Compact Solid Electrolyte Interface Realization Employing Surface-Modified Fillers for Long-Lasting, High-Performance All-Solid-State Li-Metal Batteries.

The implementation of polymer-based Li-metal batteries is hindered by their low coulombic efficiency and poor cycling stability attributed to continuous electrolyte decomposition. Enhancement of the solid electrolyte interface (SEI) stability is key to mitigating electrolyte decomposition. This study proposes surface-functionalized silica mesoball fillers to fabricate a composite polymer electrolyte (MSBM-CPE). As a result of surface modification, the polyethylene oxide matrix benefits from the uniform distribution of the filler, which provides a large surface area and Lewis acid sites. Molecular dynamics simulations reveal that the dissociation energy of lithium bis(trifluoromethanesulfonyl)imide in the filler is fourfold higher (-1.95 eV) than that of the filler-free electrolyte. Consequently, the MSMB-CPE diffusivity is 30 times higher than its filler-free counterpart. The MSMB-CPE of ionic conductivity of 1.16 × 10-2 S cm-1 @60 °C and a venerable Li-ion transference number of 0.81. The excellent compatibility of MSMB-CPE with the Li anode is demonstrated by its stable symmetric cell performance under high current density (200 µA cm-2 @60 °C) for over 5000 h. Approximately 85.60% retention capacity of the [Li/MSMB-CPE/LiFePO4] full cell after 700 cycles. Furthermore, compositional analysis reveals that the SEI layer in MSMB-CPE is smooth with fewer by-products at the electrolyte/Li interface.

Remnant Copper Cation-Assisted Atom Mixing in Multicomponent Nanoparticles.

Nanostructured high-/medium-entropy compounds have emerged as important catalytic materials for energy conversion technologies, but complex thermodynamic relationships involved with the element mixing enthalpy have been a considerable roadblock to the formation of stable single-phase structures. Cation exchange reactions (CERs), in particular with copper sulfide templates, have been extensively investigated for the synthesis of multicomponent heteronanoparticles with unconventional structural features. Because copper cations within the host copper sulfide templates are stoichiometrically released with incoming foreign cations in CERs to maintain the overall charge balance, the complete absence of Cu cations in the nanocrystals after initial CERs would mean that further compositional variation would not be possible by subsequent CERs. Herin, we successfully retained a portion of Cu cations within the silver sulfide (Ag2S) and gold sulfide (Au2S) phases of Janus Cu2-xS-M2S (M = Ag, Au) nanocrystals after the CERs, by partially suppressing the transformation of the anion sublattice that inevitably occurs during the introduction of external cations. Interestingly, the subsequent CERs on Janus Cu1.81S-M2S (M = Ag, Au), by utilizing the remnant Cu cations, allowed the construction of Janus Cu1.81S-AgxAuyS, which preserved the initial heterointerface. The synthetic strategy described in this work to suppress the complete removal of the Cu cation from the template could fabricate the CER-driven heterostructures with greatly diversified compositions, which exhibit unusual optical and catalytic properties.

SABRE hyperpolarization of nicotinamide derivatives and their molecular dynamics properties.

Signal amplification by reversible exchange hyperpolarization explores the chemical structure and kinetic properties of nicotinamide derivatives. N-Benzyl nicotinamide and nicotinic acid hydrazide compounds display relatively fast dissociation rates of approximately 7-8 s-1 and long proton T1 relaxation times of 5-20 s, respectively. Consequently, these substrates exhibit remarkable signal enhancements, reaching approximately 175 and 102 fold, respectively, underscoring the efficacy of the hyperpolarization technique in elucidating the behavior of these compounds.

NbO2 a Highly Stable, Ultrafast Anode Material for Li- and Na-Ion Batteries.

Anode materials with fast charging capabilities and stability are critical for realizing next-generation Li-ion batteries (LIBs) and Na-ion batteries (SIBs). The present work employs a simple synthetic strategy to obtain NbO2 and studies its applications as an anode for LIB and SIB. In the case of the LIB, it exhibited a specific capacity of 344 mAh g-1 at 100 mA g-1. It also demonstrated remarkable stability over 1000 cycles, with 92% capacity retention. Additionally, it showed a unique fast charging capability, which takes 30 s to reach a specific capacity of 83 mAh g-1. For the SIB, NbO2 exhibited a specific capacity of 244 mAh g-1 at 50 mA g-1 and showed 70% capacity retention after 500 cycles. Furthermore, detailed density functional theory reveals that various factors like bulk and surface charging processes, lower ion diffusion energy barriers, and superior electronic conductivity of NbO2 are responsible for the observed battery performances.

Scaling-Up Insights for Zinc-Air Battery Technologies Realizing Reversible Zinc Anodes.

Zinc-air battery (ZAB) technology is considered one of the promising candidates to complement the existing lithium-ion batteries for future large-scale high-energy-storage demands. The scientific literature reveals many efforts for the ZAB chemistries, materials design, and limited accounts for cell design principles with apparently superior performances for liquid and solid-state electrolytes. However, along with the difficulty of forming robust solid-electrolyte interphases, the discrepancy in testing methods and assessment metrics severely challenges the realistic evaluation/comparison and commercialization of ZABs. Here, strategies to formulate reversible zinc anodes are proposed and specific cell-level energy metrics (100-500 Wh kg-1 ) and realistic long-cycling operations are realized. Stabilizing anode/electrolyte interfaces results in a cumulative capacity of 25 Ah cm-2 and Coulomb efficiency of >99.9% for 5000 plating/stripping cycles. Using 1-10 Ah scale (≈500 Wh kg-1 at cell level) solid-state zinc-air pouch cells, scale-up insights for Ah-level ZABs that can progress from lab-scale research to practical production are also offered.

Multicomponent Covalent Organic Framework Solid Electrolyte Allowing Effective Li-Ion Dissociation and Diffusion for All-Solid-State Batteries.

Organic solid electrolytes compatible with all-solid-state Li metal batteries (LMBs) are essential to ensuring battery safety, high energy density, and long-term cycling performance. However, it remains a challenge to develop an approach to provide organic solid electrolytes with capabilities for the facile dissociation of strong Li-ion pairs and fast transport of ionic components. Herein, a diethylene glycol-modified pyridinium covalent organic framework (DEG-PMCOF) with a well-defined periodic structure is prepared as a multicomponent solid electrolyte with a cationic moiety of high polarity, an additional flexible ion-transporter, and an ordered ionic channel for all-solid-state LMBs. The DEG-containing pyridinium groups of DEG-PMCOF allow a lower dissociation energy of Li salts and a smaller energy barrier of Li-ion transport, leading to high ion conductivity (1.71 × 10-4 S cm-1) and a large Li-ion transfer number (0.61) at room temperature in the solid electrolyte. The DEG-PMCOF solid electrolyte exhibits a wide electrochemical stability window and effectively suppresses the formation of Li dendrites and dead Li in all-solid-state LMBs. Molecular dynamics and density functional theory simulations provide insights into the mechanisms for the enhanced Li-ion transport driven by the integrated diffusion process based on hopping motion, vehicle motion, and free diffusion of DEG-PMCOF. The all-solid-state LMB assembled with a DEG-PMCOF solid electrolyte displays a high specific capacity with a retention of 99% and an outstanding Coulombic efficiency of 99% at various C-rates during long-term cycling. This DEG-PMCOF approach can offer an effective route to design various solid-state Li batteries.

Heterointerface promoted trifunctional electrocatalysts for all temperature high-performance rechargeable Zn-air batteries.

The rational design of wide-temperature operating Zn-air batteries is crucial for their practical applications. However, the fundamental challenges remain; the limitation of the sluggish oxygen redox kinetics, insufficient active sites, and poor efficiency/cycle lifespan. Here we present heterointerface-promoted sulfur-deficient cobalt-tin-sulfur (CoS1-δ/SnS2-δ) trifunctional electrocatalysts by a facile solvothermal solution-phase approach. The CoS1-δ/SnS2-δ displays superb trifunctional activities, precisely a record-level oxygen bifunctional activity of 0.57 V (E1/2 = 0.90 V and Ej=10 = 1.47 V) and a hydrogen evolution overpotential (41 mV), outperforming those of Pt/C and RuO2. Theoretical calculations reveal the modulation of the electronic structures and d-band centers that endorse fast electron/proton transport for the hetero-interface and avoid the strong adsorption of intermediate species. The alkaline Zn-air batteries with CoS1-δ/SnS2-δ manifest record-high power density of 249 mW cm-2 and long-cycle life for >1000 cycles under harsh operations of 20 mA cm-2, surpassing those of Pt/C + RuO2 and previous state-of-the-art catalysts. Furthermore, the solid-state flexible Zn-air battery also displays remarkable performance with an energy density of 1077 Wh kg-1, >690 cycles for 50 mA cm-2, and a wide operating temperature from +80 to -40 °C with 85% capacity retention, which provides insights for practical Zn-air batteries.

An Ion-Channel-Restructured Zwitterionic Covalent Organic Framework Solid Electrolyte for All-Solid-State Lithium-Metal Batteries.

Organic solid electrolytes offer an effective route for safe and high-energy-density all-solid-state Li metal batteries. However, it remains a challenge to devise a new strategy to promote the dissociation of strong ion pairs and the transport of ionic components in organic solid electrolytes. Herein, a zwitterionic covalent organic framework (Zwitt-COF) with well-defined chemical and pore structures is prepared as a solid electrolyte capable of accelerating the dissociation and transport of Li ions. The Zwitt-COF solid electrolyte exhibits a high room-temperature ionic conductivity of 1.65 × 10-4  S cm-1 with a wide electrochemical stability window. Besides, the Zwitt-COF solid electrolyte displays stable Li plating/stripping behavior via effective inhibition of the formation of Li dendrites and dead Li, leading to superior long-term cycle performance with retention of 99% discharge capacity and 98% Coulombic efficiency in an all-solid-state Li-metal battery. Theoretical simulations reveal that the incorporation of zwitterionic groups into COF can facilitate the dissociation of strong ion pairs and reconstruct the AA-stacking configuration by dissociative adsorption of Li+ ions on Zwitt-COF producing linear hexagonal ion channels in the Zwitt-COF solid electrolyte. This strategy based on Zwitt-COF can provide an alternative way to construct various solid-state Li batteries.

A Universal Perovskite Nanocrystal Ink for High-Performance Optoelectronic Devices.

Semiconducting lead halide perovskite nanocrystals (PNCs) are regarded as promising candidates for next-generation optoelectronic devices due to their solution processability and outstanding optoelectronic properties. While the field of light-emitting diodes (LEDs) and photovoltaics (PVs), two prime examples of optoelectronic devices, has recently seen a multitude of efforts toward high-performance PNC-based devices, realizing both devices with high efficiencies and stabilities through a single PNC processing strategy has remained a challenge.  In this work, diphenylpropylammonium (DPAI) surface ligands, found through a judicious ab-initio-based ligand search, are shown to provide a solution to this problem. The universal PNC ink with DPAI ligands presented here, prepared through a solution-phase ligand-exchange process, simultaneously allows single-step processed LED and PV devices with peak electroluminescence external quantum efficiency of 17.00% and power conversion efficiency of 14.92% (stabilized output 14.00%), respectively. It is revealed that a careful design of the aromatic rings such as in DPAI is the decisive factor in bestowing such high performances, ease of solution processing, and improved phase stability up to 120 days. This work illustrates the power of ligand design in producing PNC ink formulations for high-throughput production of optoelectronic devices; it also paves a path for "dual-mode" devices with both PV and LED functionalities.

Supramolecular Polymer Intertwined Free-Standing Bifunctional Membrane Catalysts for All-Temperature Flexible Zn-Air Batteries.

Rational construction of flexible free-standing electrocatalysts featuring long-lasting durability, high efficiency, and wide temperature tolerance under harsh practical operations are fundamentally significant for commercial zinc-air batteries. Here, 3D flexible free-standing bifunctional membrane electrocatalysts composed of covalently cross-linked supramolecular polymer networks with nitrogen-deficient carbon nitride nanotubes are fabricated (referred to as PEMAC@NDCN) by a facile self-templated approach. PEMAC@NDCN demonstrates the lowest reversible oxygen bifunctional activity of 0.61 V with exceptional long-lasting durability, which outperforms those of commercial Pt/C and RuO2. Theoretical calculations and control experiments reveal the boosted electron transfer, electrolyte mass/ion transports, and abundant active surface site preferences. Moreover, the constructed alkaline Zn-air battery with PEMAC@NDCN air-cathode reveals superb power density, capacity, and discharge-charge cycling stability (over 2160 cycles) compared to the reference Pt/C + RuO2. Solid-state Zn-air batteries enable a high power density of 211 mW cm-2, energy density of 1056 Wh kg-1, stable charge-discharge cycling of 2580 cycles for 50 mA cm-2, and wide temperature tolerance from - 40 to 70 °C with retention of 86% capacity compared to room-temperature counterparts, illustrating prospects over harsh operations.

High-Alkaline Water-Splitting Activity of Mesoporous 3D Heterostructures: An Amorphous-Shell@Crystalline-Core Nano-Assembly of Co-Ni-Phosphate Ultrathin-Nanosheets and V- Doped Cobalt-Nitride Nanowires.

Introducing amorphous and ultrathin nanosheets of transition bimetal phosphate arrays that are highly active in the oxygen evolution reaction (OER) as shells over an electronically modulated crystalline core with low hydrogen absorption energy for an excellent hydrogen evolution reaction (HER) can boost the sluggish kinetics of the OER and HER in alkaline electrolytes. Therefore, in this study, ultrathin and amorphous cobalt-nickel-phosphate (CoNiPOx ) nanosheet arrays are deposited over vanadium (V)-doped cobalt-nitride (V3% -Co4 N) crystalline core nanowires to obtain amorphous-shell@crystalline-core mesoporous 3D-heterostructures (CoNiPOx @V-Co4 N/NF) as bifunctional electrocatalysts. The optimized electrocatalyst shows extremely low HER and OER overpotentials of 53 and 270 mV at 10 mA cm-2 , respectively. The CoNiPOx @V3% -Co4 N/NF (+/-) electrolyzer utilizing the electrocatalyst as both anode and cathode demonstrates remarkable overall water-splitting activity, requiring a cell potential of only 1.52 V at 10 mA cm-2 , 30 mV lower than that of the RuO2 /NF (+)/20%-Pt/C/NF (-) electrolyzer. Such impressive bifunctional activities can be attributed to abundant active sites, adjusted electronic structure, lower charge-transfer resistance, enhanced electrochemically active surface area (ECSA), and surface- and volume-confined electrocatalysis resulting from the synergistic effects of the crystalline V3% -Co4 N core and amorphous CoNiPOx shells boosting water splitting in alkaline media.

Structural and Electronic Modulations of Imidazolium Covalent Organic Framework-Derived Electrocatalysts for Oxygen Redox Reactions in Rechargeable Zn-Air Batteries.

Covalent organic frameworks (COFs) are promising candidates for the controllable design of electrocatalysts. However, bifunctional electrocatalytic activities for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remain challenging in COFs. In this study, imidazolium-rich COFs (IMCOFs) with well-defined active sites and characteristic three-dimensional assembly structures were readily prepared, and their electronic structures were tuned by Co incorporation to elicit bifunctional electrocatalytic activities for the ORR and OER. The Co nanoparticle-incorporated spherical IMCOF-derived electrocatalyst (CoNP-s-IMCOF) exhibited lower overpotentials for the ORR and OER compared with the atomic Co-incorporated planar IMCOF-derived electrocatalyst (Co-p-IMCOF). Computational simulations revealed that the imidazole carbon sites of CoNP-s-IMCOF rather than the triazine carbons were the active sites for the ORR and OER, and its p-band center downshifted via charge transfer, facilitating the chemisorption of oxygen intermediates during the reactions. A Zn-air battery with CoNP-s-IMCOF exhibited a small voltage gap of 1.3 V with excellent durability for 935 cycles. This approach for control over the three-dimensional assembly and electronic structures of IMCOFs can be extended to the development of diverse catalytic nanomaterials for applications of interest.

Guanidinium-Pseudohalide Perovskite Interfaces Enable Surface Reconstruction of Colloidal Quantum Dots for Efficient and Stable Photovoltaics.

Complete surface passivation of colloidal quantum dots (CQDs) and their strong electronic coupling are key factors toward high-performance CQD-based photovoltaics (CQDPVs). Also, the CQD matrices must be protected from oxidative environments, such as ambient air and moisture, to guarantee air-stable operation of the CQDPVs. Herein, we devise a complementary and effective approach to reconstruct the oxidized CQD surface using guanidinium and pseudohalide. Unlike conventional halides, thiocyanate anions provide better surface passivation with effective replacement of surface oxygen species and additional filling of defective sites, whereas guanidinium cations promote the construction of epitaxial perovskite bridges within the CQD matrix and augment electronic coupling. Additionally, we replace a defective 1,2-ethanedithiol-treated CQD hole transport layer (HTL) with robust polymeric HTLs, based on a judicious consideration of the energy level alignment established at the CQD/HTL interface. These efforts collectively result in high-performance and stable CQDPVs with photocurrents over 30 mA cm-2, ∼80% quantum efficiency at excitonic peaks and stable operation under humid and ambient conditions. Elucidation of carrier dynamics further reveals that interfacial recombination associated with band alignment governs both the CQDPV performance and stability.

Experimental and Theoretical Insights into the Borohydride-Based Reduction-Induced Metal Interdiffusion in Fe-Oxide@NiCo2O4 for Enhanced Oxygen Evolution.

The oxygen evolution reaction (OER) plays a key role in determining the performance of overall water splitting, while a core technological consideration is the development of cost-effective, efficient, and durable catalysts. Here, we demonstrate a robust reduced Fe-oxide@NiCo2O4 bilayered non-precious-metal oxide composite as a highly efficient OER catalyst in an alkaline medium. A bilayered oxide composite film with an interconnected nanoflake morphology (Fe2O3@NiCo2O4) is reduced in an aqueous NaBH4 solution, which results in a mosslike Fe3O4@NiCo2O4 (reduced Fe-oxide@NiCo2O4; rFNCO) nanostructured film with an enhanced electrochemical surface area. The rFNCO film demonstrates an outstanding OER activity with an extraordinary low overpotential of 189 mV at 10 mA cm-2 (246 mV at 100 mA cm-2) and a remarkably small Tafel slope of 32 mV dec-1. The film also shows excellent durability for more than 50 h of continuous operation, even at 100 mA cm-2. Furthermore, density functional theory calculations suggest that the unintentionally in situ doped Ni during the reduction reaction possibly improves the OER performance of the rFNCO catalyst shifting d-band centers of both Fe and Ni active sites.

Unveiling the effect of the crystalline phases of iron oxyhydroxide for highly sensitive and selective detection of dopamine.

Electrocatalysis is key to the development of several important energy and biosensing applications. In this regard, the crystalline phase-dependent electrocatalytic activity of materials has been extensively studied for reactions such as hydrogen evolution, oxygen reduction, etc. But such comprehensive studies for evaluating the phase-dependence of electrochemical biosensing have not been undertaken. Herein, three crystalline phases (α-, ß-, and γ-) of iron oxyhydroxide (FeOOH) have been synthesized and characterized by spectroscopic and microscopy techniques. Electrochemical studies revealed their high sensitivity and selectivity towards dopamine (DA) detection. Amongst the three electrocatalysts, ß-FeOOH shows the highest sensitivity (337.15 µA mM-1 cm-2) and the lowest detection limit (0.56 µM). The enhanced electrocatalytic activity of ß-FeOOH, as compared to that of α- and γ-FeOOH, was attributed to its higher active site percentage and facile electrode kinetics. Furthermore, theoretical studies probed into the DA-FeOOH interactions by evaluating the charge transfer characteristics and hydrogen adsorption energies of the three phases to support the experimental findings.

Hybridisation of perovskite nanocrystals with organic molecules for highly efficient liquid scintillators.

Compared with solid scintillators, liquid scintillators have limited capability in dosimetry and radiography due to their relatively low light yields. Here, we report a new generation of highly efficient and low-cost liquid scintillators constructed by surface hybridisation of colloidal metal halide perovskite CsPbA3 (A: Cl, Br, I) nanocrystals (NCs) with organic molecules (2,5-diphenyloxazole). The hybrid liquid scintillators, compared to state-of-the-art CsI and Gd2O2S, demonstrate markedly highly competitive radioluminescence quantum yields under X-ray irradiation typically employed in diagnosis and treatment. Experimental and theoretical analyses suggest that the enhanced quantum yield is associated with X-ray photon-induced charge transfer from the organic molecules to the NCs. High-resolution X-ray imaging is demonstrated using a hybrid CsPbBr3 NC-based liquid scintillator. The novel X-ray scintillation mechanism in our hybrid scintillators could be extended to enhance the quantum yield of various types of scintillators, enabling low-dose radiation detection in various fields, including fundamental science and imaging.

Frustrated Lewis pairs with thermally activated delayed fluorescence properties: activation of formaldehyde.

Activation of formaldehyde (FA) by frustrated Lewis pairs (FLPs) that are comprised of bulky phosphines having a carbazolyl donor-triarylboryl acceptor unit and B(C6F5)3 led to the formation of FLP-FA adducts that exhibit a thermally activated delayed fluorescence.

Complementary Hybrid Semiconducting Superlattices with Multiple Channels and Mutual Stabilization.

An organic-inorganic hybrid superlattice with near perfect synergistic integration of organic and inorganic constituents was developed to produce properties vastly superior to those of either moiety alone. The complementary hybrid superlattice is composed of multiple quantum wells of 4-mercaptophenol organic monolayers and amorphous ZnO nanolayers. Within the superlattice, multichannel formation was demonstrated at the organic-inorganic interfaces to produce an excellent-performance field effect transistor exhibiting outstanding field-effect mobility with band-like transport and steep subthreshold swing. Furthermore, mutual stabilizations between organic monolayers and ZnO effectively reduced the performance degradation notorious in exclusively organic and ZnO transistors.

Donor-Acceptor-Appended Triarylboron Lewis Acids: Ratiometric or Time-Resolved Turn-On Fluorescence Response toward Fluoride Binding.

Triarylboron Lewis acid compounds (CzmBoT (1c) and DPAmBoT (2c)), in which carbazole (Cz) or diphenylamine (DPA) donors are linked with a triazine acceptor in the ortho position of the phenylene ring are prepared and characterized. The treatment of 1c and 2c with the fluoride anion produces the corresponding fluoride adducts [1cF]- and [2cF]- as a tetraethylammonium salt. An X-ray diffraction study of [1cF]- reveals a twisted conformation between the Cz and phenylene rings. The Cz-containing 1c shows a ratiometric fluorescence change upon fluoride binding, while the DPA-containing 2c exhibits a turn-on fluorescence response in tetrahydrofuran. In particular, both fluoride adducts exhibit thermally activated delayed fluorescence (TADF) properties with microsecond-range lifetimes. Electrochemical and theoretical analysis suggests that the intramolecular charge-transfer transition from the donor to a conjugated acceptor fragment is switched to the donor to a triazine transition after fluoride binding. Theoretical analysis further demonstrates the twisted structure, effective highest occupied molecular orbital-lowest unoccupied molecular orbital separation, and the small energy splitting between the excited singlet and triplet states for the fluoride adducts, with all supporting the observed TADF. The time-resolved fluorescence measurements of 2c in the presence of both fluoride and a competitive fluorescent dye (Coumarin 6) effectively eliminate the short-lived fluorescence of a dye, retaining long-lived fluorescence signals originating only from [2cF]-.

Role of Transition Metals in Layered Double Hydroxides for Differentiating the Oxygen Evolution and Nonenzymatic Glucose Sensing.

Layered double hydroxides (LDH) belong to the class of two-dimensional materials having a wide variety of applications ranging from energy storage to catalysis. Often, these materials when used for nonenzymatic electrochemical glucose sensing tend to be interfering with oxygen evolution reaction (OER), resulting in overestimation of the glucose. Herein, to address this, NiFe-based LDH were selected because of their ability to vary the metal ratios. The synthesized LDH have been characterized using various spectroscopic and microscopic techniques. Among the LDH synthesized, Ni4Fe-LDH have been able to differentiate the glucose oxidation potential and the onset potential of OER with minimum interference. The Ni4Fe-LDH sensor shows a sensitivity of 20.43 µA mM-1 cm-2 in the linear range of 0-4 mM concentrations. To further enhance the sensitivity, composites of reduced graphene oxide (rGO) have been synthesized in situ, and the Ni4Fe/rGO5 composites have shown an increased sensitivity of 176.8 µA mM-1 cm-2 attributed to the charge-transfer interactions. To understand the experimental observations, detailed computational studies have been carried out to study the effect of the electronic structure on the metal ratios of the LDH and its role in differentiating glucose sensing and the oxygen evolution reaction. Along with this, theoretical calculations are also carried out on LDH-graphene composites to study the charge-transfer interactions.