### Recent Submissions

• #### Study of the Effect of Research Octane Number on the Auto-Ignition of Lubricant Oil Surrogates (n-Hexadecane)

(ACS Omega, American Chemical Society (ACS), 2022-01-12) [Article]
Engine oil is considered one of the sources for pre-ignition in downsized boosted direct injection spark-ignited engines. When interacting with fuel sprayed in the combustion chamber, engine oil forms an ignitable mixture and can cause an ignition event before firing the spark plug. Because high research octane number (RON) fuels are difficult to auto-ignite and tend to suppress the knock in an internal combustion engine, studying their interaction with engine oil is essential. Hence, in the current study, a suitable lubricant oil surrogate, namely, n-hexadecane, is mixed with iso-octane and n-heptane at different concentrations to investigate the auto-ignition behavior at elevated pressures. Five sets of fuels (PRF0, PRF20, PRF50, PRF80, and PRF100) were prepared to get a wide range of RONs and blended with n-hexadecane at 15, 25, 35, and 45% mixture concentrations (vol %). These experiments were conducted in a constant volume combustion chamber, keeping the initial temperature constant at 300 °C. A single droplet of the mixture was suspended on a thermocouple bead to record the droplet’s lifetime temperature. It was observed that hexadecane mixed with PRF0, PRF20, PRF50, and PRF80 showed similar auto-ignition behaviors. The time of ignition (TI) for these mixtures initially increased until 25% concentration of the fuel in n-hexadecane, and further addition of fuels to 35% and higher concentrations showed a gradual decrease in TI. Ignition of mixtures with 35% and 45% fuel concentrations is attributed to n-heptane, as its low temperature chemistry is the dominant factor in its high reactivity compared to iso-octane. TI increased with the increasing concentration of PRF100 mixtures in hexadecane, unlike other PRF fuels tested in this study. This is because iso-octane is a high RON fuel with a higher auto-ignition temperature, making it challenging to auto-ignite.
• #### Using Triethylborane to Manipulate Reactivity Ratios in Epoxide-Anhydride Copolymerization: Application to the Synthesis of Polyethers with Degradable Ester Functions

(Molecules, MDPI AG, 2022-01-11) [Article]
The anionic ring-opening copolymerization (ROCOP) of epoxides, namely of ethylene oxide (EO), with anhydrides (AH) generally produces strictly alternating copolymers. With triethylborane (TEB)-assisted ROCOP of EO with AH, statistical copolymers of high molar mass including ether and ester units could be obtained. In the presence of TEB, the reactivity ratio of EO (rEO), which is normally equal to 0 in its absence, could be progressively raised to values lower than 1 or higher than 1. Conditions were even found to obtain rEO equal or close to 1. Samples of P(EO-co-ester) with minimal compositional drift could be synthesized; upon basic degradation of their ester linkages, these samples afforded poly(ethylene oxide) (PEO) diol samples of narrow molar mass distribution. In other cases where rEO were lower or higher than 1, the PEO diol samples eventually isolated after degradation exhibited a broader distribution of molar masses because of the compositional drift of initial P(EO-co-ester) samples.
• #### Air-Processable and Thermally Stable Hole Transport Layer for Non-Fullerene Organic Solar Cells

(ACS Applied Energy Materials, American Chemical Society (ACS), 2022-01-10) [Article]
Power conversion efficiencies (PCEs) of organic solar cells (OSCs) have now surpassed 19%. This has led to an increased focus on developing devices using methods and materials that are scalable, processable under ambient air atmospheres, and stable. However, current materials fall short of the essential requirements for stability and processability needed for cost-effective large-scale fabrication of high-performing OSCs. Here, we report a hybrid solution-processable hole transport layer (HTL) based on tantalum-doped tungsten oxide (TaWOx) nanoparticles and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) demonstrating good wettability over the hydrophobic active layer. N-i-p-type OSCs that are processed fully under ambient conditions, based on a polymer donor and a non-fullerene acceptor incorporating a combined TaWOx-PEDOT:PSS layer as HTL deliver a power conversion efficiency of 8.6%. OSCs utilizing the TaWOx-PEDOT:PSS HTL demonstrate improved thermal stability compared to devices based on the previously reported solution-processed MoOx-PEDOT:PSS HTL, which was found to severely degrade upon thermal treatment at 85 °C. Photoelectron spectroscopy and secondary ion mass spectrometry (SIMS) reveal that the MoOx-PEDOT:PSS HTL is prone to thermally induced intermixing with the underlying active layer, resulting in unfavorable changes in the interfacial energetics. No significant heat-induced changes are observed in the case of the TaWOx-PEDOT:PSS HTL when annealed up to 120 °C, imparting enhanced thermal stability to the devices. Improved wettability on hydrophobic surfaces, combined with air processability and enhanced thermal stability makes TaWOx-PEDOT:PSS a promising HTL material for fabricating stable NFA solar cells using roll-to-roll compatible printing and coating methods.
• #### A Universal Co-Solvent Evaporation Strategy Enables Direct Printing of Perovskite Single Crystals for Optoelectronic Device Applications

Solution-processed metal halide perovskite single crystals (SCs) are in high demand for a growing number of emerging device applications due to their superior optoelectronic properties compared to polycrystalline thin films. However, the historical focus on thin film optoelectronic and photovoltaic devices explains the absence of methods suitable for facile, scalable and high throughput fabrication of precision-engineered and positioned SCs and arrays. Here, we present a universal co-solvent evaporation (CSE) strategy by which perovskite SCsand arrays are produced directly on substrates from individual drying droplets in a single step within minutes at room temperature. The CSE strategy successfully guides supersaturation of drying droplets to suppress all unwanted crystallization pathways and is shown to produce SCsof a wide variety of three-dimensional (3D), quasi-two dimensional (2D), and mixed cation/halideperovskites. The drying droplet approach works with commonly used solvents, making it universal. Importantly, the CSE strategy ensures the SC consumes the precursor in its entirety, leaving little to no residue on substrates, which is crucial for enabling fabrication of SC arrays on large areas via printing and coating techniques. We go on to demonstrate direct on-chip fabrication of 3D and quasi-2D perovskite photodetector devices with outstanding performance. Our approach shows that metal halide perovskite SCs can now be produced on substrates from a drying solution via a wide range of solution processing methods, including microprinting and scalable, high throughput coating methods.
• #### Porous Ti3C2Tx MXene Membranes for Highly Efficient Salinity Gradient Energy Harvesting

(ACS Nano, American Chemical Society (ACS), 2022-01-09) [Article]
Extracting osmotic energy through nanoporous membranes is an efficient way to harvest renewable and sustainable energy using the salinity gradient between seawater and river water. Despite recent advances of nanopore-based membranes, which have revitalized the prospect of blue energy, their energy conversion is hampered by nanomembrane issues such as high internal resistance or low selectivity. Herein, we report a lamellar-structured membrane made of nanoporous Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> MXene sheets, exhibiting simultaneous enhancement in permeability and ion selectivity beyond their inherent trade-off. The perforated nanopores formed by facile H<sub>2</sub>SO<sub>4</sub> oxidation of the sheets act as a network of cation channels that interconnects interplanar nanocapillaries throughout the lamellar membrane. The constructed internal nanopores lower the energy barrier for cation passage, thereby boosting the preferential ion diffusion across the membrane. A maximum output power density of the nanoporous Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> MXene membranes reaches up to 17.5 W·m<sup>-2</sup> under a 100-fold KCl gradient at neutral pH and room temperature, which is as high as by 38% compared to that of the pristine membrane. The membrane design strategy employing the nanoporous two-dimensional sheets provides a promising approach for ion exchange, osmotic energy extraction, and other nanofluidic applications.
• #### Focusing and defocusing of tropical cyclone generated waves by ocean current refraction

(Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), 2022-01-07) [Article]
Waves generated by tropical cyclones can have devastating effects on coastal regions. However, the role of ocean currents in modifying wave amplitudes, wavelengths, and directions is commonly overlooked in wave forecasts, despite the fact that these interactions can lead to extreme wave conditions. Here, we use satellite observations and wave modeling to quantify the effects of ocean currents on the surface waves generated during a tropical cyclone event in the Arabian Sea. As a case study, this paper documents beams of wave heights originating from the eyewall of a tropical cyclone caused by current-induced refraction. Alternating regions of high and low wave heights in the model simulations are consistent with observations and extend for thousands of kilometers all the way to 100 m isobath. Our results highlight the importance of accounting for wave refraction by currents in order to accurately predict the impact of tropical cyclone generated waves on coastal regions.
• #### Scalable CMOS-BEOL compatible AlScN/2D Channel FE-FETs

(arXiv, 2022-01-06) [Preprint]
Intimate integration of memory devices with logic transistors is a frontier challenge in computer hardware. This integration is essential for augmenting computational power concurrently with enhanced energy efficiency in big-data applications such as artificial intelligence. Despite decades of efforts, reliable, compact, energy efficient and scalable memory devices are elusive. Ferroelectric Field Effect Transistors (FE-FETs) are a promising candidate but their scalability and performance in a back-end-of-line (BEOL) process remain unattained. Here, we present scalable BEOL compatible FE-FETs using two-dimensional (2D) MoS2 channel and AlScN ferroelectric dielectric. We have fabricated a large array of FE-FETs with memory windows larger than 7.8 V, ON/OFF ratios of greater than 10^7, and ON current density greater than 250 uA/um, all at ~80 nm channel lengths. Our devices show stable retention up to 20000 secs and endurance up to 20000 cycles in addition to 4-bit pulse programmable memory features thereby opening a path towards scalable 3D hetero-integration of 2D semiconductor memory with Si CMOS logic.
• #### Operando Monitoring and Deciphering the Structural Evolution in Oxygen Evolution Electrocatalysis

(Advanced Energy Materials, Wiley, 2022-01-05) [Article]
The oxygen evolution reaction (OER) acts as the bottleneck of some crucial energy conversion and storage technologies involving water electrolysis, CO2 electrolysis, and metal-air batteries, among others. The challenging sluggish reaction kinetics of the OER can be overcome via developing highly efficient electrocatalysts, which experience a dynamic structural evolution process during the reaction. However, the reaction mechanism of the structural transformation of electrocatalysts during the OER and the structure-activity correlation in understanding the real active sites remain elusive. Fortunately, operando characterizations offer a platform to study the structural evolution processes and the reaction mechanisms of OER electrocatalysts. In this review, using several in situ/operando techniques some recent advances are elaborated with emphases on tracking the structural evolution processes of electrocatalysts, recording the reaction intermediates during electrocatalysis, and building a link between the structure and activity/stability of electrocatalysts. Moreover, theoretical considerations are also discussed to assist operando characterization understanding. Finally, some perspectives are provided which are expected to be helpful to tackle the current challenges in operando monitoring and unraveling the reaction mechanisms of OER electrocatalysts.
• #### Evaluation of Detailed Reaction Models for the Modeling of Double Cellular Structures in Gaseous Nitromethane Detonation

(American Institute of Aeronautics and Astronautics, 2022-01-03) [Conference Paper]
• #### Flame-controlling continuation method for extinction of counterflow sooting flames with detailed chemistry

(American Institute of Aeronautics and Astronautics, 2022-01-03) [Conference Paper]
The generation of S-curves for the extinction of counterflow sooting flames has been accomplished by implementing a flame-controlling continuation method inclusive of soot model. The code can generate solutions for augmented flamelets databases, including soot scalars, useful for Flamelet Progress Variable (FPV) tabulations for sooting turbulent simulations. Indeed, the inclusion of all S-curve's branches brings substantial improvements in the reproduction of extinction/re-ignition regimes or flame/acoustic interactions. In this context, developing a reliable tool for S-curve generation, with coupled reproduction of gas-phase and soot characteristics, is of great importance. The algorithm calculates the flamelet states through a 2-point flame-controlling continuation method with control on species mass fractions. Soot calculation is coupled with gas kinetics at every continuation so that flamelet states are inclusive of soot formation effects on precursors' consumption and flame temperature. The flame and soot features can be correctly predicted along the whole curve with smooth transitions between branches. A brief introduction on general S-curve properties is given, using the implementation on hydrogen flames with different oxidizer's inlet temperatures. Besides, soot characteristics are thoroughly investigated on ethylene flames at different pressures.
• #### Flame-controlling continuation method for extinction of counterflow sooting flames with detailed chemistry

(American Institute of Aeronautics and Astronautics, 2022-01-03) [Conference Paper]
The generation of S-curves for the extinction of counterflow sooting flames has been accomplished by implementing a flame-controlling continuation method inclusive of soot model. The code can generate solutions for augmented flamelets databases, including soot scalars, useful for Flamelet Progress Variable (FPV) tabulations for sooting turbulent simulations. Indeed, the inclusion of all S-curve's branches brings substantial improvements in the reproduction of extinction/re-ignition regimes or flame/acoustic interactions. In this context, developing a reliable tool for S-curve generation, with coupled reproduction of gas-phase and soot characteristics, is of great importance. The algorithm calculates the flamelet states through a 2-point flame-controlling continuation method with control on species mass fractions. Soot calculation is coupled with gas kinetics at every continuation so that flamelet states are inclusive of soot formation effects on precursors' consumption and flame temperature. The flame and soot features can be correctly predicted along the whole curve with smooth transitions between branches. A brief introduction on general S-curve properties is given, using the implementation on hydrogen flames with different oxidizer's inlet temperatures. Besides, soot characteristics are thoroughly investigated on ethylene flames at different pressures.
• #### Large eddy simulation of multi-regime burner: a reaction mechanism sensitivity analysis

(American Institute of Aeronautics and Astronautics, 2022-01-03) [Conference Paper]
High Reynolds number jets and mixture inhomogeneities enhance the presence of local reaction zones at different combustion regimes. From a modeling perspective, the multi-regime process requires ad-hoc models to be accurately described. In this work, highly resolved large eddy simulations of the Darmstadt multi-regime burner, which spans regimes from a fully non-premixed flame in the core jet region to an outer premixed flame as well as local extinction and re-ignition, are conducted using the eddy dissipation concept. Three different reaction mechanisms for methane are considered to study the effects of the kinetics model on the solution, including the detailed GRI Mech 3.0 and two reduced ones. The averages and fluctuations of the main scalars are compared against experimental data, and the mixing lines and conditional averages in the mixture fraction-progress variable space are also contrasted. The results highlight that a detailed description of chemical kinetics leads to a shrinkage of the predicted non-premixed flame and improves the prediction of the carbon monoxide mass fraction, when compared to the predictions obtained with the reduced chemistry models.
• #### Uncertainty Quantification and Sensitivity Analysis for In-plane Thermo-mechanical Properties of 3-D Textile Composites

(American Institute of Aeronautics and Astronautics, 2022-01-03) [Conference Paper]
In this paper, uncertainty quantification and sensitivity analysis are performed for investigating the equivalent in-plane thermo-mechanical properties of 3-D orthogonal interlock composites. The composite properties are calculated based on the asymptotic expansion homogenization method omitting out-of-plane periodicity. The analysis herein employs 17 independent properties of constituents as inputs whereby six homogenized properties of composites become the quantity of interests (QOIs). Polynomial chaos expansion (PCE) is used to quantify the output uncertainty and the variance-based sensitivity indices. Two cases are investigated to understand the effects of material variation of constituents on each output of interest. The results show that the PCE model is highly accurate in quantifying the statistical outputs. Furthermore, acceptable accuracy for all QOIs is obtained by 100 sampling points. It is also found that material selection of constituents will determine the importance of input parameters in the calculation of QOIs.
• #### Effect of O2/CO2ratio on stability and near field structure of oxyfuel jet diffusion flames at atmospheric pressure.

(American Institute of Aeronautics and Astronautics, 2022-01-03) [Conference Paper]
This paper presents an experimental study on the stability and structure of non-premixed CO2 diluted oxyfuel jet flames. DSLR imaging and OH Planar Laser-Induced Fluorescence (PLIF) were used to investigate the nearfield structure of a series of methane jet flames. Three oxidizer compositions (O2/CO2 ratios of 50/50, 40/60, and 32/68) were considered for a fixed co-flow velocity of 0.35 m/s. The PLIF Images were post-processed using MATLAB to obtain OH layer thickness, flame attachment height, and radius. Results show that increasing the CO2 level in the co-flow leads to a reduction in the OH layer thickness and sooting propensity. Both attachment radius and height were found to increase with increased CO2 content in the oxidizer. Furthermore, it was also observed that the flame attachment radius decreased as jet velocity increased while the flame attachment height tended to increase with higher jet velocity.
• #### Knock propensity in a thermally inhomogeneous DME/air mixture: a DNS study

(American Institute of Aeronautics and Astronautics, 2022-01-03) [Conference Paper]
Superknock propensity in a stoichiometric dimethyl-ether (DME)/air mixture with temperature inhomogeneities under realistic IC engine conditions is investigated using two-dimensional direct numerical simulations (DNS). The developing detonation regime at different conditions is identified by varying the initial mean temperature lying in the low-, intermediate-, and high-temperature chemistry regimes, the level of temperature fluctuations, and its characteristic length scale. We found that the cool flame from the first-stage ignition induces synergistic effects on promoting knock tendency. First, it significantly decreases a minimum run-up distance requirement for developing detonation due to the low-temperature chemistry. Second, analyzing the temporal evolution of the spatial distribution of the ignition delay field reveals that the heat release rate from the first-stage ignition effectively modifies the initial field of the ignition delay time, thereby shifting the mixture towards the developing detonation regime. The interaction of multiple ignition kernels is also found to play an important role in enhancing the onset of detonation.
• #### Emerging Era of Electrolyte Solvation Structure and Interfacial Model in Batteries

(ACS Energy Letters, American Chemical Society (ACS), 2022-01-02) [Article]
Over the past two decades, the solid–electrolyte interphase (SEI) layer that forms on an electrode’s surface has been believed to be pivotal for stabilizing the electrode’s performance in lithium-ion batteries (LIBs). However, more and more researchers currently are realizing that the metal-ion solvation structure (e.g., Li+) in electrolytes and the derived interfacial model (i.e., the desolvation process) can affect the electrode’s performance significantly. Thus, herein we summarize recent research focused on how to discover the importance of an electrolyte’s solvation structure, develop a quantitative model to describe the solvation structure, construct an interfacial model to understand the electrode’s performance, and apply these theories to the design of electrolytes. We provide a timely review on the scientific relationship between the molecular interactions of metal ions, anions, and solvents in the interfacial model and the electrode’s performance, of which the viewpoint differs from the SEI interpretations before. These discoveries may herald a new, post-SEI era due to their significance for guiding the design of LIBs and their performance improvement, as well as developing other metal-ion batteries and beyond.
• #### A decoupled modeling approach and experimental measurements for pyrolysis of C6-C10 saturated fatty acid methyl esters (FAMEs)

(Combustion and Flame, Elsevier BV, 2022-01) [Article]
Biodiesels are promising renewable fuels that can aid in the transition to carbon neutrality. The high molecular weight and complex composition of real biodiesel fuels complicate development of compact kinetic models needed for engine simulations. Our group previously proposed the functional group approach (FGMech) to model real-fuel combustion based on the identification of intrinsic relationships between fuel molecular structure and model parameters. Establishing these relationships requires a database consisting of the model parameters of pure fuels for training. In this work, we selected five fatty acid methyl esters (FAMEs) as target fuels, including methyl pentanoate (MPE), methyl hexanoate (MHX), methyl heptanoate (MHP), methyl octanoate (MO) and methyl nonanoate (MN). To facilitate development of an FGMech reaction scheme, a decoupling model approach is adopted here for model construction. Lumped reaction mechanisms are developed to describe the (oxidative) pyrolysis of fuels while a detailed model is used for describing the conversion of pyrolysis intermediates. To validate the present model, pyrolysis experiments for these FAMEs are conducted in a jet-stirred reactor (JSR) at 1 atm and over 790–1120 K. Both the synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and gas chromatography (GC)/GC–MS are applied for measuring pyrolysis intermediates. The fuels, primary hydrocarbon and oxygenated products, secondary products including various aromatic compounds, are identified and quantified for model validation. The present model well-predicts the temperature window of fuel decomposition, and reasonably predicts the yields of most pyrolysis products under both present atmospheric conditions and high pressure conditions in literature. The agreement between the measured and predicted results indicates that the present decoupling methodology can accurately describe fuel decomposition and the evolution of intermediates under pyrolysis conditions. In addition, it is found that increasing alkyl CH2 groups in C6 to C10 FAMEs has little influence on the yields of primary oxygenated products; however, increasing yields of hydrocarbon products with increasing alkyl CH2 groups indicates that alkane chemistry becomes more important moving from MPE to MN.
• #### On the effects of CO2 atmosphere in the pyrolysis of Salicornia bigelovii

(Bioresource Technology Reports, Elsevier BV, 2022-01) [Article]
This study focuses on understanding the effects of a CO$_2$ atmosphere on the pyrolysis of $\textit{Salicornia bigelovii}$ by performing a detailed kinetic analysis and investigating the pyrolysis products. In comparison to N$_2$ pyrolysis, CO$_2$ pyrolysis increased the amounts of acids, phenols, amines/amides and N-aromatics in the bio-oil. Biochar showed a 6.5% increase in carbon and a 5.8% decrease in oxygen due to the presence of CO$_2$ in the pyrolysis atmosphere. CO$_2$ also inhibited the volatilization of certain functional groups, such as phenols, tertiary alcohols and aromatics from the biochar, and the surface area of the biochar was 12 times larger than pyrolysis in N$_2$ atmosphere. Pyrolysis in CO$_2$ led to an increase in the average apparent activation energy from 146.5 kJ mol$^{−1}$ in N$_2$ to 163.4 kJ mol$^{−1}$. The kinetic equation was found to conform to a three dimensional diffusion mechanism. Finally, the pre-exponential factor was determined for each reaction.
• #### 'All In One' SARS-CoV-2 variant recognition platform: Machine learning-enabled point of care diagnostics

(Biosensors and Bioelectronics: X, Elsevier BV, 2022-01) [Article]
Point of care (PoC) devices are highly demanding to control current pandemic, originated from severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2). Though nucleic acid-based methods such as RT-PCR are widely available, they require sample preparation and long processing time. PoC diagnostic devices provide relatively faster and stable results. However they require further investigation to provide high accuracy and be adaptable for the new variants. In this study, laser-scribed graphene (LSG) sensors are coupled with gold nanoparticles (AuNPs) as stable promising biosensing platforms. Angiotensin Converting Enzyme 2 (ACE2), an enzymatic receptor, is chosen to be the biorecognition unit due to its high binding affinity towards spike proteins as a key-lock model. The sensor was integrated to a homemade and portable potentistat device, wirelessly connected to a smartphone having a customized application for easy operation. LODs of 5.14 and 2.09 ng/mL was achieved for S1 and S2 protein in the linear range of 1.0–200 ng/mL, respectively. Clinical study has been conducted with nasopharyngeal swabs from 63 patients having alpha (B.1.1.7), beta (B.1.351), delta (B.1.617.2) variants, patients without mutation and negative patients. A machine learning model was developed with accuracy of 99.37% for the identification of the SARS-Cov-2 variants under 1 min. With the increasing need for rapid and improved disease diagnosis and monitoring, the PoC platform proved its potential for real time monitoring by providing accurate and fast variant identification without any expertise and pre sample preparation, which is exactly what societies need in this time of pandemic.
• #### Selective benzylic Csp3–H bond activations mediated by a phosphorus–nitrogen PN3P-nickel complex

(Chemical Communications, Royal Society of Chemistry (RSC), 2022) [Article]
In contrast to the typical Csp2−H activation, a PN3P-Nickel complex chemoselectively cleaved the benzylic Csp3–H bond of toluene in the presence of KHMDS, presumably via an in situ generated potassium benzyl intermediate. Under similar conditions, CO underwent deoxygenation to afford the corresponding nickel cyano complex, and ethylbenzene was dehydrogenated to give styrene and a nickel hydride compound. 2,6-xylyl isocyanide was transformed into an unprecedented indolyl complex, likely by trapping the activated benzyl species with a isocyanide moiety.