Single-site iron-anchored amyloid hydrogels as catalytic platforms for alcohol detoxification.

Constructing effective antidotes to reduce global health impacts induced by alcohol prevalence is a challenging topic. Despite the positive effects observed with intravenous applications of natural enzyme complexes, their insufficient activities and complicated usage often result in the accumulation of toxic acetaldehyde, which raises important clinical concerns, highlighting the pressing need for stable oral strategies. Here we present an effective solution for alcohol detoxification by employing a biomimetic-nanozyme amyloid hydrogel as an orally administered catalytic platform. We exploit amyloid fibrils derived from ß-lactoglobulin, a readily accessible milk protein that is rich in coordinable nitrogen atoms, as a nanocarrier to stabilize atomically dispersed iron (ferrous-dominated). By emulating the coordination structure of the horseradish peroxidase enzyme, the single-site iron nanozyme demonstrates the capability to selectively catalyse alcohol oxidation into acetic acid, as opposed to the more toxic acetaldehyde. Administering the gelatinous nanozyme to mice suffering from alcohol intoxication significantly reduced their blood-alcohol levels (decreased by 55.8% 300 min post-alcohol intake) without causing additional acetaldehyde build-up. Our hydrogel further demonstrates a protective effect on the liver, while simultaneously mitigating intestinal damage and dysbiosis associated with chronic alcohol consumption, introducing a promising strategy in effective alcohol detoxification.

Complementary probes for the electrochemical interface.

The functions of electrochemical energy conversion and storage devices rely on the dynamic junction between a solid and a fluid: the electrochemical interface (EI). Many experimental techniques have been developed to probe the EI, but they provide only a partial picture. Building a full mechanistic understanding requires combining multiple probes, either successively or simultaneously. However, such combinations lead to important technical and theoretical challenges. In this Review, we focus on complementary optoelectronic probes and modelling to address the EI across different timescales and spatial scales - including mapping surface reconstruction, reactants and reaction modulators during operation. We discuss how combining these probes can facilitate a predictive design of the EI when closely integrated with theory.

Molecular surface programming of rectifying junctions between InAs colloidal quantum dot solids.

Heavy-metal-free III-V colloidal quantum dots (CQDs) show promise in optoelectronics: Recent advancements in the synthesis of large-diameter indium arsenide (InAs) CQDs provide access to short-wave infrared (IR) wavelengths for three-dimensional ranging and imaging. In early studies, however, we were unable to achieve a rectifying photodiode using CQDs and molybdenum oxide/polymer hole transport layers, as the shallow valence bandedge (5.0 eV) was misaligned with the ionization potentials of the widely used transport layers. This occurred when increasing CQD diameter to decrease the bandgap below 1.1 eV. Here, we develop a rectifying junction among InAs CQD layers, where we use molecular surface modifiers to tune the energy levels of InAs CQDs electrostatically. Previously developed bifunctional dithiol ligands, established for II-VI and IV-VI CQDs, exhibit slow reaction kinetics with III-V surfaces, causing the exchange to fail. We study carboxylate and thiolate binding groups, united with electron-donating free end groups, that shift upward the valence bandedge of InAs CQDs, producing valence band energies as shallow as 4.8 eV. Photophysical studies combined with density functional theory show that carboxylate-based passivants participate in strong bidentate bridging with both In and As on the CQD surface. The tuned CQD layer incorporated into a photodiode structure achieves improved performance with EQE (external quantum efficiency) of 35% (>1 µm) and dark current density < 400 nA cm-2, a >25% increase in EQE and >90% reduced dark current density compared to the reference device. This work represents an advance over previous III-V CQD short-wavelength IR photodetectors (EQE < 5%, dark current > 10,000 nA cm-2).

Quantum-Tuned Cascade Multijunction Infrared Photodetector.

Emerging applications such as augmented reality, self-driving vehicles, and quantum information technology require optoelectronic devices capable of sensing a low number of photons with high sensitivity (including gain) and high speed and that could operate in the infrared at telecom windows beyond silicon's bandgap. State-of-the-art semiconductors achieve some of these functions through costly and not easily scalable doping and epitaxial growing methods. Colloidal quantum dots (QDs), on the other hand, could be easily tuned and are compatible with consumer electronics manufacturing. However, the development of a QD infrared photodetector with high gain and high response speed remains a challenge. Herein, we present a QD monolithic multijunction cascade photodetector that advances in the speed-sensitivity-gain space through precise control over doping and bandgap. We achieved this by implementing a QD stack in which each layer is tailored via bandgap tuning and electrostatic surface manipulation. The resulting junctions sustain enhanced local electric fields, which, upon illumination, facilitate charge tunneling, recirculation, and gain, but retain low dark currents in the absence of light. Using this platform, we demonstrate an infrared photodetector sensitive up to 1500 nm, with a specific detectivity of ∼3.7 × 1012 Jones, a 3 dB bandwidth of 300 kHz (0.05 cm2 device), and a gain of ∼70× at 1300 nm, leading to an overall gain-bandwidth product over 20 MHz, in comparison with 3 kHz of standard photodiode devices of similar areas.

Homomeric chains of intermolecular bonds scaffold octahedral germanium perovskites.

Perovskites with low ionic radii metal centres (for example, Ge perovskites) experience both geometrical constraints and a gain in electronic energy through distortion; for these reasons, synthetic attempts do not lead to octahedral [GeI6] perovskites, but rather, these crystallize into polar non-perovskite structures1-6. Here, inspired by the principles of supramolecular synthons7,8, we report the assembly of an organic scaffold within perovskite structures with the goal of influencing the geometric arrangement and electronic configuration of the crystal, resulting in the suppression of the lone pair expression of Ge and templating the symmetric octahedra. We find that, to produce extended homomeric non-covalent bonding, the organic motif needs to possess self-complementary properties implemented using distinct donor and acceptor sites. Compared with the non-perovskite structure, the resulting [GeI6]4- octahedra exhibit a direct bandgap with significant redshift (more than 0.5 eV, measured experimentally), 10 times lower octahedral distortion (inferred from measured single-crystal X-ray diffraction data) and 10 times higher electron and hole mobility (estimated by density functional theory). We show that the principle of this design is not limited to two-dimensional Ge perovskites; we implement it in the case of copper perovskite (also a low-radius metal centre), and we extend it to quasi-two-dimensional systems. We report photodiodes with Ge perovskites that outperform their non-octahedral and lead analogues. The construction of secondary sublattices that interlock with an inorganic framework within a crystal offers a new synthetic tool for templating hybrid lattices with controlled distortion and orbital arrangement, overcoming limitations in conventional perovskites.

High-rate and selective conversion of CO2 from aqueous solutions to hydrocarbons.

Electrochemical carbon dioxide (CO2) conversion to hydrocarbon fuels, such as methane (CH4), offers a promising solution for the long-term and large-scale storage of renewable electricity. To enable this technology, CO2-to-CH4 conversion must achieve high selectivity and energy efficiency at high currents. Here, we report an electrochemical conversion system that features proton-bicarbonate-CO2 mass transport management coupled with an in-situ copper (Cu) activation strategy to achieve high CH4 selectivity at high currents. We find that open matrix Cu electrodes sustain sufficient local CO2 concentration by combining both dissolved CO2 and in-situ generated CO2 from the bicarbonate. In-situ Cu activation through alternating current operation renders and maintains the catalyst highly selective towards CH4. The combination of these strategies leads to CH4 Faradaic efficiencies of over 70% in a wide current density range (100 - 750 mA cm-2) that is stable for at least 12 h at a current density of 500 mA cm-2. The system also delivers a CH4 concentration of 23.5% in the gas product stream.

Sequential Co-Passivation in InAs Colloidal Quantum Dot Solids Enables Efficient Near-Infrared Photodetectors.

III-V colloidal quantum dots (CQDs) are promising materials for optoelectronic applications, for they avoid heavy metals while achieving absorption spanning the visible to the infrared (IR). However, the covalent nature of III-V CQDs requires the development of new passivation strategies to fabricate conductive CQD solids for optoelectronics: this work shows herein that ligand exchanges, previously developed in II-VI and IV-VI quantum dots and employing a single ligand, do not fully passivate CQDs, and that this curtails device efficiency. Guided by density functional theory (DFT) simulations, this work develops a co-passivation strategy to fabricate indium arsenide CQD photodetectors, an approach that employs the combination of X-type methyl ammonium acetate (MaAc) and Z-type ligands InBr3 . This approach maintains charge carrier mobility and improves passivation, seen in a 25% decrease in Stokes shift, a fourfold reduction in the rate of first-exciton absorption linewidth broadening over time-under-stress, and leads to a doubling in photoluminescence (PL) lifetime. The resulting devices show 37% external quantum efficiency (EQE) at 950 nm, the highest value reported for InAs CQD photodetectors.

Introducing Brønsted acid sites to accelerate the bridging-oxygen-assisted deprotonation in acidic water oxidation.

Oxygen evolution reaction (OER) consists of four sequential proton-coupled electron transfer steps, which suffer from sluggish kinetics even on state-of-the-art ruthenium dioxide (RuO2) catalysts. Understanding and controlling the proton transfer process could be an effective strategy to improve OER performances. Herein, we present a strategy to accelerate the deprotonation of OER intermediates by introducing strong Brønsted acid sites (e.g. tungsten oxides, WOx) into the RuO2. The Ru-W binary oxide is reported as a stable and active iridium-free acidic OER catalyst that exhibits a low overpotential (235 mV at 10 mA cm-2) and low degradation rate (0.014 mV h-1) over a 550-hour stability test. Electrochemical studies, in-situ near-ambient pressure X-ray photoelectron spectroscopy and density functional theory show that the W-O-Ru Brønsted acid sites are instrumental to facilitate proton transfer from the oxo-intermediate to the neighboring bridging oxygen sites, thus accelerating bridging-oxygen-assisted deprotonation OER steps in acidic electrolytes. The universality of the strategy is demonstrated for other Ru-M binary metal oxides (M = Cr, Mo, Nb, Ta, and Ti).

Fast Near-Infrared Photodetection Using III-V Colloidal Quantum Dots.

Colloidal quantum dots (CQDs) are promising materials for infrared (IR) light detection due to their tunable bandgap and their solution processing; however, to date, the time response of CQD IR photodiodes is inferior to that provided by Si and InGaAs. It is reasoned that the high permittivity of II-VI CQDs leads to slow charge extraction due to screening and capacitance, whereas III-Vs-if their surface chemistry can be mastered-offer a low permittivity and thus increase potential for high-speed operation. In initial studies, it is found that the covalent character in indium arsenide (InAs) leads to imbalanced charge transport, the result of unpassivated surfaces, and uncontrolled heavy doping. Surface management using amphoteric ligand coordination is reported, and it is found that the approach addresses simultaneously the In and As surface dangling bonds. The new InAs CQD solids combine high mobility (0.04 cm2 V-1 s-1 ) with a 4× reduction in permittivity compared to PbS CQDs. The resulting photodiodes achieve a response time faster than 2 ns-the fastest photodiode among previously reported CQD photodiodes-combined with an external quantum efficiency (EQE) of 30% at 940 nm.

Concentrated Ethanol Electrosynthesis from CO2 via a Porous Hydrophobic Adlayer.

Electrochemical CO2 reduction can convert waste emissions into dense liquid fuels compatible with existing energy infrastructure. High-rate electrocatalytic conversion of CO2 to ethanol has been achieved in membrane electrode assembly (MEA) electrolyzers; however, ethanol produced at the cathode is transported, via electroosmotic drag and diffusion, to the anode, where it is diluted and may be oxidized. The ethanol concentrations that result on both the cathodic and anodic sides are too low to justify the energetic and financial cost of downstream separation. Here, we present a porous catalyst adlayer that facilitates the evaporation of ethanol into the cathode gas stream and reduces the water transport, leading to a recoverable stream of concentrated ethanol. The adlayer is comprised of ethylcellulose-bonded carbon nanoparticles and forms a porous, electrically conductive network on the surface of the copper catalyst that slows the transport of water to the gas channel. We achieve the direct production of an ethanol stream of 12.4 wt %, competitive with the concentration of current industrial ethanol production processes.

Ternary Alloys Enable Efficient Production of Methoxylated Chemicals via Selective Electrocatalytic Hydrogenation of Lignin Monomers.

We explore the selective electrocatalytic hydrogenation of lignin monomers to methoxylated chemicals, of particular interest, when powered by renewable electricity. Prior studies, while advancing the field rapidly, have so far lacked the needed selectivity: when hydrogenating lignin-derived methoxylated monomers to methoxylated cyclohexanes, the desired methoxy group (-OCH3) has also been reduced. The ternary PtRhAu electrocatalysts developed herein selectively hydrogenate lignin monomers to methoxylated cyclohexanes-molecules with uses in pharmaceutics. Using X-ray absorption spectroscopy and in situ Raman spectroscopy, we find that Rh and Au modulate the electronic structure of Pt and that this modulating steers intermediate energetics on the electrocatalyst surface to facilitate the hydrogenation of lignin monomers and suppress C-OCH3 bond cleavage. As a result, PtRhAu electrocatalysts achieve a record 58% faradaic efficiency (FE) toward 2-methoxycyclohexanol from the lignin monomer guaiacol at 200 mA cm-2, representing a 1.9× advance in FE and a 4× increase in partial current density compared to the highest productivity prior reports. We demonstrate an integrated lignin biorefinery where wood-derived lignin monomers are selectively hydrogenated and funneled to methoxylated 2-methoxy-4-propylcyclohexanol using PtRhAu electrocatalysts. This work offers an opportunity for the sustainable electrocatalytic synthesis of methoxylated pharmaceuticals from renewable biomass.

Bright and Stable Light-Emitting Diodes Based on Perovskite Quantum Dots in Perovskite Matrix.

Light-emitting diodes (LEDs) based on metal halide perovskite quantum dots (QDs) have achieved impressive external quantum efficiencies; however, the lack of surface protection of QDs, combined with efficiency droop, decreases device operating lifetime at brightnesses of interest. The epitaxial incorporation of QDs within a semiconducting shell provides surface passivation and exciton confinement. Achieving this goal in the case of perovskite QDs remains an unsolved challenge in view of the materials' chemical instability. Here, we report perovskite QDs that remain stable in a thin layer of precursor solution of perovskite, and we use strained QDs as nucleation centers to drive the homogeneous crystallization of a perovskite matrix. Type-I band alignment ensures that the QDs are charge acceptors and radiative emitters. The new materials show suppressed Auger bi-excition recombination and bright luminescence at high excitation (600 W cm-2), whereas control materials exhibit severe bleaching. Primary red LEDs based on the new materials show an external quantum efficiency of 18%, and these retain high performance to brightnesses exceeding 4700 cd m-2. The new materials enable LEDs having an operating half-life of 2400 h at an initial luminance of 100 cd m-2, representing a 100-fold enhancement relative to the best primary red perovskite LEDs.

Semiconductor quantum dots: Technological progress and future challenges.

In quantum-confined semiconductor nanostructures, electrons exhibit distinctive behavior compared with that in bulk solids. This enables the design of materials with tunable chemical, physical, electrical, and optical properties. Zero-dimensional semiconductor quantum dots (QDs) offer strong light absorption and bright narrowband emission across the visible and infrared wavelengths and have been engineered to exhibit optical gain and lasing. These properties are of interest for imaging, solar energy harvesting, displays, and communications. Here, we offer an overview of advances in the synthesis and understanding of QD nanomaterials, with a focus on colloidal QDs, and discuss their prospects in technologies such as displays and lighting, lasers, sensing, electronics, solar energy conversion, photocatalysis, and quantum information.

Ligand Exchange at a Covalent Surface Enables Balanced Stoichiometry in III-V Colloidal Quantum Dots.

III-V colloidal quantum dots (CQDs) are promising semiconducting materials for optoelectronic applications; however, their strong covalent character requires a distinct approach to surface management compared with widely investigated II-VI and IV-VI CQDs-dots, which by contrast are characterized by an ionic nature. Here we show stoichiometric reconstruction in InAs CQDs by ligand exchange. In particular, we find that indium-carboxylate ligands, which passivate as-synthesized InAs CQDs and are responsible for In-rich surfaces, can be replaced by anionic ligands such as thiols. This enables the production of inks consisting of balanced-stoichiomety CQDs; this is distinct from what is observed in II-VI and IV-VI CQDs, in which thiols replace carboxylates. The approach enables the implementation of InAs CQD solids as the active layer in photodiode detectors that exhibit an external quantum efficiency of 36% at 930 nm and a photoresponse time of 65 ns, which is 4 times shorter than that of reference PbS CQD devices.

Facet-Oriented Coupling Enables Fast and Sensitive Colloidal Quantum Dot Photodetectors.

Charge carrier transport in colloidal quantum dot (CQD) solids is strongly influenced by coupling among CQDs. The shape of as-synthesized CQDs results in random orientational relationships among facets in CQD solids, and this limits the CQD coupling strength and the resultant performance of optoelectronic devices. Here, colloidal-phase reconstruction of CQD surfaces, which improves facet alignment in CQD solids, is reported. This strategy enables control over CQD faceting and allows demonstration of enhanced coupling in CQD solids. The approach utilizes post-synthetic resurfacing and unites surface passivation and colloidal stability with a propensity for dots to couple via (100):(100) facets, enabling increased hole mobility. Experimentally, the CQD solids exhibit a 10× increase in measured hole mobility compared to control CQD solids, and enable photodiodes (PDs) exhibiting 70% external quantum efficiency (vs 45% for control devices) and specific detectivity, D* > 1012  Jones, each at 1550 nm. The photodetectors feature a 7 ns response time for a 0.01 mm2 area-the fastest reported for solution-processed short-wavelength infrared PDs.

CO2 electrolysis to multicarbon products in strong acid.

Carbon dioxide electroreduction (CO2R) is being actively studied as a promising route to convert carbon emissions to valuable chemicals and fuels. However, the fraction of input CO2 that is productively reduced has typically been very low, <2% for multicarbon products; the balance reacts with hydroxide to form carbonate in both alkaline and neutral reactors. Acidic electrolytes would overcome this limitation, but hydrogen evolution has hitherto dominated under those conditions. We report that concentrating potassium cations in the vicinity of electrochemically active sites accelerates CO2 activation to enable efficient CO2R in acid. We achieve CO2R on copper at pH <1 with a single-pass CO2 utilization of 77%, including a conversion efficiency of 50% toward multicarbon products (ethylene, ethanol, and 1-propanol) at a current density of 1.2 amperes per square centimeter and a full-cell voltage of 4.2 volts.

Dopant-Assisted Matrix Stabilization Enables Thermoelectric Performance Enhancement in n-Type Quantum Dot Films.

Efficient thermoelectric generators require further progress in developing n-type semiconductors that combine low thermal conductivity with high electrical conductivity. By embedding colloidal quantum dots (CQDs) in a metal halide matrix (QDMH), the metal halide matrix can enhance phonon scattering, thus suppressing thermal transport; however, simultaneously achieving high electrical conductivity in such systems has previously been limited by the deleterious impact of a large density of interfaces on charge transport. Therefore, new strategies are needed to improve charge carrier transport without sacrificing matrix-enabled low thermal transport. Here, we report the use of chemical doping in the solution state to improve electron transport while maintaining low thermal transport in QDMH films. By incorporating cesium carbonate (Cs2CO3) salts as a dopant prior to matrix formation, we find that the dopant stabilizes the matrix in colloidal inks and enables efficient n-type doping in QDMH films. As a result, this strategy leads to an enhanced n-type thermoelectric behavior in solution-processed QDMH films near room temperature, with a thermal conductivity of 0.25 W m-1 K-1-significantly lower than in prior films based on organic-ligand-cross-linked CQD films (>0.6 W m-1 K-1) and spark-plasma-sintered CQD systems (>1 W m-1 K-1). This study provides a pathway to developing efficient n-type thermoelectric materials with low thermal conductivity using single-step deposition and low-temperature processing.

Monolithic Organic/Colloidal Quantum Dot Hybrid Tandem Solar Cells via Buffer Engineering.

Monolithically integrated hybrid tandem solar cells (TSCs) that combine solution-processed colloidal quantum dot (CQD) and organic molecules are a promising device architecture, able to complement the absorption across the visible to the infrared. However, the performance of organic/CQD hybrid TSCs has not yet surpassed that of single-junction CQD solar cells. Here, a strategic optical structure is devised to overcome the prior performance limit of hybrid TSCs by employing a multibuffer layer and a dual near-infrared (NIR) absorber. In particular, a multibuffer layer is introduced to solve the problem of the CQD solvent penetrating the underlying organic layer. In addition, the matching current of monolithic TSCs is significantly improved to 15.2 mA cm-2 by using a dual NIR organic absorber that complements the absorption of CQD. The hybrid TSCs reach a power conversion efficiency (PCE) of 13.7%, higher than that of the corresponding individual single-junction cells, representing the highest efficiency reported to date for CQD-based hybrid TSCs.

Ligand-Assisted Reconstruction of Colloidal Quantum Dots Decreases Trap State Density.

Increasing the power conversion efficiency (PCE) of colloidal quantum dot (CQD) solar cells has relied on improving the passivation of CQD surfaces, enhancing CQD coupling and charge transport, and advancing device architecture. The presence of hydroxyl groups on the nanoparticle surface, as well as dimers-fusion between CQDs-has been found to be the major source of trap states, detrimental to optoelectronic properties and device performance. Here, we introduce a CQD reconstruction step that decreases surface hydroxyl groups and dimers simultaneously. We explored the dynamic interaction of charge carriers between band-edge states and trap states in CQDs using time-resolved spectroscopy, showing that trap to ground-state recombination occurs mainly from surface defects in coupled CQD solids passivated using simple metal halides. Using CQD reconstruction, we demonstrate a 60% reduction in trap density and a 25% improvement in charge diffusion length. These translate into a PCE of 12.5% compared to 10.9% for control CQDs.

A Chemically Orthogonal Hole Transport Layer for Efficient Colloidal Quantum Dot Solar Cells.

Colloidal quantum dots (CQDs) are of interest in light of their solution-processing and bandgap tuning. Advances in the performance of CQD optoelectronic devices require fine control over the properties of each layer in the device materials stack. This is particularly challenging in the present best CQD solar cells, since these employ a p-type hole-transport layer (HTL) implemented using 1,2-ethanedithiol (EDT) ligand exchange on top of the CQD active layer. It is established that the high reactivity of EDT causes a severe chemical modification to the active layer that deteriorates charge extraction. By combining elemental mapping with the spatial charge collection efficiency in CQD solar cells, the key materials interface dominating the subpar performance of prior CQD PV devices is demonstrated. This motivates to develop a chemically orthogonal HTL that consists of malonic-acid-crosslinked CQDs. The new crosslinking strategy preserves the surface chemistry of the active layer beneath, and at the same time provides the needed efficient charge extraction. The new HTL enables a 1.4× increase in charge carrier diffusion length in the active layer; and as a result leads to an improvement in power conversion efficiency to 13.0% compared to EDT standard cells (12.2%).