 800 nm, which surpasses that of conventional Ru-(II)-based dyes. Despite its shorter excited-state lifetime compared to Ru-(II) complexes, efficient electron injection from the excited Os-(II) dye into the semiconductor was confirmed. Under visible-light irradiation, the Os-(II)-sensitized photocatalysts showed higher H2 evolution activity than the Ru-(II)-sensitized photocatalysts when sodium ascorbate was used as an electron donor, demonstrating effective utilization of long-wavelength visible light. In contrast, negligible H2 evolution was observed when NaI was employed as a redox mediator for Z-scheme water splitting. Transient absorption spectroscopy revealed that the lack of activity stemmed from inefficient electron transfer from I- to oxidized Os-(II). These findings highlight the importance of selecting appropriate redox mediators to fully exploit long-wavelength dyes for overall water splitting under visible light.

Bipolar membranes (BPMs) are interesting materials for the development of next-generation electrochemical energy conversion and separations processes. One of the key challenges in optimizing BPM performance is enhancing the rate of the water dissociation (WD) reaction. While electric field effects, specifically the second Wien effect, have been demonstrated to enhance the rate of WD reaction, making BPMs with low overpotentials for WD using primary electric field effects has been difficult to achieve. In this study, we constructed an abrupt interfacial structure between the anion exchange membrane (AEM) and cation exchange membrane (CEM) of BPMs to maximize the intensity of local electric field. A film of densely tiled, molecularly thin titanium oxide nanosheets was deposited as the interfacial layer to create an abrupt interface for studying extreme electric field effects. Although BPMs with titanium oxide nanosheet films exhibited higher WD reaction resistance compared to thicker catalyst layers composed of nanoparticles at low current density, they showed superior performance at higher current densities, where strong electric fields were present, and an apparent WD overpotential of 0.25 V at 300 mA cm-2 was extracted from electrochemical impedance measurements. These results highlight the potential of optimizing BPM performance by maximizing the second Wien effect through the utilization of two-dimensionally assembled nanosheet films.

The ability to efficiently create ordered colloidal monolayers on solid surfaces is critical for nanosphere lithography and related applications. We describe here a simple automated method for growing well-ordered 2D crystals of polystyrene spheres at an air-water interface and transferring them to silicon substrates on the wafer scale. The method exploits the Marangoni effect and is enhanced by surface treatment of both the basin for monolayer formation and the intended substrate for transfer. Quantitative image analysis of the sphere monolayers shows that the monolayer packing is improved by automation. Dual-droplet automation is shown to be useful for controlling 2D crystal growth and forming phase-separated monolayers from two different colloidal particle sizes.

The precise control of thickness at the subnanometer scale is essential for tuning the properties of two-dimensional (2D) nanosheets. However, the thickness control of free-standing nanosheets composed of nonlayered compounds remains a fundamental challenge. Here, we report a solid-state surfactant templating strategy for synthesizing free-standing amorphous siloxane nanosheets with subnanometer thickness precision. By tailoring the length of ethylene oxide chains of the surfactant, we reproducibly obtained nanosheets with precisely defined thicknesses of 0.9, 1.5, 2.0, and 2.5 nm, while also enabling the incorporation of organofunctional groups into their frameworks. The resulting nanosheets exhibit thickness uniformity and high colloidal stability, enabling the formation of densely packed large-area films suitable for the systematic investigation of the properties, such as band gaps and breakdown strengths. We found that amorphous silica nanosheets showed exceptionally low overpotentials for the water dissociation reaction with a clear thickness dependence despite amorphous silica being widely regarded as a poor catalyst.

InfoMetricsFiguresRef. Chemistry of MaterialsASAPArticle This publication is free to access through this site. Learn More CiteCitationCitation and abstractCitation and referencesMore citation options ShareShare onFacebookX (Twitter)WeChatLinkedInRedditEmailJump toExpandCollapse ORIGINAL ARTICLE. This notice is a correction.Addition/CorrectionJanuary 10, 2025Correction to "Solid-State Hydroxide Ion Conductivity in Silver(I) Oxide, Ag2O"Click to copy article linkArticle link copied!Leanna SchulteLeanna SchulteMore by Leanna Schultehttps://orcid.org/0000-0002-6970-8811Shihan QinShihan QinMore by Shihan Qinhttps://orcid.org/0009-0008-1587-978XWonil JungWonil JungMore by Wonil JungChristy GeorgeChristy GeorgeMore by Christy Georgehttps://orcid.org/0000-0001-9210-2394Jarrett D. DillenburgerJarrett D. DillenburgerMore by Jarrett D. Dillenburgerhttps://orcid.org/0000-0001-8274-6452Akshay VenkateshAkshay VenkateshMore by Akshay VenkateshMuhammad K. IshakMuhammad K. IshakMore by Muhammad K. IshakNichole M. WonderlingNichole M. WonderlingMore by Nichole M. WonderlingSariah MarthSariah MarthMore by Sariah MarthHeemin ParkHeemin ParkMore by Heemin ParkChulsung BaeChulsung BaeMore by Chulsung Baehttps://orcid.org/0000-0002-9026-3319Andrew M. Rappe*Andrew M. RappeMore by Andrew M. Rappehttps://orcid.org/0000-0003-4620-6496Thomas E. Mallouk*Thomas E. MalloukMore by Thomas E. Malloukhttps://orcid.org/0000-0003-4599-4208Open PDFChemistry of MaterialsCite this: Chem. Mater. 2025, XXXX, XXX, XXX-XXXClick to copy citationCitation copied!https://pubs.acs.org/doi/10.1021/acs.chemmater.4c03525https://doi.org/10.1021/acs.chemmater.4c03525Published January 10, 2025 Publication History Received 26 December 2024Published online 10 January 2025correction© 2025 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissionsThis publication is licensed for personal use by The American Chemical Society. ACS Publications© 2025 American Chemical SocietyIn the description of doping by reactions (2) and (3) on p. 11455, both reactions were described as "oxidative." Only reaction (3) represents oxidative doping. The product of reaction (2) was written as Ag2–x(HxO)(OH)x, but the correct formula is Ag2–xHxO. The formula weight, written as (231.74 – 91.86x) g/mol, is corrected to (231.74 – 106.8x) g/mol, and accordingly the lowering of the density at the x = 0.01 doping level by reaction (2) is corrected from 0.40% to 0.46%; the raising of the density by reaction (3) is corrected from 0.05% to 0.07%.In the description of the hydroxide conductivity mechanism on p. 11455, it was stated that both the single and tandem OH– systems are diamagnetic. Figures S10–S13 show that the single OH– system is paramagnetic, whereas the tandem OH– system is diamagnetic.On p. 11456, it was stated that NMR chemical shifts were calculated from the structures shown in Figure S15. The correct figure number is S16.Author InformationClick to copy section linkSection link copied!Corresponding AuthorsAndrew M. Rappe; https://orcid.org/0000-0003-4620-6496Thomas E. Mallouk; https://orcid.org/0000-0003-4599-4208AuthorsLeanna Schulte; https://orcid.org/0000-0002-6970-8811Shihan Qin; https://orcid.org/0009-0008-1587-978XWonil JungChristy George; https://orcid.org/0000-0001-9210-2394Jarrett D. Dillenburger; https://orcid.org/0000-0001-8274-6452Akshay VenkateshMuhammad K. IshakNichole M. WonderlingSariah MarthHeemin ParkChulsung Bae; https://orcid.org/0000-0002-9026-3319Cited By Click to copy section linkSection link copied!This article has not yet been cited by other publications.Download PDFFiguresReferences Get e-AlertsGet e-AlertsChemistry of MaterialsCite this: Chem. Mater. 2025, XXXX, XXX, XXX-XXXClick to copy citationCitation copied!https://doi.org/10.1021/acs.chemmater.4c03525Published January 10, 2025 Publication History Received 26 December 2024Published online 10 January 2025© 2025 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissionsArticle Views-Altmetric-Citations-Learn about these metrics closeArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated.Recommended Articles FiguresReferencesThis publication has no figures.This publication has no References.

We report two Cu(i)-tren host molecules with unusual air-stability, as revealed by strong preference for axial CO binding over bent O2. Spectroscopy, electrochemical, and X-ray crystal structure analyses indicate that the phenyl rotators of the capsule select for small axial ligands.

A soft lithographic method is developed for making bipolar membranes (BPMs) with catalytic junctions formed from arrays of vertically oriented microscale cylinders. The membranes are cast from reusable polydimethylsiloxane (PDMS) molds made from silicon masters, which are fabricated on 2 '' to 4 '' wafer scales by nanosphere lithography. High-aspect-ratio junctions are made on a length scale similar to the thickness of optimized catalyst layers for water dissociation, creating a platform for probing the dual effects of catalysis and local electric field at the microscale BPM junction. Optimized polymer materials and nanoscale metal oxide catalysts are used in this study. 3D BPMs are tested under reverse and forward bias conditions, exhibiting superior performance relative to their 2D counterparts. Under forward bias in H2-O2 fuel cells, 3D BPMs achieve a current density of 1500 mA cm-2, approximate to 7 times higher than 2D membranes made from the same materials.

Graphite oxide (GO) has been widely studied as an interfacial layer in bipolar membranes because of its activity as a catalyst for the water dissociation and acid-base neutralization reactions. However, the roles of GO nanosheet size, orientation, and surface coverage in controlling its catalytic activity are not well understood. GO nanosheets with lateral dimensions of several microns were prepared by oxidative exfoliation of natural graphite crystals, enabling their orientation and coverage to be observed directly by optical microscopy. The coverage and orientation of the GO nanosheets were measured as a function of different deposition methods, which included solution adsorption, Langmuir-Blodgett transfer from an air-water interface, and spray-coating. Highly oriented GO films made by the Langmuir-Blodgett method gave the best performance metrics. Interestingly, full coverage of the bipolar interface by GO nanosheets resulted in lower performance than partial coverage. This effect could be rationalized in terms of the differential permeability of H+ and OH- ions through GO, which leads to concentration polarization of OH- on one side of the sheets.

Efficient and stable photoelectrochemical reduction of CO2 into highly reduced liquid fuels remains a formidable challenge, which requires an innovative semiconductor/catalyst interface to tackle. In this study, we introduce a strategy involving the fabrication of a silicon micropillar array structure coated with a superhydrophobic fluorinated carbon layer for the photoelectrochemical conversion of CO2 into methanol. The pillars increase the electrode surface area, improve catalyst loading and adhesion without compromising light absorption, and help confine gaseous intermediates near the catalyst surface. The superhydrophobic coating passivates parasitic side reactions and further enhances local accumulation of reaction intermediates. Upon one-electron reduction of the molecular catalyst, the semiconductor-catalyst interface changes from adaptive to buried junctions, providing a sufficient thermodynamic driving force for CO2 reduction. These structures together create a unique microenvironment for effective reduction of CO2 to methanol, leading to a remarkable Faradaic efficiency reaching 20% together with a partial current density of 3.4 mA cm(-2), surpassing the previous record based on planar silicon photoelectrodes by a notable factor of 17. This work demonstrates a new pathway for enhancing photoelectrocatalytic CO2 reduction through meticulous interface and microenvironment tailoring and sets a benchmark for both Faradaic efficiency and current density in solar liquid fuel production.

Frustules, or the silica based cell walls of diatomaceous algae Aulacoseira granulata, provide large numbers of reliably cylindrical microstructures with an inner cavity and surface chemistry suitable for constructing bubble-based, acoustically-powered micro-swimmers. In this way, microswimmers can be made in a scalable, accessible and low-cost manner, enabling studies of their individual and collective behavior as active colloids.

Silver(I) oxide, Ag2O, precipitated as microcrystals by combining aqueous silver(I) nitrate and KOH solutions, was found to be a solid-state hydroxide ion conductor with ionic conductivity on the order of 10-3 S/cm. The proton chemical shifts at 4.87 and -7.35 ppm measured by solid-state 1H NMR experiments are attributed to water molecules and in-lattice OH- coordinated to silver, respectively. The lack of spinning sidebands around the 4.87 ppm peak indicates rapid reorientation on the NMR time scale, suggesting that the water molecules are adsorbed to the surface of the Ag2O crystals. Pulsed field gradient measurements gave similar diffusion coefficients (2 x 10-7 cm2/s at 298 K) for all three proton environments, indicating chemical exchange between sites on the millisecond time scale. The activation energy for OH- diffusion measured by NMR (0.18 eV) was comparable to that obtained by conductivity measurements and density functional theory (DFT) electronic structure calculations. The calculated Pourbaix diagram of Ag2O is consistent with the slightly lower sample density observed in He pycnometry and thermogravimetric measurements.