Rational synthesis of ternary PtIrNi nanocrystals with enhanced poisoning tolerance for electrochemical ethanol oxidation

The development of highly efficient and durable anode materials for ethanol electro-oxidation remains a challenge. Herein, we report the synthesis of Pt1−x−yIrxNiy nanocrystals via one-step procedure by ultrasonic-assisted co-reduction of the metal precursors using ascorbic acid as a mild reducing agent and pluronic F127 as a structure directing agent. The catalytic performance of this ternary catalyst towards electrochemical oxidation of ethanol was examined and compared to its mono and binary Pt counterparts (Pt, Pt1−xIrx, and Pt1−yNiy) that are synthesized by the same method. TEM analysis showed a porous nanodendritic structure for the synthesized ternary electrocatalyst with an average size of 20 ± 1 nm. The electrochemical measurements revealed an electrochemically active surface area, ECSA, of 73 m2 g−1. The as-synthesized ternary electrocatalyst showed an improved catalytic activity towards ethanol oxidation in 1 M KOH with a measured mass activity of 3.8 A mg−1 which is 1.7, 2.0, and 3.2 times higher than that of Pt1−xIrx, Pt1−yNiy, and Pt, respectively. Additionally, the Pt1−x−yIrxNiy nanocrystals expressed high poisoning tolerance (jf/jb = 4.5) and high durability compared to its mono and binary counterparts.Scopu

Influence of Sinusoidal Drive Speed Modulation on Rotor with Continuous Stator Contact

Torsional vibrations experienced by drill strings can be detrimental to drilling operations. With a goal of understanding torsional vibrations experienced by drill strings and determining means to attenuate undesired vibrations, the authors have studied the effect of adding a sinusoidal modulation to a constant rotation speed of a drill string. A combination of modeling, analysis, and experiments is used to explore the influence of this rotation input modulation on the system response. The drill string is modeled as a modified Jeffcott rotor, which is described by a system with three degrees of freedom. Considering the case of forward whirling of a rotor in continuous contact with a stator, the equations of motion are reduced to a single degree-of-freedom nonlinear oscillator describing the torsional motions. In order to understand the fast time scale and slow time scale components of the motion, the method of direct partitions of motions is used to determine an approximate response to the nonlinear oscillator. The obtained results of the analysis illustrate that with the sinusoidal modulation of the rotor drive speed, the equivalent torsion stiffness can be enhanced and the character of the friction force at the contact can be made smooth. The analyses helps bring forth the stabilizing influence of the added sinusoidal input to the rotor drive speed. Over the considered parameter ranges, the numerical results obtained with the full three degree-of-freedom model and the reduced single degree-of-freedom model are found to be in agreement with each other. Furthermore, the results from these models are found to compare well with those obtained by using the method of direct partition of motions. Experiments with a laboratory scale drill-string arrangement are to be carried out to validate the analytical and numerical findings and further explore the effectiveness of the drive speed modulation on the rotor dynamics.qscienc

Synthesis & Performance Evaluation of Hybrid Cathode Materials for Energy Storage

Research into the development of novel cathode materials for energy storage applications is progressing at a rapid rate to meet the ever-growing demands of modern society. Amongst various options, batteries are playing a vital role to replace conventional energy sources such as fossil fuels with green technologies. Among various battery technologies, lithium-ion batteries (LIBs) have been well explored and have succeeded in being adjusted with find many commercial applications. At the same time, as an alternative to LIBs, Sodium-Ion Batteries (SIBs) are also gaining popularity due to the presence of Sodium (Na) in abundance and its similar electrochemical characteristics with lithium (Li). However, SIBs are suffering from many challenges such as slow ionic movement, instability in different phases, and low energy density, etc. Many strategies in the literature have been proposed to address the aforementioned challenges of SIBs. Among them, the substitution of Na with Li to form hybrid cathode materials has turned out to be quite promising. The present work aims to investigate the effect of Na substitution with Li in a pyrophosphate framework. Towards this direction, Na(2-x) LixFeP2O7 (x=0,0.6) hybrid cathode materials were synthesized, and their structural, thermal, and electrochemical properties were studied. It is noticed that the incorporation of Li in the triclinic structure of Na2FeP2O7 has a significant effect on its thermal and electrochemical performance. This study can be considered as a baseline to develop some other pyrophosphate-based high-performance hybrid cathode materials

Synthesis and performance evaluation of Na(2-x)LixFeP2O7 (x=0, 0.6) hybrid cathodes

This study reports hybrid cathodes formation by cation substitution in which Li+ substitution has been considered for Na+ in the structure of Na(2-x)LixFeP2O7 (x=0, 0.6) to form Na1.4Li0.6FeP2O7 cathodes. Na(2-x)LixFeP2O7 (x=0, 0.6) cathodes were synthesized using the solid-state synthesis technique and characterized by various methods. The structural analysis (XRD, FE-SEM) indicates that the submicron-sized, phase pure, and crystalline materials having irregular morphology have been developed. Moreover, Li+ substitution does not alter the triclinic parent structure of Na2FeP2O7. Thermogravimetric analysis (TGA) shows that Li+ substitution into Na2FeP2O7 improves its thermal stability up to 550 °C with only ∼5 % weight loss. The electrochemical performance of Na2FeP2O7 and Na1.4Li0.6FeP2O7 in both lithium (Li) and sodium (Na) half-cells is investigated using different electrochemical techniques. It is noticed that Na1.4Li0.6FeP2O7 is electrochemically active both in lithium (Li) and sodium (Na) cells with promising cyclability. However, compared with Na2FeP2O7, Na1.4Li0.6FeP2O7 suffers from inferior electrochemical performance, which might be associated with the lattice distortion of Na2FeP2O7 due to Li+ substitution having a lower ionic radius than the Na+. Considering Na2FeP2O7 as a baseline material, a new hybrid Na1.4Li0.6FeP2O7 cathode has been developed, which can be used to synthesize other new cathode materials with improved performance.This publication was made possible by NPRP Grant#NPRP11S-1225-170128 from Qatar National Research Fund (a member of the Qatar Foundation). Statements made herein are solely the responsibility of the authors. Ramazan Kahraman and all the contributors would like to acknowledge the financial support of QU internal grant-QUCG-CENG-20/21-2. FE-SEM analysis was accomplished at the Central Laboratory Unit (CLU), Qatar University, Doha, Qatar.Scopu

Electrochemical Performance of Na3V2(PO4)2F3 Electrode Material in a Symmetric Cell

A NASICON-based Na3V2(PO4)2F3 (NVPF) cathode material is reported herein as a potential symmetric cell electrode material. The symmetric cell was active from 0 to 3.5 V and showed a capacity of 85 mAh/g at 0.1 C. With cycling, the NVPF symmetric cell showed a very long and stable cycle life, having a capacity retention of 61% after 1000 cycles at 1 C. The diffusion coefficient calculated from cyclic voltammetry (CV) and the galvanostatic intermittent titration technique (GITT) was found to be ~10−9–10−11, suggesting a smooth diffusion of Na+ in the NVPF symmetric cell. The electrochemical impedance spectroscopy (EIS) carried out during cycling showed increases in bulk resistance, solid electrolyte interphase (SEI) resistance, and charge transfer resistance with the number of cycles, explaining the origin of capacity fade in the NVPF symmetric cell. Finally, the postmortem analysis of the symmetric cell after 1000 cycles at a 1 C rate indicated that the intercalation/de-intercalation of sodium into/from the host structure occurred without any major structural destabilization in both the cathode and anode. However, there was slight distortion in the cathode structure observed, which resulted in capacity loss of the symmetric cell. The promising electrochemical performance of NVPF in the symmetric cell makes it attractive for developing long-life and cost-effective batteries.Funding: This publication was financially supported by Qatar University through the internal grant-QUCG-CENG-20/21-2. This work was also supported by the Qatar National Research Fund (a member of the Qatar Foundation) through the NPRP Grant#NPRP11S-1225-170128.Scopu

Synthesis and Characterization of Soluble Thiophene-Selenophene- and Tellurophene-Vinylene Copolymers

Organic electronic devices based on polymers received significant attention in the last decade, especially for organic photovoltaics (OPVs) and field-effect transistors (OFETs) despite their performances and stability clearly falling short of today's state-of-the-art crystalline silicon or copper indium germanium selenide (CIGS)-based devices. Flexibility in the manufacturing, light weight, lower fabrication cost, ease of integration into various devices, and large area coating are some of the major potential advantages of polymers over inorganic devices. 1 Among organic polymers, conjugated polymers attracted widespread attention for a wide range of applications. Thiophene-containing conjugated polymers, especially, poly(3-alkylthiophne) (P3AT) has been subjected to intensive research over last decade due to their excellent optical and electronic properties. 2 Moreover, poly(thienylenevinylene) (PTV) class of polymers displays high charge carrier mobilities in OFETs and promising performances in OPVs. 3 When a single solubilizing alkyl chain is included onto the PTV backbone, the resulting copolymer can be solution processed for optical devices. One simple strategy to manipulate the copolymer property is by changing the heteroatom of the thiophene from sulfur to other chalcogens, selenium or tellurium. 4 Theoretical calculations indicated that substitution with selenium or tellurium may reduce the optical band gap of the resulting polymer in comparison to their sulfur-containing analogues. Inclusion of larger and more polarizable selenium or tellurium also expected to have a strong influence on the charge transport properties. Notably, Heeney and co-workers showed that the band gap of P3AT can be reduced by as much as 0.3 eV by only substituting sulfur with selenium in the polymer backbone. 5 The reduction of band gap resulted from larger and more polarizable selenium facilitate better π orbital overlap with the polymer backbone and thus stabilize the polymer LUMO (lowest unoccupied molecular orbital). Low-lying LUMO levels are believe to facilitate both electron injection and transport. Recently, PBDTT-SeDPP polymer showed a high Jsc of 16.8 mA/cm2, a Voc of 0.69 V, and a FF of 62%, enabling the best PCE of 7.2%. 6 However, despite fascinating properties of selenium substituted polymers, tellurium containing polymers are less explored, may be due to challenging tellurium chemistry. Jahnke and co-workers recently reported first soluble tellurophene polymer, poly(3-alkyltellurophene) (P3ATe), prepared by both electrochemical and Kumuda coupling polymerization method. 7 Even though, preliminary PCE (1.1%) was modest, tellurium substitution resulted in red-shifted film absorption. In this contribution, we report the synthesis and characterization of vinylene copolymers containing 3-alkylthiophene, selenophene or tellurophene. This allows us systematically investigate the role of selenium or tellurium on the polymer properties. Here, we report the first synthesis of novel 2,5-dibrominated 3-alkyltellurophene monomer and its Pd[0]-catalyzed copolymerization with (E)1,2-bis(tributylstannyl)ethylene to afford poly(3-alkyltellurophenylenevinylene) (P3ATeV). 8 We compare the optoelectronic properties of P3ATeV with analogous sulfur (P3ATV) and selenium (P3ASV) containing polymers. Preliminary OFET data will also be incorporated. Scheme 1. Structures of P3AX, P3AXV copolymers.Qscienc

Tailoring the deposition of MoSe2 on TiO2 nanorods arrays via radiofrequency magnetron sputtering for enhanced photoelectrochemical water splitting

MoSe2/1 D TiO2 nanorods (NRs) heterojunction assembly was systematically fabricated, and its photoelectrocatalytic properties were investigated. The fabrication process involves the growth of 1D TiO2 NRs arrays on FTO substrates using hydrothermal synthesis followed by the deposition of MoSe2 nanosheets on the TiO2 NRs using radiofrequency magnetron sputtering (RF magnetron sputtering). The photoelectrochemical properties of the heterojunction were explored and optimized as a function of the thickness of the MoSe2 layer, which was controlled by the sputtering time. The MoSe2 grows perpendicularly on TiO2 NRs in a 2D layered structure, maximizing the exposed active edges, an essential aspect that permits maximum exploitation of deposited MoSe2. Compared to pure TiO2 NRs, the heterojunction nanostructured assembly displayed excellent spectral and photoelectrochemical properties, including more surface oxygen vacancies, enhanced visible-light absorption, higher photocurrent response, and decreased charge transfer resistance. In particular, the sample synthesized by sputtering of MoSe2 for 90 s, i.e., MoSe2@TiO2-90 s, depicted the highest current density (1.86 mA cm−2 at 0.5 V vs. Ag/AgCl) compared to other samples. The excellent photoelectrochemical activity of the heterojunction stemmed from the synergy between tailored loading of MoSe2 nanosheets and the 1D structure of TiO2 NRs, which afford a high surface/volume ratio, effective charge separation, fast electron transfer, and easy accessibility to the MoSe2 active edges. These factors boost the catalytic activity.This work was made possible by NPRP Grant no. NPRP 12S-0304-190218 from the Qatar National Research Fund (a member of the Qatar Foundation). The statements made herein are solely the responsibility of the authors. Open Access funding provided by the Qatar National Library.Scopu