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Non-toxic and rapid chemical bath deposition for SnO2 electron transporting layers in perovskite solar cells
No full textPerovskite solar cells are a promising new solar technology with efficiencies surpassing polycrystalline silicon solar cell technology. For the n-i-p perovskite solar cells, tin oxide is typically used as the electron transport layer. One typical deposition method is chemical bath deposition. However, the drawbacks are toxic precursors and the slow reaction driven by dissolved oxygen forming SnO2 x. Here, we present a tin oxide chemical bath deposition starting from non-toxic sodium stannate solutions. Within 6 minutes of reaction time, a 9 nm thick amorphous Sn(IV)-oxide film is grown yielding solar cells with power conversion efficiencies of at least 23.2%. Surprisingly, the sole use of Sn(IV) precursors contradicts the previous Sn(II) doping assumption required for n-doping & high electric conductivity, and, unexpectedly, amorphous tin oxide films are as suitable for charge transport layers as their crystalline counterparts. The synthesis method is transferrable to other substrates (ITO, glass) and other thin-film metal oxide coatings (MoOx, SiO2) and beneficial for devices such as solar cells, photodetectors, light emitting diodes, and heterogeneous catalysis
Environment- and Conformation-Induced Frequency Shifts of C–D Vibrational Stark Probes in NAD(P)H Cofactors
No full textNAD(P)H cofactors are found in all forms of life and are essential for electron and hydrogen atom transfer. The linear response of a carbon-deuterium (C–D) vibration based on the vibrational Stark effect can facilitate measurements of electric fields for critical biological reactions including cofactor-mediated hydride transfer. We find both inter- and intramolecular electric fields influence the C–D frequency in NAD(P)H and nicotinamide-like models where the reactive C4-hydrogen has been deuterated. Hence, the C–D frequency can report both environmental electrostatics and conformational changes of the nicotinamide ring. Conformation-dependent effects are mediated through space as electrostatic effects, rather than through-bond. A Stark tuning rate of ~0.57 cm-1/(MV/cm) was determined using both experimental and computational approaches, including vibrational solvatochromism, molecular dynamics simulations, and in-silico Stark calculations. The vibrational probe’s Stark tuning rate is shown to be robust and suitable for measuring fields along hydride transfer reaction coordinates in enzyme
A Comparative Study of Hydrogen-Rich Gas Production from Gasification of Three Agricultural Feedstocks
No full textThis study comparatively investigated the hydrogen-rich gas generation profiles from agricultural feedstocks (Zea mays stalk, Arundo donax rhizome, and Arachis hypogaea husk) through gasification or pyrolysis-gasification process. The hydrogen production efficiency and the output of CO were evaluated under varying gasification conditions, including temperatures from 800°C to 1100°C and steam supplies from 1 mL/min to 5 mL/min. Pyrolyzed feedstocks can rapidly (0.60 L/min) release hydrogen at a gasification temperature of 900°C with 5 mL/min of steam supply. Furthermore, increasing the pyrolysis temperature does not decrease hydrogen production, while pyrolyzed feedstocks show a higher hydrogen output (an increase of 1.64% to 10.36%) compared to those that have not undergone pyrolysis pretreatment. The novelty of the present study includes 1) the comparison of hydrogen generation efficiency from pyrolyzed or non-pyrolyzed feedstocks and 2) the investigation of the generation profiles of syngas and the hydrogen releasing rate from feedstock gasification under various conditions
Hydrogen bond blueshifts in nitrile vibrational spectra are dictated by hydrogen bond geometry and dynamics
No full textVibrational Stark effect (VSE) spectroscopy has become one of the most important experimental approaches to determine the strength of noncovalent, electrostatic interactions in chemistry and biology and to quantify their influence on structure and reactivity. Nitriles (C≡N) have been widely used as VSE probes, but their application has been complicated by an anomalous hydrogen bond (HB) blueshift which is not encompassed within the VSE framework. We present an empirical model describing the anomalous HB blueshift in terms of H-bonding geometry, i.e. as a function of HB distance and angle with respect to the C≡N group. This model is obtained by comparing vibrational observables from density functional theory and electrostatics from the polarizable AMOEBA force field, and it provides a physical explanation for the HB blueshift in terms of underlying multipolar and Pauli repulsion contributions. Additionally, we compare predicted blueshifts with experimental results and find our model provides a useful, direct framework to analyze HB geometry for rigid HBs, such as within proteins or chemical frameworks. In contrast, nitriles in highly dynamic H-bonding environments like protic solvents are no longer a function solely of geometry; this is a consequence of motional narrowing, which we demonstrate by simulating IR spectra. Overall, when HB geometry and dynamics are accounted for, an excellent correlation is found between observed and predicted HB blueshifts. This correlation includes different types of nitriles and HB donors, suggesting that our model is general and can aid in understanding HB blueshifts wherever nitriles can be implemented
A framework for optimisation and techno-economic analysis of CO2 pressurisation strategies for pipeline transportation
No full text– This paper presents a framework for optimisation and techno-economic analysis of various pressurisation pathways for CO2 pipeline transportation. The pressurisation pathways include a conventional compression only case from initial to final pressure, a sub-critical compression part followed by cooling, liquefaction and pumping and also a super-critical compression part followed by cooling and dense phase pumping. The presented framework is developed based on open-source components and information available in the public domain. The framework includes a high level of flexibility to study variations in initial and final pressures, inclusion of inter-stage pressure drop, inter-stage cooling temperature, liquefaction/pumping pressure, among others. The implemented methods i.e. the thermodynamic and economic models applied, are rigorously validated and bench-marked against literature data. Contrary to former
studies that focus mainly on reduction of the work required for pressurisation, the presented method includes additional capabilities to assess CAPEX, OPEX and the levelised cost of CO2 compression. The analysis shows that in some cases the minimum levelised cost does not coincide with the minimum work. It is also demonstrated that for some cases the super-critical compression/cooling/pumping case and the sub-critical compression/cooling/liquefaction/pumping pathways provide optimal levelised cost compared to a multi-stage compression only case
Electrochemical Phase Interconversion Enables Homogeneous-Heterogeneous Bifunctionality in Pd-Catalyzed Vinyl Acetate Synthesis
No full textCurrent mechanistic paradigms in catalysis generally hold that a catalytic cycle is carried out by either a homogeneous or heterogeneous active species. Herein, we show that a prominent industrial process, palladium-catalyzed vinyl acetate synthesis, proceeds via interconversion of heterogeneous Pd(0) and homogeneous Pd(II) during catalysis, with each species playing a complementary role. Using electrochemical probes, we find that heterogeneous nanoparticulate Pd(0) serves as an active oxygen reduction electrocatalyst to furnish the high driving force required for corrosion to form homogeneous Pd(II), which then catalyzes selective ethylene acetoxylation with re-formation of heterogeneous Pd(0). Inhibiting the corrosion of Pd(0) to Pd(II) by galvanic protection results in reversible poisoning of catalysis, highlighting the essential role of phase conversion in this catalytic cycle. These results challenge the tacit assumption that catalysis proceeds via either homogeneous or heterogeneous modes, and instead highlights how dynamic phase interconversion can serve to harness and couple complementary reactivity across molecular and material active sites
Towards reliable oxidation state analysis of tin halide perovskites with XPS
No full textTin is the most promising replacement for lead in hybrid halide perovskite solar absorbers. A disadvantage of tin perovskites is ease of oxidation of Sn(II) hampering optoelectronic performance and long-term stability. Quantification of the extent of Sn oxidation in hybrid halide perovskites is therefore an important indicator of material stability but remains a significant challenge. X-ray photoemission spectroscopy (XPS) is commonly used to measure Sn chemical environments; we show here that conventional approaches to fitting the Sn 3d spectra from perovskite surfaces can easily lead to erroneous conclusions about the tin oxidation state. We consider several approaches to developing a robust fitting model for Sn 3d spectra. Furthermore, we identify that tin halide perovskite surfaces can be unstable under XPS measurement conditions, and the chemical state of tin will change significantly over typical analysis times. We use correlation analysis to validate our fitting model and identify phases present
Phenomenological observations of quinone-mediated zinc oxidation in an alkaline environment
No full textRedox-mediated electrochemistry is an area of growing interest, particularly in the context of energy storage. The development of such systems requires knowledge of underlying reaction mechanisms, which bear similarities to the processes that underpin corrosion and semiconductor electrochemistry. Herein we discuss an example system, quinone-mediated zinc oxidation in an alkaline environment, using knowledge from the corrosion and semiconductor fields to understand the phenomenological aspects of the reaction
Meta-analysis of permeability literature data shows possibilities and limitations of popular methods
No full textPermeability is an important molecular property in drug discovery, as it co-determines pharmacokinetics whenever a drug crosses the phospholipid bilayer, e.g., into the cell, in the gastrointestinal tract or across the blood-brain barrier. Many methods for the determination of permeability have been developed, including cell line assays, cell-free model systems like PAMPA mimicking, e.g., gastrointestinal epithelia or the skin, as well as the Black lipid membrane (BLM) and sub-micrometer liposomes. Furthermore, many in silico approaches have been developed for permeability prediction.
Meta-analysis of publicly available databases for permeability data (MolMeDB and ChEMBL) was performed to establish their usability. Firstly, experimental data can only be measured between thresholds for the lowest and highest permeation rate obtainable within physical boundaries. These thresholds vary strongly between methods. Secondly, computed data do not obey these thresholds but, on the other hand, can produce incorrect results. Thirdly, even for the same method and molecule, there is often a strong discrepancy between individual measured values. These differences are based not only on the statistics but also on the varying approaches and evaluation of the measured data. Thus, when working with in-house measured or published permeability data, we recommend to be cautious with their interpretation
Selective Inhibitor Design Against Thymidylate Synthase of Mycobacterium tuberculosis using Alchemical Simulations
No full textThymidylate synthase is an essential enzyme that catalyzes the conversion of deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP). Thymidylate synthase from Mycobacterium tuberculosis (MtbThyX) recognizes the deprotonated substrate dUMP(d) (ionized at N3, charge = -3) involving cationic side-chain of Arg199, whereas the human analog (hThyA) select the natural substrate dUMP (charge = -2) by involving polar side-chain of Asn226 in the binding pocket. Distinctly different protonation states of the substrate and the catalytic pocket architecture make MtbThyX an attractive drug target for combating Mycobacterium tuberculosis. Fluorodeoxyuridylate (FdUMP) is a known inhibitor of thymidylate synthase, which is severely limited by poor selectivity (more potent against hThyA relative to MtbThyX). Using FdUMP as a template, we designed three drug-like ligands, L1, L2, and L3, by (1) removing the proton from the Watson-Crick edge and (2) substituting the ketone/hydroxyl group by fluorine and or carboxylic moiety. The absence of a proton on the N3 atom of the ligand is intended to ensure selectivity by favoring MtbThyX binding (skipping the N3 ionization requirement) but penalizing hThyA binding (disrupting the interaction with Asn226). Ionization of the carboxyl group in the ligands was expected to increase the affinity in the cationic binding pocket of MtbThyX. Alchemical simulations confirmed that the designed ligands are strongly favored and disfavored relative to the substrate (dUMP) by MtbThyX and hThyA, respectively. In contrast to hThyA, the catalytic pocket of MtbThyX proved to be relatively dry and stabilized the relatively compact conformation of the ligand (which had a noticeable effect on the sugar puckering). Favorable protein-ligand electrostatic interaction in the dry MtbThyX pocket strongly favored ligand binding. In contrast, the interaction between the Watson-Crick edge of ligands and hThyA was compromised, resulting in water exposure. Ligand L2 is particularly advantageous for its highest affinity for MtbThyX and weak affinity for hThyA. The L2:MtbThyX complex is stabilized by a new salt-bridge interaction (COO- of L2…Arg107 of protein) and a bridging water molecule (between COO- of L2 and E92 of protein) in the binding pocket. Moreover, our estimated pKa of -8 unit of N3 (dUMP) in the MtbThyX catalytic pocket indicated the strong acidic nature of the uracil, corroborating previous experimental and computational claims. These findings provide insights into the protein-ligand binding affinity in atomic details and a rational approach for inhibitor design against MtbThyX