Conversion Applications Research Articles

Chiral Au@CeO2 Helical Nanorods with Spatially Separated Structures for Polarization‐dependent N2 Photofixation

Chiral photocatalytic nanomaterials possess numerous unique properties and hold promise for various applications in chemical synthesis, environmental protection, energy conversion, and photoelectric devices. Nevertheless, it is uncommon to develop effective means to enhance the asymmetric catalytic performances of chiral plasmonic nanomaterials. In this study, a type of L/D‐Au@CeO2 helical nanorods (HNRs) was fabricated by selectively growing CeO2 on the surface of Au HNRs via a facile wet‐chemistry construction method. Chiral Au@CeO2 HNRs, featuring Au and CeO2 with spatially separate structures, exhibited the highest photocatalytic performance for N2 fixation, being 50.80 ± 2.64 times greater than Au HNRs. Furthermore, when L‐Au@CeO2 HNRs corresponded left circularly polarized light (CPL) and D‐Au@CeO2 HNRs corresponded right CPL, their photocatalytic efficiency was enhanced by 3.06 ± 0.06 times in contrast with the samples illuminated with the opposite CPL, which can be attributed to the asymmetrical generation of hot carriers upon CPL excitation. This study not only offered a simple approach to enhance the photocatalytic performance of chiral plasmonic nanomaterials but also demonstrated the potential of chiral plasmonic materials for application in specific photocatalytic reactions, such as N2 fixation.

Diagnosis of DC-DC Converter Semiconductor Faults Based on the Second-Order Derivative of the Converter Input Current

The deployment of DC microgrids presents an excellent opportunity to enhance energy efficiency in buildings. Among other components, DC-DC converters play a crucial role in ensuring the interface between the microgrid and its energy generation, storage, and consumption components. However, the reliability of these energy conversion solutions remains somewhat limited. Adopting strategies for accurate monitoring and diagnostics of the DC-DC converter topologies that best suit each equipment’s constraints is, therefore, of critical relevance. Solutions available in the literature concerning fault diagnostics on DC-DC converters do not consider the application of such converters in the household and tertiary sector environments and associated constraints—cost effectiveness, robustness against parameter uncertainty of the converter model, and obviation of the need for historical data. On this basis, this paper presents a simple and effective fault diagnostic strategy, based on a time-domain analysis of the second-order derivative of the converter input current. Its implementation is straightforward and can be integrated into the pre-installed converter control unit. The unique features of the fault diagnostic algorithm show good results for a broad range of operating points, along with insensitivity against load transients and supply voltage fluctuations.

A hydrophilic porous graphene aerogel electrode with a large specific surface area for high-performance all-aqueous thermally regenerative batteries

All-aqueous thermally regenerative batteries (ATRBs) have shown great potential in harvesting low-grade waste heat. In this study, a hydrophilic porous graphene aerogel (GA) electrode developed by an ice template was developed for ATRBs to enhance electricity generation. The physicochemical property of GA was analyzed by traditional characterization. The main functional group of GA was N–H, which offered ATRBs a high hydrophilic surface. As a result of the ice templates, the diameter of pores in GA was almost lower than 4 nm, which provided a high specific area and good wettability. In addition, density functional theory calculations were carried out to verify the superiority of good electrical conductivity and strong adsorption on the cupric ions. Therefore, ATRB with GA achieved a competitive performance (a peak power density of 432 W/m2), illustrating great potential in the future thermoelectricity conversion application.

Anion-intercalation pseudocapacitance in oxygen vacancy-rich spinel-perovskite NiFe2O4-LaFeO3 nanocomposite for high energy density asymmetric supercapacitor application

Oxide nanomaterials have attracted significant attention as energy storage materials. The combination of spinel-perovskite oxides as nanocomposites creates dense oxygen vacancies (VO) at the hetero-interface. VO present in the complex oxides are indispensable for energy conversion applications. Herein, we demonstrated the one pot synthesis of spinel-perovskite NiFe2O4-xLaFeO3 nanocomposite and investigated the phase formation using variable temperature powder X-ray diffraction of the gel precursor. The role of oxygen-vacancy mediated tuneable redox transitions in NiFe2O4-xLaFeO3 nanocomposite has been understood. The anion-intercalation-based pseudocapacitance and the oxygen intercalation have been exploited for high-performance electrochemical energy storage. The NiFe2O4–2LaFeO3 exhibited a high specific capacity of 652 C g−1 at a current density of 2 A g−1. The fabricated NiFe2O4–2LaFeO3||NiCo2O4 asymmetric supercapacitor device (ASC) exhibited excellent cyclability over 20,000 cycles with superior capacity retention and high Coulombic efficiency (92 %) and achieved a high energy density of 42.5 Wh kg−1 at a power density of 1500 W kg−1. The presence of VO and the mixed-valence states of Fe2+/3+ were confirmed by XPS-depth profiling. The tuneable redox transition of Fe2+/3+ and VO contribute to the higher pseudocapacitance response.

Enhanced photoelectrochemcial activity of TiO2 nanoparticles by graphene intercalation

The photoelectronchemical (PEC) activity of the photocatalyst is largely dependent on the concentration and lifetime of the photogenerated carriers, however, these carriers are easily and quickly neutralized within the photocatalyst. To address this issue, we designed a superstructure of graphene-intercalated TiO2 nanoparticles (TiO2/G) by pyrolyzing octylamine-intercalated hexafluorotitanic acid hybrids. The inserted graphene accelerates photoelectron transfer and reduces the recombination of photogenerated carriers in the body, while maintains the structural stability. The TiO2/G hybrid composite exhibits a low carbon content of only 1.3 wt.%, a strong Ti-C chemical interaction between TiO2 and intercalated graphene, and a large surface area of 38.88 m2/g, nearly five times that of bare TiO2 (7.96 m2/g). The findings from the photocatalytic experiments indicate that the photocatalytic efficiency and photocurrent response of TiO2/G are twice and 4.22 times higher, respectively, compared to standard TiO2 nanoparticles. This indicates a substantial promise for the superstructure in photoelectrochemistry and energy conversion applications.

Modulating the Conductivity of Light-Responsive Ionic Liquid Crystals.

In this work, we describe the phase behaviour and the dielectric and conductivity response of new light-responsive ionic liquid crystals, ILCs, which can be applied as controllable electrolytes. The materials include two different dicationic viologens, the asymmetric 6BP18 and the symmetric EV2ON(Tf)2, containing bistriflimide as the counterions, mixed with 5% and 50% molar, respectively, of one new photoresponsive mesogen called CNAzO14. These mixtures exhibit liquid crystal behaviour, light responsiveness through the E-Z photoisomerisation of the azobenzene groups in CNAzO14, and strong dielectric responses. The 5%-CNAzO14/Ev2ON(Tf)2 mixture displays direct current conductivities in the 10-7 S·cm-1 range, which can be increased by a two-fold factor upon the irradiation of UV light at 365 nm. Our findings set the grounds for designing new smart ionic soft materials with nanostructures that can be tuned and used for energy conversion and storage applications.

Thermal conductivity reduction and crystal properties evolution in iron silicides induced by doping

Understanding the thermal transport behaviors in the crystal lattice is important for designing semiconducting materials in thermal management. In this work, we investigate the mechanism of the decrease in thermal properties of β-FeSi2 when Co dopant is introduced to the host crystal. The crystallite size decreases as Co doping increases from 0 to 5 %. The micro-strain and stress increase with increasing doping levels. The decrease in crystallite size and increase in micro-strain/stress indicate the origin of phonons scattering and lattice softening, leading to the reduction in thermal conductivity. This study provides insights into the correlation between the crystal properties evolution and thermal transport in metal silicide compounds which could be useful in thermal-to-energy conversion applications.

Inserting colloidal quantum dots into GaN mesa-array subsurface porous structures through electrochemical etching for display color conversion application

High-efficiency photon color conversion is an approach of great potential for implementing color display. Inspired by the observation of emission enhancement in a nanoscale cavity, a novel technique to fabricate an array of color converter by mixing colloidal quantum dots (QDs) with the electrolyte of an electrochemical etching (ECE) process is demonstrated. In this process, QDs flow with the electrolyte into the etched subsurface nanoscale porous structure (PS) and settle inside. Since the PS formation and hence QD insertion are controlled by the flow path of the applied electric current in the ECE process, this technique can be used for fabricating any graphic pattern. The nanostructure of such a QD-inserted mesa is examined to confirm QD insertion. Although only single-color mesa arrays are demonstrated in this paper, this technique can be used for fabricating a multiple-color mesa array if a QD or a light-emitting nanoparticle of higher thermal stability is available.

3D printing of phase change material-based Pickering emulsion gel for solar-thermal-electric conversion

The rapid global increase in the consumption of fossil energy had led to urgent environmental issues, thereby prompting vigorous efforts towards the development and application of renewable energy. The effective encapsulation of phase change materials (PCMs) is crucial and indispensable for achieving high-performance solar-thermal energy harvesting and storage. However, challenges persist in the manufacturing of PCMs encapsulations with customizable and intricate structures to meet diverse scenarios. Herein, a PCMs Pickering emulsion gel ink, based on lignocellulosic nanofibers (LCNFs)/graphene oxide (GO) nanosheets stabilized paraffin, has been prepared to fabricate customized PCMs using 3D printing techniques for solar-thermal-electric conversion applications. The micro-nano matrix consisting of LCNFs and GO nanosheets provides a stable oil/water (O/W) interface, limits movements and deformability of paraffin microsphere, thereby increasing the viscosity and stiffness of the PCMs Pickering emulsion gel ink to ensure its excellent rheological property. Moreover, the LCNFs enhance printability and shape fidelity of the ink as interfacial stabilizer and viscosity modifier, which facilitates the manufacture of various 3D geometries. As a result, the designed concave PCMs solar harvester not only exhibits exceptional solar-to-thermal conversion efficiency, but also effectively mitigates heat loss and enables efficient heat storage for electricity generation. Our work demonstrates a new way toward utilization of LCNFs as PCMs emulsion stabilizers and encapsulants in PCMs and the fabrication customized PCMs architectures for solar-thermal-electric conversion applications using 3D printing techniques.

Fabrication of boron nitride/copper oxide@multi-walled carbon nanotubes composites for enhancing heat transfer and photothermal conversion of phase change materials

To realize the efficient storage and conversion of solar energy by phase change materials (PCMs), low photothermal conversion efficiency and poor heat transfer performance remain great challenges. Herein, polyethylene glycol (PEG)-based composite PCMs with excellent photothermal conversion performance and exceptional thermal management capability were obtained by using boron nitride/copper oxide@multi-walled carbon nanotubes (BN/CuO@MWCNTs) as the thermal conductive and photothermal conversion enhancement fillers. The results indicate that owing to the bridging effect, the introduction of CuO and MWCNTs on the BN surface can construct additional heat transfer paths, resulting in a high thermal conductivity of up to 2.35 W/(m·K) for the as-prepared PEG/BN/CuO@MWCNTs composite, which is about 9-folds enhancement than pristine PEG. Simultaneously, the supercooling degree of PEG in PEG/BN/CuO@MWCNTs is effectively suppressed due to the synergistic nucleation effect of BN, CuO and MWCNTs. Additionally, the PEG/BN/CuO@MWCNTs composites not only exhibit a high latent-heat capacity of 154.5 J/g and a high photothermal conversion efficiency of 92.2 %, but also show favorable shape stability and durable reliability. This work offers a workable solution for the synergistic enhancement of photothermal conversion and thermal management, which can effectively promote the practical application in solar energy conversion and storage.

Computational insights into structural, electronic, optical and thermoelectric features of ternary chalcogenide Ca2GeX4 (X=S, Se, Te) compounds

The advancements in materials engineering for clean energy and greenhouse gas reduction has attracted global attention. Furthermore, the distinct electrical and optical properties of ternary chalcogenides are critical for their application in solar energy conversion. In this study, the electronic, optical, thermodynamic, and thermoelectric transport properties of the ternary chalcogenide Ca2GeX4 (X = S, Se, and Te) compounds are comprehensively investigated using the density functional theory-based WIEN2k package. The findings indicate that ternary chalcogenide Ca2GeX4 compounds possess substantial band gaps and display strong covalent bonding characteristics. Analysis of the density of states reveals minimal impact from S-s and S-p states, while highlighting the significance of Ca-s and Ge-s states. The investigated materials show significant UV absorption with reflectance between 30 and 40 % which peaks at 13.5 eV at about 65 %, confirming the optical properties of the ternary chalcogenide Ca2GeX4. The positive Seebeck coefficient suggests that holes are the primary charge carriers in tested materials, with thermal energy rising in accordance with the chalcogenide's atomic number. Several thermoelectric properties that demonstrate the suitability of these materials for thermoelectric applications were also discussed. Overall, the findings confirm the thermoelectric and optoelectronic properties of Ca2GeX4 materials, which may facilitate the creation and development of effective optoelectronic devices.

Water structures and anisotropic dynamics at Pt(211)/water interface revealed by machine learning molecular dynamics

Abstract Water molecules at solid–liquid interfaces play a pivotal role in governing interfacial phenomena that underpin electrochemical and catalytic processes. The organization and behavior of these interfacial water molecules can significantly influence the solvation of ions, the adsorption of reactants, and the kinetics of electrochemical reactions. The stepped structure of Pt surfaces can alter the properties of the interfacial water, thereby modulating the interfacial environment and the resulting surface reactivity. Revealing the in situ details of water structures at these stepped Pt/water interfaces is crucial for understanding the fundamental mechanisms that drive diverse applications in energy conversion and material science. In this work, we have developed a machine learning potential for the Pt(211)/water interface and performed machine learning molecular dynamics simulations. Our findings reveal distinct types of chemisorbed and physisorbed water molecules within the adsorbed layer. Importantly, we identified three unique water pairs that were not observed in the basal plane/water interfaces, which may serve as key precursors for water dissociation. These interfacial water structures contribute to the anisotropic dynamics of the adsorbed water layer. Our study provides molecular-level insights into the anisotropic nature of water behavior at stepped Pt/water interfaces, which can influence the reorientation and distribution of intermediates, molecules, and ions—crucial aspects for understanding electrochemical and catalytic processes.

Power absorption and flow-field characteristics analysis for oscillating coaxial twin-buoy wave energy converter by using CFD

The energy conversion capacity of wave energy conversion devices highly depends on the hydrodynamic characteristics of the energy-harvesting structure. To investigate the effect of hydrodynamic performance on the power conversion characteristics, a twin-buoy wave energy converter (WEC) was investigated by using a three-dimensional numerical wave pool based on the Computational Fluid Dynamics (CFD) method. Several factors are examined, including the elasticity coefficient of the anchor chain, the bottom configuration of the floating body, and the power take-off (PTO) damping coefficient. The heave displacement, heave velocity, and heave force of the converter are calculated under specific wave parameters, and the flow field cloud diagram during the heave motion is analyzed. The results indicate that a wave energy converter with a hemispherical floating body exhibits the best kinematic performance. The influence of the mechanical damping coefficient on the energy conversion performance of the device is studied. By appropriately reducing the mechanical damping coefficient, the energy capturing capability of the device can be increased to a certain extent. These findings can serve as a theoretical basis for the application of deep-water wave energy conversion in engineering and the optimization of future WEC designs.

High Performance and Selective Sequestration of Cd(II) from Water by Layered Thiophosphate.

The extensive use of toxic cadmium (Cd) in energy conversion and industrial applications ranging from solar cells and battery appliances to paints and pigments contaminates water bodies. However, the upper limit of Cd contamination in drinking water is to be only 3 ppb by the WHO and 5 ppb by the USA-EPA, which underscores the need for cost-effective, efficient, and ppb level capture of Cd from contaminated water. Leveraging the selectivity due to Lewis's hard-soft acid-base (HSAB) theory, we have achieved swift and highly selective capture of Cd(II) ions from aqueous mediums using layered potassium manganese thiophosphate (K-MnPS3). K-MnPS3 effectively removes Cd(II) ions from extremely dilute aqueous solutions (ppb levels), achieving a maximum sorption capacity of 405.43 mg/g and a removal rate exceeding 97% within 20 min. Even in the presence of competing ions such as Na+, Mg2+, Ca2+, and Pb2+, K-MnPS3 remains selective. Additionally, it operates efficiently across a wide pH range (1.78-11.19) with a high distribution coefficient (∼104 mL/g). Breakthrough experiments using a 1 wt % K-MnPS3 and 99 wt % sand column showed complete breakthrough of Cd(II) after 62 h, leading K-MnPS3 as a promising candidate for Cd(II) removal from industrial effluents.

Piezoelectricity in NbOI2 for piezotronics and nanogenerators

2-dimensional (2D) piezoelectric materials have gained significant attention due to their potential applications in flexible energy harvesting and storage devices. Recently, niobium oxide dihalides NbOI2 stands out as a multifunctional anisotropic semiconductor family with an exceptionally high lateral piezoelectric constant (~21.8 pm/V), making it a promising candidate for energy conversion applications. Here we report the experimental observation of anisotropic in-plane piezoelectricity in multilayer NbOI2. Current-voltage relationships reveal a significant piezotronic effect in two typical crystalline orientations. Additionally, cyclic tensile and release experiments demonstrate an intrinsic current output of up to 140 pA when subjected to a tensile strain of 0.51%. A flexible piezoelectric nanogenerator prototype is demonstrated on the human finger and wrist, which opens up new avenues for the development of wearable electronic devices and provides valuable insights for further exploration in this field.

Constructing type II heterojunction of 2D/1D Pg-C3N4/Ag3VO4 nanocomposite with high interfacial charge separation for boosting photocatalytic CO2 reduction under solar energy

The well-designed, template-free synthesis of 2D protonated g-C3N4 nanosheets (Pg-C3N4) coupled with novel 1D Ag3VO4 nanorods has been investigated to construct 2D/1D interface heterostructures with strong electrostatic interactions between the positively charged 2D Pg-C3N4 nanosheets and the negatively charged 1D Ag3VO4 nanorods. The coupling of Pg-C3N4 and Ag3VO4 with desirable characteristics resulted in a 2D/1D interface heterojunction with a type II charge carrier transfer mechanism, effectively maintaining and utilizing charge carriers. The 2D/1D Pg-C3N4/Ag3VO4 exhibited remarkable photocatalytic performance for CO2 conversion with H2O, resulting in maximum CH4 and dimethyl ether (DME) production of 352.3 and 130.9 µmol/g-cat, respectively. A quantum yield of 0.23 % for CH4 generation was achieved over the 2D/1D Pg-C3N4/Ag3VO4, which was 2.9 and 1.4 times higher than that of the Pg-C3N4 and Ag3VO4 samples, respectively. The improvement in photocatalytic performance primarily stems from the effective interaction between Pg-C3N4 and ternary Ag3VO4, leading to enhanced transfer and separation of photoinduced charge carriers through the creation of a type II heterojunction. The findings of this study are useful in designing template-free heterojunctions for photocatalytic CO2 conversion and other solar energy applications.

Rational design of Er2O3/ZnS as highly competent electrocatalyst for OER application

The fabrication of an extremely productive, inexpensive and prominent electrocatalyst is required to improve the slow oxygen evolution reaction (OER). Here, a hydrothermal approach was utilized to fabricate Er2O3/ZnS composite as a competent electrode material for the purpose of efficient water splitting. The various analytical tools were used to evaluate morphology, crystallinity, functionality, surface area, and thermal stability of the reported materials. The large surface area of the Er2O3/ZnS composite (61.06 m2 g−1), makes it a suitable candidate for carrying out the OER process. Moreover, the electrochemical study for Er2O3/ZnS composite was conducted on nickel foam (NF) as a substrate to determine the electrolytic nature. The electrochemical study showed that the synthesized composite responds to an impressive overpotential (260 mV) and low Tafel value (40 mV dec−1) at an ideal current density (j) of 10 mA cm−2. The Er2O3/ZnS composite exhibits a reduced onset potential of approximately 1.31 V and exceptional durability of about 30 h. The electrochemical observation suggests that incorporating Er2O3 into ZnS resulted in an enlarged surface area and enhanced active regions which reduce the resistance and promote the rapid binding of electrolyte ions. The composite (Er2O3/ZnS) developed by this approach can be utilized in various energy conversion and storage applications.

BAs/BlueP van der Waals heterostructures for photovoltaic and thermoelectric applications

The advancement of novel energy materials, encompassing photovoltaic and thermoelectric materials, assumes paramount significance in ameliorating the energy crisis and proactively combating climate change. The BAs/BlueP van der Waals heterostructure (vdWH), characterized by its outstanding optical absorption properties, high power conversion efficiency (PCE), and excellent thermoelectric performance, offers novel insights into the advancement of materials for photonic and thermoelectric applications. We have engineered a vdWH by combining BAs and BlueP, and conducted a comprehensive investigation of its electronic, optical, and thermoelectric properties. The BAs/BlueP vdWH demonstrates excellent thermodynamic and kinetic stability with type I band alignment, facilitating rapid interlayer electron-hole recombination. The remarkable optical absorption capability within the visible and ultraviolet (UV) spectral regions, coupled with an outstanding power conversion efficiency reaching up to 22.35 % under strain, firmly establishes the potential for utilization in photovoltaic conversion applications. At 1000 K, the significant ZT value (1.25) and high thermoelectric conversion efficiency (19.45 %) provide the theoretical foundation for its application in the field of thermoelectrics.

Enhancing Crystallinity and Magnetic Properties of Cobalt Ferrite Nanoparticles via Thermal Oxidation

AbstractCobalt ferrite (CFO) nanoparticles (NPs) are highly promising for data storage, energy conversion, permanent magnets, and biomedical applications owing to their exceptional magnetic properties. However, the presence of phase impurities (particularly FeO and CoO) can severely degrade their magnetic properties, hindering their practical use. Here, we present a simple post‐synthesis oxidation approach to address this challenge. Our method involves the thermal decomposition of Fe−Co oleate followed by oxidation using trimethylamine N‐oxide. The results reveal the effective elimination of FeO and CoO impurities and the formation of spinel ferrite crystal structures post‐oxidation with no change in morphology or size. Magnetic measurements demonstrate a significant enhancement in magnetic properties (e. g., magnetic saturation, coercivity, and blocking temperature) in oxidized CFO NPs compared to the non‐oxidized counterparts, indicative of the recovered ferrimagnetic structure upon post‐synthesis oxidation. As expected, the restoration of the ferrimagnetic structure, resulting in improved magnetic anisotropy, led to decreased SAR values as the nanoparticles moved away from the optimal anisotropy range. The study underscores the necessity of post‐synthesis oxidation for ensuring phase purity and enhancing the magnetic properties of CFO NPs, irrespective of the synthesis method. This approach offers a promising route for producing highly functional magnetic nanoparticles for practical applications.

Dual internal electric field induced by Ni3C selectively deposited onto Mn2O3 on faceted BiVO4 for boosting photocatalytic oxygen evolution

The oxidation reaction between charge and water for photocatalyst has restricted overall water splitting efficiency. Herein, the non-noble-metal Ni3C acting as an electron sink were selectively deposited onto Mn2O3 on faceted BiVO4 via electrostatic self-assembly, synergistically creating faceted heterostructure with dual internal electric field (IEF) for photocatalytic water oxidation. Resultantly, a remarkable visible light-driven photocatalytic O2 evolution rate was observed to be 2736.5 μmol g−1 h−1 with an apparent quantum yield of 5.57 % at 400 nm. The significantly improved activity mainly stemmed from the giant dual IEF, dramatically accelerating exciton separation and prolonging the lifetime of charge carriers. Moreover, the photocatalysts without activity attenuation were considerably stable and reused with recyclability utilizing the magnetic nature in practical application. By combining with the self-induced IEF by exposed {001} facet of BiVO4 for improving photocatalytic activity, this work could throw light on the design of faceted heterostructure in solar energy conversion application.