Conversion Applications Research Articles

Improvement in electrocatalytic behavior of hydrothermally prepared SrBi2O4 with g-CN toward OER activity

The depletion of fossil fuel reservoirs has led to a serious concern related to the energy industry, with by-products generated from their combustion harming the environment. Hence, it is crucial to find an alternative to fossil fuels that has large reserves. The spinel is an efficient class that can provide reliable source of fuel by coupling with graphitic carbon nitride (g-CN). Herein, we hydrothermally developed the non-transition metal-based spinel with g-CN composite for oxygen evolution reaction (OER) activity. The resulting samples were thoroughly characterized using various analytical techniques. All characterizations verify the phase structure of the SrBi2O4/g-CN composite. The nitrogen (N2) adsorption-desorption isotherm indicated a mesoporous structure based on the adsorption isotherm. In addition, the integration of unique-shaped nanoparticles decorated on graphitized carbon nitride nanosheets helps in reducing initial potentials for the OER procedure. Due to their unique mesoporous configuration, SrBi2O4/g-CN catalysts illustrate remarkable electrical conductivity and electrocatalytic activity. The SrBi2O4/g-CN composite exhibited less overpotential (η) of 193 mV at current density (Cd) of 10 mA/cm2 compared to SrBi2O4. The SrBi2O4/g-CN composite revealed remarkable durability and lesser Tafel value of 33 mV/dec. All of the outstanding results obtained from the electrochemical activity suggest as potential electrocatalyst and it can be employed in future energy conversion and water related applications.

A novel FVF-based GHz-range biquad in a 28 nm CMOS FD-SOI technology

Inductor-less CMOS filters with bandwidth exceeding several GHz are required in high-speed data converter applications. This paper introduces two complementary biquad filters, one N-based and the other P-based, utilizing the well-established flipped voltage follower (FVF) stage. These filters exhibit more than 7 GHz cut-off frequency and a low power consumption of 0.54 mW/pole for the N-type biquad, and 0.3 mW/pole for the P-type one, demonstrating impressive figures-of-merit (FOMs) even considering bandwidth and dynamic range. The implementation of these biquads in the STMicroelectronics FD-SOI 28-nm CMOS process, along with extensive simulations, ensures stable performance under process, supply voltage and temperature (PVT) variations and mismatches, as confirmed by post-layout simulations. Notably, the area occupied by each biquad is merely 246 μm2 for N-type biquad and 193 μm2 for P-type, marking one of the smallest footprints in the existing literature. The achieved figures-of-merit are noteworthy, showcasing excellent power efficiency, minimal area occupation, and commendable dynamic range.

Computational Argumentation-based Chatbots: A Survey

Chatbots are conversational software applications designed to interact dialectically with users for a plethora of different purposes. Surprisingly, these colloquial agents have only recently been coupled with computational models of arguments (i.e. computational argumentation), whose aim is to formalise, in a machine-readable format, the ordinary exchange of information that characterises human communications. Chatbots may employ argumentation with different degrees and in a variety of manners. The present survey sifts through the literature to review papers concerning this kind of argumentation-based bot, drawing conclusions about the benefits and drawbacks that this approach entails in comparison with standard chatbots, while also envisaging possible future development and integration with the Transformer-based architecture and state-of-the-art Large Language models.

Hot carriers from intra- and interband transitions in gold-silver alloy nanoparticles

Hot electrons and holes generated from the decay of localised surface plasmons in metallic nanoparticles can be harnessed for applications in solar energy conversion and sensing. In this paper, we study the generation of hot carriers in large spherical gold-silver alloy nanoparticles using a recently developed atomistic modelling approach that combines a solution of Maxwell’s equations with large-scale tight-binding simulations. We find that hot-carrier properties depend sensitively on the alloy composition. Specifically, nanoparticles with a large gold fraction produce hot carriers under visible light illumination while nanoparticles with a large silver fraction require higher photon energies to produce hot carriers. Moreover, most hot carriers in nanoparticles with a large gold fraction originate from interband transitions which give rise to energetic holes and ‘cold’ electrons near the Fermi level. Increasing the silver fraction enhances the generation rate of hot carriers from intraband transitions which produce energetic electrons and ‘cold’ holes. These findings demonstrate that alloy composition is a powerful tuning parameter for the design of nanoparticles for applications in solar energy conversion and sensing that require precise control of hot-carrier properties.

Enhancing terahertz magneto-optical effects in wafer-scale RIG single crystal thick films with anti-reflective coatings for improved transmittance

Wafer-scale rare-earth iron garnet (RIG) single crystal thick films were fabricated on 3-in. gadolinium gallium garnet (GGG) substrates using liquid phase epitaxy. The terahertz transmittance of the RIG crystals improved after removing the GGG substrate by polishing. The time-domain spectra at Terahertz (THz) frequencies indicate the existence of a magneto-optical effect in RIG samples. The results indicate that the RIG samples exhibit a high refractive index of ∼4.50 within the 0.1–1.0 THz frequency range, a transmittance of around 40%, and an absorption rate of only 10–50 cm−1. The Faraday rotation angles of the thick single-crystal films of the RIG samples were measured using a THz-TDS system. The RIG has a thickness of ∼330 μm. The Faraday rotation angles of RIG crystals at THz frequencies can reach up to 16° when an external magnetic field of 0.18 T is applied. The Verdet constants of the RIG sample were calculated to be ∼120°/mm/T. To improve the transmittance of the RIG sample, epoxy resin and polymethylpentene (TPX) were used as anti-reflective films. The transmittance of the RIG sample increased by ∼5% for the 80 μm thick epoxy and about 10% for the 320 μm thick TPX. Therefore, this RIG single crystal thick film can achieve a low loss, a high transmittance, and a strong magneto-optical effect in the terahertz region with the cooperation of a reflection-reducing film. It is expected to have wide applications in terahertz magnetic polarization conversion, non-reciprocal phase shifters, and isolators.

Experimental study on liquid piston Stirling engine combined with self-rectifying turbine.

A liquid piston Stirling engine is an external combustion engine that uses air and water under atmospheric pressure as its working fluids. Resulting from its uncomplicated design and the capacity to operate under relatively low temperature differentials of less than 100 °C, it has attracted considerable attention in recent years. This paper presents the fundamental characteristics of the liquid piston engine combined with a self-rectifying turbine for the advancement of thermal generators. When the turbine is installed in the water region rather than in the air region, it exhibits unidirectional rotation with a rotational speed directly proportional to the velocity amplitude of the reciprocating axial flow. Additionally, the acoustic impedance within the duct section containing the turbine is determined, demonstrating that the real part of impedance rises with increasing axial velocity, indicating a loss mechanism similar to the minor loss. Furthermore, the installation of the turbine results in a breakdown of symmetry in the engine oscillation mode. To maintain symmetry and improve system design, future developments must consider the installation of a turbine in each unit. These findings can pave the way to the design of liquid piston Stirling engines and their applications in thermal energy conversion.

Thermal conductivity of double polymorph Ga2O3 structures

Recently discovered double gamma/beta (γ/β) polymorph Ga2O3 structures constitute a class of novel materials providing an option to modulate functional properties across interfaces without changing the chemical compositions of materials, in contrast to that in conventional heterostructures. In this work, for the first time, we investigate thermal transport in such homo-interface structures as an example of their physical properties. In particular, the cross-plane thermal conductivity (k) was measured by femtosecond laser-based time-domain thermoreflectance with MHz modulation rates, effectively obtaining depth profiles of the thermal conductivity across the γ-/β-Ga2O3 structures. In this way, the thermal conductivity of γ-Ga2O3 ranging from 1.84 to 2.11 W m−1 K−1 was found to be independent of the initial β-substrates orientations, in accordance with the cubic spinel structure of the γ-phase and consistently with the molecular dynamics simulation data. In turn, the thermal conductivity of monoclinic β-Ga2O3 showed a distinct anisotropy, with values ranging from 10 W m−1 K−1 for [−201] to 20 Wm−1 K−1 for [010] orientations. Thus, for double γ-/β-Ga2O3 polymorph structures formed on [010] β-substrates, there is an order of magnitude difference in thermal conductivity across the γ/β interface, which can potentially be exploited in thermal energy conversion applications.

Single-walled Carbon Nanotubes Wrapped with Charged Polysaccharides Enhance Extracellular Electron Transfer.

Microbial electrochemical systems (MESs) rely on the microbes' ability to transfer charges from their anaerobic respiratory processes to electrodes through extracellular electron transfer (EET). To increase the generally low output signal in devices, advanced bioelectrical interfaces tend to augment this problem by attaching conducting nanoparticles, such as positively charged multiwalled carbon nanotubes (CNTs), to the base carbon electrode to electrostatically attract the negatively charged bacterial cell membrane. On the other hand, some reports point to the importance of the magnitude of the surface charge of functionalized single-walled CNTs (SWCNTs) as well as the size of functional groups for interaction with the cell membrane, rather than their polarity. To shed light on these phenomena, in this study, we prepared and characterized well-solubilized aqueous dispersions of SWCNTs functionalized by either positively or negatively charged cellulose-derivative polymers, as well as with positively charged or neutral small molecular surfactants, and tested the electrochemical performance of Shewanella oneidensis MR-1 in MESs in the presence of these functionalized SWCNTs. By simple injection into the MESs, the positively charged polymeric SWCNTs attached to the base carbon felt (CF) electrode, and as fluorescence microscopy revealed, allowed bacteria to attach to these structures. As a result, EET currents continuously increased over several days of monitoring, without bacterial growth in the electrolyte. Negatively charged polymeric SWCNTs also resulted in continuously increasing EET currents and a large number of bacteria on CF, although SWCNTs did not attach to CF. In contrast, SWCNTs functionalized by small-sized surfactants led to a decrease in both currents and the amount of bacteria in the solution, presumably due to the detachment of surfactants from SWCNTs and their detrimental interaction with cells. We expect our results will help researchers in designing materials for smart bioelectrical interfaces for low-scale microbial energy harvesting, sensing, and energy conversion applications.

Improving light harvesting and charge carrier separation enabling enhanced photoelectrochemical hydrogen production by Sb2S3-decorated TiO2 nanotube arrays on porous Ti-photoanodes

The Ag + ions doped TiO2 nanotube arrays fabricated on Ti mesh through an electrochemical anodization process, and n/n heterostructure formed by coating the TiO2 nanotube array photoanode with an n-type stibnite (Sb2S3) layer improve photoelectrochemical water splitting reaction by enhancing light harvesting and charge carrier separation. Sb2S3 is chosen because of its suitable band gap position and strong visible light response. The Ag + ion incorporated TiO2 nanotube array coated with Sb2S3 exhibits a photocurrent density of 6.5 mA cm−2 vs. RHE, whereas bare TiO2 nanotube array coated with Sb2S3 and pristine TiO2 nanotube array exhibit photocurrent densities of 3.6 and 0.27 mA cm−2, respectively, under the same conditions, which is nearly 1.8 and 24 times greater than the TiO2 nanotube array coated with Sb2S3 and pristine TiO2 nanotube array photoanodes. The applied bias photon-to-current efficiency of Ag + ion incorporated TiO2 nanotube array coated with Sb2S3 is 3.6% and the improved Photoelectrochemical performance of Ag + ion doped TiO2 nanotube array coated with Sb2S3 is attributable to higher conductivity of TiO2 nanotube array caused by increased oxygen vacancies and broad optical activity of Sb2S3. The 1-dimensional TiO2 nanotube array device structure in the Ti mesh improves charge separation and light harvesting while reducing photogenerated charge carrier recombination and the potential of this novel device structure for advanced energy conversion applications is highlighted in this study.

Sandwiched heterostructure of NiFe2O4/TiO2 nanocrystals and MXene nanosheets for highly active oxygen electrocatalyst in rechargeable zinc-air batteries

Recent advancements in zinc-air batteries (ZABs) emphasize the need for efficient and sustainable oxygen electrocatalysts. Central to these efforts are metal-organic frameworks (MOFs), renowned for their bifunctional oxygen electrocatalytic capabilities. However, MOFs and their derivatives often exhibit subpar electrical conductivity and stability. Addressing this, we introduce an innovative approach involving MOFs-derived NiFe2O4/TiO2 nanocrystals sandwiched between 2D MXene nanosheets. This hybrid structure, NiFe2O4/TiO2@NC/Ti3C2, successfully enhances conductivity and active site accessibility, thereby enhancing oxygen reduction (ORR) and evolution (OER) reactions. The NiFe2O4/TiO2@Ti3C2–2 hybrid demonstrates excellent bifunctional activity, characterized by a notable ORR's half-wave potential of 0.846 V and an OER's onset potential of 1.5 V with a potential gap (ΔE) of 0.75 V. When employed in a ZAB, the battery achieves a peak power density of 164 mW cm−2 and maintains cycling stability for over 500 h at 10 mA cm−2. Beyond serving as conductive scaffolds, Ti3C2 MXene nanosheets have a vital role in preserving surface areas of the NiFe2O4/TiO2@NC materials. This study not only highlights a successful strategy for improving oxygen reactions in ZABs but also opens up new opportunities for the development of advanced MOF@MXene catalysts in energy conversion applications.

Alkali cation stabilization of defects in 2D MXenes at ambient and elevated temperatures

Transition metal carbides have been adopted in energy storage, conversion, and extreme environment applications. Advancements in their 2D counterparts, known as MXenes, enable the design of unique structures at the ~1 nm thickness scale. Alkali cations have been essential in MXenes manufacturing processing, storage, and applications, however, exact interactions of these cations with MXenes are not fully understood. In this study, using Ti3C2Tx, Mo2TiC2Tx, and Mo2Ti2C3Tx MXenes, we present how transition metal vacancy sites are occupied by alkali cations, and their effect on MXene structure stabilization to control MXene’s phase transition. We examine this behavior using in situ high-temperature x-ray diffraction and scanning transmission electron microscopy, ex situ techniques such as atomic-layer resolution secondary ion mass spectrometry, and density functional theory simulations. In MXenes, this represents an advance in fundamentals of cation interactions on their 2D basal planes for MXenes stabilization and applications. Broadly, this study demonstrates a potential new tool for ideal phase-property relationships of ceramics at the atomic scale.

Beyond Cation Disorder: Site Symmetry‐Tuned Optoelectronic Properties of the Ternary Nitride Photoabsorber ZrTaN3

AbstractTernary nitrides are rapidly emerging as promising compounds for optoelectronic and energy conversion applications, yet comparatively little of this vast composition space has been explored. Furthermore, the crystal structures of these compounds can exhibit a significant amount of disorder, the consequences of which are not yet well understood. Here, the deposition of bixbyite‐type ZrTaN3 thin films is demonstrated by reactive magnetron co‐sputtering and observed semiconducting character, with a strong optical absorption onset at 1.8 eV and significant photoactivity, with prospective application as functional photoanodes. It is found that Wyckoff‐site occupancy of cations is a critical factor in determining these beneficial optoelectronic properties. First‐principles calculations show that cation disorder leads to minor deviations in the total energy but modulates the bandgap by 0.5 eV, changing orbital hybridization of valence and conduction band states. In addition to demonstrating that ZrTaN3 is a promising visible light‐absorbing semiconductor and active photoanode material, the findings provide important insights regarding the role of cation ordering on the electronic structure of ternary semiconductors. In particular, it is shown that not only cation order, but also the cationic Wyckoff site occupancy has a substantial impact on key optoelectronic properties, which can guide future design and synthesis of advanced semiconductors.

Insights on Using Solid Bitumen Reflectance as a Thermal Maturity Proxy in the Bakken Formation, Williston Basin, USA.

To further refine the use of solid bitumen reflectance (BRo in %) as a measurement of thermal maturity in source-rock reservoirs, we examined its relationship to other thermal proxies in the Bakken Formation. Comparisons included criteria from programmed temperature pyrolysis, gas chromatography (GC), and Fourier transform infrared (FTIR) spectroscopy. Thirty-two organic-rich samples from the lower and upper shale members of the Devonian-Lower Carboniferous Bakken Formation were collected from eight cores across the Williston Basin, USA, at depths (∼7575-11,330 ft) representing immature through post peak oil/early condensate thermal maturity conditions based on proximity to current hydrocarbon production. Unmodified BRo values were correlated to programmed temperature pyrolysis parameters (hydrogen index, production index, and T max), normal hydrocarbon and isoprenoid analysis of extractable organic matter (pristane/n-C17 and phytane/n-C18) from GC analysis, and peak ratios from FTIR spectroscopy (branching ratio and A-factor). Strong correlations between unmodified BRo values (not corrected to a vitrinite reflectance equivalent, VRe) and other thermal proxies suggest that BRo can be used as a direct thermal proxy in marine Paleozoic source-rock reservoirs where vitrinite is rare or absent. Moreover, an apparent overestimation of VRe at the lowest thermal maturity investigated herein may argue against the application of BRo conversion to VRe in the Bakken Formation. Solvent extraction caused a consistent decrease in BRo when average post-extraction values from a given well were compared to BRo prior to extraction, although the decrease in mean value was not statistically significant. These results are discussed in the context of advocating for the use of unmodified BRo values as a best practice for thermal maturity determination in Paleozoic marine source-rock reservoirs.

Molybdate-based Nanocrystalline Materials for Efficient Environmental Remediation and Electrochemical Energy Conversion Applications: An Update

Molybdate-based Nanocrystalline Materials for Efficient Environmental Remediation and Electrochemical Energy Conversion Applications: An Update

Minimal doping approach to activate lattice oxygen participation in K2WO4 electrocatalysts for oxygen evolution reaction

Understanding oxygen redox processes is pivotal for advancing oxygen evolution catalysts, critical in electrochemical devices for renewable fuel synthesis. Thermodynamic instability of high entropy metal oxides can interfere with oxygen redox reactions via electrochemical reconstruction. Transforming a W5N4 pre-catalyst into thermodynamically stable K2WO4 through electrochemical treatment in KOH, and incorporating minimal Fe doping, modifies the oxygen evolution reaction (OER) pathway towards oxygen redox activity, significantly influenced by the pH of the electrolyte. The Fe-doped K2WO4 catalyst demonstrates superior OER performance, achieving 10 mA/cm^2 at an overpotential of merely 181 mV (without iR compensation) and sustaining a lifetime of 1200 h at 1000 mA/cm2. Electrochemical methods and DFT calculations confirmed Fe doping creates oxygen vacancies and increases electron density near the Fermi level, enhancing the OER pathway. This methodology offers a versatile approach to adapt high entropy catalysts for broad electrochemical energy conversion applications, highlighting its potential for innovation in renewable energy technologies.

Green synthesis of nanostructured 1T/2H-MoS2 hybrid phase with polyol solvents and microwave heating

Green synthesis approaches have attracted greatly of attention in recent years since they address the issues associated with sustainability than conventional synthesis methods. New research fields in green nanoscience are being developed as a result of the incorporation of green chemistry principles into nanoscience. In this paper, the successful microwave-assisted green synthesis of MoS2 nanoparticles in a single pot using polyol solvents such as ethylene glycol and glycerol is demonstrated. The coexistence of 1T and 2H phases in MoS2 nanomaterials was determined using advanced techniques such as XRD, Raman, XPS, and TEM images. The highest 1T proportion obtained was 84.5% when compared to the 2H phase. The reaction mechanism and the phase transition between 1T and 2H were described and illustrated. The role of polyol solvents in the practical synthesis of nano MoS2 under microwave heating is also evaluated and explained. Due to the ability of the metallic 1T phase to enhance electrical conductivity, it is believed that hybrid nanostructures exhibit superior electrochemical performance for energy storage and conversion applications.

Study on preparation and performance of TiN modified vertically aligned carbon fiber evaporator

The application of solar photothermal conversion is currently one of the main ways to utilize solar energy, therefore it is crucial to find effective materials for photothermal conversion. In this study, carbon fiber evaporators (C-EVAP and R-EVAP) with vertically aligned carbon fiber structure were prepared from ramie and cotton using fiber bundling and carbonization, and then TiN-C-EVAP and TiN-R-EVAP were further obtained by modifying with TiN. The effects of precursor materials and TiN modification on the performance of the evaporators were discussed. The vertically aligned carbon fiber structure facilitates rapid moisture transport similar to the tree stem, enhances the internal reflection of light and improves light absorption. Compared to the short carbon fibers of cotton evaporators, ramie evaporators (R-EVAP and TiN-R-EVAP) with the long vertically aligned carbon fibers and multi-stage hollow structure have better photothermal conversion efficiency. Owing to the wide plasma resonance absorption spectrum and high absorbance of TiN, the TiN modification improves photothermal conversion efficiency of the carbon evaporators. The combination of long vertically aligned carbon fiber structure and TiN modification gives the ramie evaporator efficient photothermal conversion performance. The prepared TiN-R-EVAP has the best photothermal conversion efficiency with an evaporation rate of 1.96 kg·m−2h−1 and an evaporation efficiency of 91.29 % under 1 sunlight. It also has seawater desalination capability and excellent cycling stability, and the typical ion content of the TiN-R-EVAP desalinated condensate can meet the World Health Organization (WHO) standard for usable freshwater salinity. The vertically aligned ramie evaporators similar to the tree stem can be applied to the fields of photothermal conversion and seawater desalination.

Hot Electrons in a Steady State: Interband vs Intraband Excitation of Plasmonic Gold.

Understanding the dynamics of "hot", highly energetic electrons resulting from nonradiative plasmon decay is crucial for optimizing applications in photocatalysis and energy conversion. This study presents an analysis of electron kinetics within plasmonic metals, focusing on the steady-state behavior during continuous-wave (CW) illumination. Using an inelastic spectroscopy technique, we quantify the temperature and lifetimes of distinct carrier populations during excitation. A significant finding is the monotonic increase in hot electron lifetime with decreases in electronic temperature. We also observe a 1.22× increase in hot electron temperature during intraband excitation compared to interband excitation and a corresponding 2.34× increase in carrier lifetime. The shorter lifetimes during interband excitation are hypothesized to result from direct recombination of nonthermal holes and hot electrons, highlighting steady-state kinetics. Our results help bridge the knowledge gap between ultrafast and steady-state spectroscopies, offering critical insights for optimizing plasmonic applications.

Joint sparse optimization: lower-order regularization method and application in cell fate conversion

Multiple measurement signals are commonly collected in practical applications, and joint sparse optimization adopts the synchronous effect within multiple measurement signals to improve model analysis and sparse recovery capability. In this paper, we investigate the joint sparse optimization problem via ℓp,q regularization ( 0⩽q⩽1⩽p ) in three aspects: theory, algorithm and application. In the theoretical aspect, we introduce a weak notion of joint restricted Frobenius norm condition associated with the ℓp,q regularization, and apply it to establish an oracle property and a recovery bound for the ℓp,q regularization of joint sparse optimization problem. In the algorithmic aspect, we apply the well-known proximal gradient algorithm to solve the ℓp,q regularization problems, provide analytical formulas for proximal subproblems of certain specific ℓp,q regularizations, and establish the global convergence and linear convergence rate of the proximal gradient algorithm under some mild conditions. More importantly, we propose two types of proximal gradient algorithms with the truncation technique and the continuation technique, respectively, and establish their convergence to the ground true joint sparse solution within a tolerance relevant to the noise level and the recovery bound under the assumption of restricted isometry property. In the aspect of application, we develop a novel method, based on joint sparse optimization with lower-order regularization and proximal gradient algorithm, to infer the master transcription factors for cell fate conversion, which is a powerful tool in developmental biology and regenerative medicine. Numerical results indicate that the novel method facilitates fast identification of master transcription factors, give raise to the possibility of higher successful conversion rate and in the hope of reducing biological experimental cost.

Metal-organic frameworks Derived NiFe-hydroxides for efficient Electrocatalytic hydrogen evolution

Ni-based layered double hydroxides (Ni-LDH) is regarded as one of the most promising electrocatalyst for hydrogen evolution reaction (HER). To further improve the HER performance of Ni-LDH, it is important to provide more active sites and decrease reaction energy. Herein, bimetal NiFe-LDH derived from NiFe-MIL was constructed by two-steps hydrothermal strategy. NiFe-LDH-0.3 displays the excellent HER activity, which achieves a low overpotential of 148 mV at 10 mA·cm-2. This work offers a novel strategy to design and develop highly efficient electrocatalyst via for HER activity and other energy conversion application.