Materials Science and Engineering

Proton transfer at electrochemical interfaces is fundamentally important across science and technology, yet kinetic measurements of this elementary step at electrode|electrolyte interfaces are convoluted with other electron-transfer steps and by inhomogeneous electrode surfaces. We use facilitated proton transfer at the interface between two immiscible electrolyte solutions (ITIES) as a platform to study proton-transfer kinetics in the absence of interfacial electron transfer and without the defects at solid|electrolyte interfaces. Diffusion-controlled micropipette voltammetry revealed that 2,6-diphenylpyridine (DPP) facilitates proton transfer across the HCl(aq)|trifluorotoluene interface, while voltammetry at nanopipette-supported interfaces yielded activation-controlled ion-transfer currents. We extract kinetic parameters k_app⁰ and α_app, 3.0 ± 1.8 cm/s and 0.3 ± 0.2, respectively, for DPP-facilitated proton transfer by fitting quasi-reversible voltammograms to a mixed diffusive-kinetic model. Finite-element simulations highlighted regimes of direct proton transfer and sequential proton transfer, where the current divided between these two possible pathways was shown to favor direct proton transfer when the neutral partitioning step DPP(org) → DPP(aq) was rate-determining. Atomistic molecular-dynamics simulations were used to compute the free energy change to move DPP and its protonated analogue within, and across, the liquid|liquid interface. The most-likely location for proton transfer is predicted to be in the surface region where significant interpenetration of the two liquids occurs. Understanding the kinetics of ion transfer at the ITIES illustrated here is important in the development of general theories of ion transfer in electrochemical science and technology.

Understanding processes in photon-phonon scattering, absorption, and chemical reactions in optical nanocavities is important for single-molecule sensors, single-photon emitters, and photocatalysis. However, the influence of electromagnetic fields, charge transfer, and molecular geometry is challenging to probe by ensemble-averaged spectroscopic techniques over multiple nanocavities. Photoinduced force microscopy (PiFM), which measures photoinduced polarizability under infrared excitation of a sample in the nanocavity between the scanning probe microscopy tip and sample surface, is used here for simultaneous nanoscale topological and chemical characterization. First-principles density functional theory (DFT) simulations of the vibrational spectra of gold nanoparticle surfaces functionalized with benzenedithiol (Au-BDT) elucidate molecular orientation, charge transfer, and oxidation state for understanding molecular and adatom reconfiguration in optical nanocavities in response to external fields.

In today's rapidly evolving quantum landscape, the generation and manipulation of quantum light not only represent fundamental challenges but also herald unprecedented opportunities in communication, computing, sensing, and imaging. This special issue brings together a collection of contributions that span the entire journey, from the creation of quantum light using novel materials and emitters to its seamless integration into photonic architectures and eventual deployment in advanced quantum applications. This special issue, "Quantum Light: Creation, Integration, and Applications," features a collection of three review articles, five perspectives, and 23 original research papers, highlighting both the timeliness of the topic and the remarkable breadth and richness of ongoing advancements in the field.

As an emerging technology, polymer electrolyte fuel cells (PEFCs) powered by clean hydrogen can be a great source of renewable power generation with flexible utilization because of high gravimetric energy density of hydrogen. To be used in real-life applications, PEFCs need to maintain their performance for long-term use under a wide range of conditions. Therefore, it's important to understand the degradation of the PEFC under protocols that are closely related to the catalyst lifetime. Alloying Pt with transitional metal improves catalyst activity. It is also crucial to understand Pt alloys degradation mechanisms to improve their durability. To study durability of Pt alloys, accelerated stress tests (ASTs) are performed on Pt−Co catalyst supported on two types of carbon. Two different AST protocols were being studied: Membrane Electrolyte Assembly (MEA) AST based on the protocol introduced by the Million Mile Fuel Cell Truck consortium in 2023 and Catalyst AST, adopted from the U.S. Department of Energy (DoE).

As space exploration continues to evolve, researchers have been investigating ways to develop low-cost landing systems. Lattice structures are an attractive option for reducing costs during terrestrial landings due to their lightweight character and energy absorption capacity. The ability to produce complex geometries, specifically lightweight lattice structures, makes additive manufacturing an attractive method for producing energy absorbing lattices. During this project, various stereolithography 3D printed lattice structures were designed, manufactured, and tested for their energy absorption capacities. The findings from this study could significantly advance low-cost, high-performance landing solutions for future terrestrial missions, enabling more efficient space exploration.

Biology provides many sources of inspiration for synthetic and multifunctional nanomaterials. Naturally evolved proteins exhibit specialized, sequence-defined functions and self-assembly behavior. Recapitulating their molecularly defined self-assembly behavior, however, is challenging in de novo proteins. Peptides, on the other hand, represent a more well-defined and rationally designable space with the potential for sequence-programmable, stimuli-responsive design for structure and function, making them ideal building blocks of bioelectronic interfaces. In this work, we design peptides that exhibit stimuli-responsive self-assembly and the capacity to transport electrical current over micrometer-long distances. A lysine-lysine (KK) motif inserted at solvent-exposed positions of a coiled-coil-forming peptide sequence introduces pH-dependent control over a transition from unordered to α-helical peptide structure. The ordered state of the peptide serves as a building block for the assembly of coiled coils and higher-order assemblies. Cryo-EM structures of these structures reveal a hierarchical organization of α-helical peptides in a cross coiled coil (CCC) arrangement. Structural analysis also reveals a β-sheet fiber phase under certain conditions and placements of the KK motif, revealing a complex and sensitive self-assembly pathway. Both solid-state and solution-based electrochemical characterizations show that CCC fibers are electronically conductive. Single-fiber conductive AFM measurement indicates that the solid-state electrical conductivity is comparable with bacterial cytochrome filaments. Solution-deposited fiber films approximately doubled the electroactive surface area of the electrode, confirming their conductivity in aqueous environments. This work establishes a stimuli-responsive peptide sequence element for balancing the order-disorder transitions in peptides to control their self-assembly into highly organized electronically conductive nanofibers.

Understanding bacterial physiology in real-world environments requires noninvasive approaches and is a challenging yet necessary endeavor to effectively treat infectious disease. Bacteria evolve strategies to tolerate chemical gradients associated with infections. The DIVER (Deep Imaging Via Enhanced Recovery) microscope can image autofluorescence and fluorescence lifetime throughout samples with high optical scattering, enabling the study of naturally formed chemical gradients throughout intact biofilms. Using the DIVER, a long fluorescent lifetime signal associated with reduced pyocyanin, a molecule for electron cycling in low oxygen, was detected in low-oxygen conditions at the surface of Pseudomonas aeruginosa biofilms and in the presence of fermentation metabolites from Rothia mucilaginosa, which cocolonizes infected airways with P. aeruginosa. These findings underscore the utility of the DIVER microscope and fluorescent lifetime for noninvasive studies of bacterial physiology within complex environments, which could inform on more effective strategies for managing chronic infection.

Understanding bacterial physiology in real-world environments requires noninvasive approaches and is a challenging yet necessary endeavor to effectively treat infectious disease. Bacteria evolve strategies to tolerate chemical gradients associated with infections. The DIVER (Deep Imaging Via Enhanced Recovery) microscope can image autofluorescence and fluorescence lifetime throughout samples with high optical scattering, enabling the study of naturally formed chemical gradients throughout intact biofilms. Using the DIVER, a long fluorescent lifetime signal associated with reduced pyocyanin, a molecule for electron cycling in low oxygen, was detected in low-oxygen conditions at the surface of Pseudomonas aeruginosa biofilms and in the presence of fermentation metabolites from Rothia mucilaginosa, which cocolonizes infected airways with P. aeruginosa. These findings underscore the utility of the DIVER microscope and fluorescent lifetime for noninvasive studies of bacterial physiology within complex environments, which could inform on more effective strategies for managing chronic infection.

The discovery of Nb-W-O materials years ago marks the milestone of charging a lithium-ion battery in minutes. Nevertheless, for many applications, charging lithium-ion battery within one minute is urgently demanded, the bottleneck of which largely lies in the lack of fundamental understanding of Li+ storage mechanisms in these materials. Herein, by visualizing Li+ intercalated into representative Nb16W5O55, we find that the fast-charging nature of such material originates from an interesting rate-dependent lattice relaxation process associated with the Jahn-Teller effect. Furthermore, in situ electron microscopy further reveals a directional, [010]-preferred Li+ transport mechanism in Nb16W5O55 crystals being the bottleneck toward fast charging that deprives the entry of any desolvated Li+ through the prevailing non-(010) surfaces. Hence, we propose a machine learning-assisted interface engineering strategy to swiftly collect desolvated Li+ and relocate them to (010) surfaces for their fast intercalation. As a result, a capacity of ≈ 116 mAh g-1 (68.5% of the theoretical capacity) at 80 C (45 s) is achieved when coupled with a Li negative electrode.

Abstract: The aim of this study is to enable the hydrogen economy and decarbonize various sectors in our environment that requires less expensive and more durable water electrolyzers, which can meet the Hydrogen-Shot target. The key is to improve the ionomer interfaces in low-temperature water electrolyzers as rapidly as possible, but to do so, it requires a systematic and holistic campaign combining both experiments and theory. In this perspective, we discuss the issues of electrolyzers and needs for translational science. We then present the approach that the Energy EarthShot Research Center: Center for Ionomer-based Water Electrolysis is taking in hopes of inspiring the community with this approach that can be leveraged to multiple problems and technologies.