Energy Conversion Devices Research Articles

Ultra‐High DC and Low Impedance Output for Free‐Standing Triboelectric Nanogenerator

AbstractThe free‐standing triboelectric nanogenerator (F‐S TENG) is demonstrated to be an efficient energy conversion device. However, limited by the inherent features of high‐voltage, low alternating current and high output impedance, TENGs suffer from inefficient energy utilization and difficulties in practical applications. Therefore, the efficient harvest of mechanical energy and optimization of output are currently critical issues for TENGs. Here, a strategy is proposed for optimizing the inherent features by coupling F‐S TENG to a capacitor auto‐conversion circuit (CAC). For the first time, a specific idea is proposed explicitly to reduce the output impedance by the management circuit. Eventually, a high current density of 32 A m−2 and a charge density of 1.75 mC m−2 are achieved, which is 8.78 times higher than previous works. The power density and energy density reach to 124 W m−2 and 252 mJ m−2 under 470 and 150 Ω respectively. Then, 5000 LEDs and two lamps rated at 220 V and 50 W are manually illuminated. The resulting pulse output is utilized as a trigger source for the thyristor, enabling DC contactless switching. This work provides a novel approach to realize high‐performance DC output of TENGs and effectively reduce external load impedance.

RGO and CNTs synergistically modified mixed-phase nickel sulfide nanohybrids with abundant redox-active sites for high-performance hybrid supercapacitors

Hybrid supercapacitors (HSCs) integrating high energy density and power density have great prospects for applications in new high-performance energy storage and conversion devices. Herein, a novel reduced graphene oxide (RGO) and carbon nanotubes (CNTs) synergistically modified mixed-phase nickel sulfide (NiS/NiS2) nanohybrids (NSRCs) were successfully designed and synthesized by a facile one-step solvothermal method. Benefiting from the high conductivity and high specific surface area of carbon materials and the high specific capacity of nickel sulfide, as well as the stable nanostructures constructed by the synergistic effect of multiple components, the synthesized novel NSRCs nanohybrids exhibit impressive electrochemical performances, such as high specific capacity of 178.2 mAh g−1 (1604.1 F g−1) at 0.6 A g−1, excellent rate capability (57.3 % at 20 A g−1). Furthermore, the assembled hybrid supercapacitors (NSRC-24//AC HSC) with optimal NSRC-24 electrode and activated carbon (AC) electrode imparted a high energy density of 44.2 Wh kg−1 at a power density of 359.2 W kg−1 and excellent cycling stability (98.1 % capacity retention after 12,000 cycles at 5 A g−1). Thus, the synthesized novel NSRCs nanohybrids are highly promising candidates as advanced electrode materials for aqueous high-performance energy storage devices.

Ti3C2 MXene Nanosheets/Vanadium Nitride@Carbon Composite Electrodes for High-Performance Lithium-Ion Batteries

Lithium-ion batteries have delivered outstanding charge storage performance due to their high energy density and low cost and also more specialized energy conversion device for next-generation electrical appliances. Herein, we offered the ultrathin Ti3C2 MXene (titanium carbide) nanosheets/vanadium nitride (VN)@carbon (C) nanocomposites for lithium-ion storage application as a high-capacity anode material. The proposed anode material is Ti3C2 MXene nanosheets/VN@C composite as synthesized via chemical precipitation. The real-time half-cell of Ti3C2 MXene nanosheets/VN@C composite shows the excellent initial discharge specific capacity of 1237 mAh g-1 at a current density of 0.1 A g-1 with a reverse rate capacity of 685 mAh g-1. The high specific capacity of 645 mAh g-1 has been attained even after 500 cycles at a current density of 0.1 A g-1. This type of rich reverse rate capacity and stability of the anode electrode is responsible due to the high conductivities and surface areas of Ti3C2 MXene nanosheets/VN@C composite, which is provided easy accessibility of Li+ ions.

Nd-doping-induced perovskite/Ruddlesden-Popper heterointerfaces boost the ORR activity and CO2 tolerance for SrFeO3-δ-based cathode

The development of cathode materials with high oxygen reduction reaction (ORR) activity is crucial to realize the wide application of solid oxide fuel cells. Nd-doped SrFeO3-δ (SNF) two-phase nanocomposite was fabricated by a dopant-induced in situ self-assembly process. The SNF nanocomposite comprises 63.4 wt% perovskite main phase (P–SNF) and 36.6 wt% Ruddlesden-Popper second phase (RP-SNF). The average thermal expansion coefficient (TEC) of SrFeO3-δ is reduced by 36.5 % and down to 13.9 × 10−6 K−1. At 750 °C, SNF demonstrates an impressive output power of 779 mW cm−2, which is twice that of the single-phase SrFeO3-δ. The superior performance stems from the heterointerface effect of the in situ self-assembled two phases. This effect increases the content of oxygen vacancies, thereby enhancing both chemical oxygen surface exchange coefficient and bulk diffusion coefficient. Moreover, the SNF composite exhibits excellent CO2 tolerance than the single-phase SrFeO3-δ. This work presents a promising avenue for exploring multifunctional materials through interface engineering, offering new possibilities for future energy conversion devices.

Self-standing electrospun Co/Zn@N-doped carbon nanofiber electrode for highly stable liquid and solid-state rechargeable zinc-air batteries and performance evaluated by scanning electrochemical microscopy at various temperatures

Zinc-air batteries (ZABs) as promising energy storage technologies have shown immense advantages of high energy density, abundant zinc reserves, low cost, and high safety. However, the sluggish oxygen reduction reaction (ORR) kinetics at the cathode still limits their overall performances. Herein, we fabricated a self-supported N-doped Co/Zn-carbon nanofiber membrane (Co/Zn@NCF) with superior activity and durability for the ORR. The liquid ZABs based on Co/Zn@NCF catalysts exhibited a cycling life of over 666 h with a charge/discharge voltage difference of 0.64 V and a voltage efficiency of 66 %. The fabricated flexible solid-state ZAB enables it to be stably charged and discharged under different bending angles. Strikingly the temperature-controlled scanning electrochemical microscopy (SECM) was developed to probe the local activity and selectivity of membrane-like Co/Zn@NCF at a submicrometer scale. This study provides an effective way for the development of self-supported catalysts for energy conversion devices and offers the in-operando technique for the analysis of catalysts in various operating temperatures.

Optimization and test study of centripetal pump in disc-stack centrifuge based on flow field analysis

BackgroundDisc-stack centrifuges are widely used in various production areas, and the centripetal pump serves as its energy conversion device, which saves energy. MethodsBased on the condition of constant fluid velocity moment in the flow channel of centripetal pump, redrawn the shape of the flow channel while keeping the height constant, to achieve the improvement of discharge performance. Significant findingsThe optimized centripetal pump has a reasonable static pressure distribution, a wider velocity distribution and a more uniform velocity gradient distribution, and the pressure drop is reduced by 4.8 % compared with the original structure. The performance enhancement of the centripetal pump positively affects the performance of the whole machine. The centrifuge now reaches a higher efficiency (96 %), and can effectively reduce the power consumption, wear, and vibration during operation, which can provide reference for the design and optimization of centripetal pumps of disc-stack centrifuges.

Facile pyrolysis synthesis of abundant FeCo dual-single atoms anchored on N-doped carbon nanocages for synergistically boosting oxygen reduction reaction

Single-atom transition metal-based nitrogen-doped carbon (M−Nx−C) is regarded as high-efficiency and cost-effectiveness alternatives to replace noble metal catalysts for oxygen reduction reaction (ORR) in renewable energy storage and conversion devices. In this work, rich FeCo dual-single atoms were efficiently entrapped into N-doped carbon nanocages (FeCo DSAs-NCCs) by simple pyrolysis of the bimetallic precursors doped zeolitic imidazolate framework-8 (ZIF-8), as affirmed by a series of characterizations. The graphitization degree of the N-doping carbon substrate was regulated by modulating the pyrolysis temperature and the types of the metal salts. The typical catalyst substantially improved the alkaline ORR performance, with the onset potential (Eonset) of 0.99 V (vs. RHE) and half-wave potential (E1/2) of 0.88 V (vs. RHE). Ultimately, the catalyst-assembled Zn-air battery possessed a higher open-circuit voltage of 1.501 V, larger power density of 123.7 mW cm−2, and outstanding durability for 150 h. This study provides a guide on developing ORR catalysts for electrochemical energy conversion and storage technology.

Toward understanding the microstructure characteristics, phase selection and magnetic properties of laser additive manufactured Nd-Fe-B permanent magnets

Nd-Fe-B permanent magnets play a crucial role in energy conversion and electronic devices. The essential magnetic properties of Nd-Fe-B magnets, particularly coercivity and remanent magnetization, are significantly influenced by the phase characteristics and microstructure. In this work, Nd-Fe-B magnets were manufactured using vacuum induction melting (VIM), laser directed energy deposition (LDED) and laser powder bed fusion (LPBF) technologies. The microstructure evolution and phase selection of Nd-Fe-B magnets were then clarified in detail. The results indicated that the solidification velocity (V) and cooling rate (R) are key factors in the phase selection. In terms of the VIM-casting Nd-Fe-B magnet, a large volume fraction of the α-Fe soft magnetic phase (39.7 vol.%) and Nd2Fe17B x metastable phase (34.7 vol.%) are formed due to the low R (2.3 × 10−1 °C s−1), whereas only a minor fraction of the Nd2Fe14B hard magnetic phase (5.15 vol.%) is presented. For the LDED-processed Nd-Fe-B deposit, although the Nd2Fe14B hard magnetic phase also had a low value (3.4 vol.%) as the values of V (<10−2 m s−1) and R (5.06 × 103 °C s−1) increased, part of the α-Fe soft magnetic phase (31.7 vol.%) is suppressed, and a higher volume of Nd2Fe17B x metastable phases (47.5 vol.%) are formed. As a result, both the VIM-casting and LDED-processed Nd-Fe-B deposits exhibited poor magnetic properties. In contrast, employing the high values of V (>10−2 m s−1) and R (1.45 × 106 °C s−1) in the LPBF process resulted in the substantial formation of the Nd2Fe14B hard magnetic phase (55.8 vol.%) directly from the liquid, while the α-Fe soft magnetic phase and Nd2Fe17B x metastable phase precipitation are suppressed in the LPBF-processed Nd-Fe-B magnet. Additionally, crystallographic texture analysis reveals that the LPBF-processed Nd-Fe-B magnets exhibit isotropic magnetic characteristics. Consequently, the LPBF-processed Nd-Fe-B deposit, exhibiting a coercivity of 656 kA m−1, remanence of 0.79 T and maximum energy product of 71.5 kJ m−3, achieved an acceptable magnetic performance, comparable to other additive manufacturing processed Nd-Fe-B magnets from MQP (Nd-lean) Nd-Fe-B powder.

Bioinspired Hollow/Hollow Architecture with Flourishing Dielectric Properties for Efficient Electromagnetic Energy Reclamation Device.

The exploitation of advanced electromagnetic functional devices is perceived as the effective prescription to deal with environmental contamination and energy deficiency. From the perspective of observing and imitating nature, pine branch-like zirconium dioxide/cobalt nanotubes@nitrogen-doped carbon nanotubes are synthesized victoriously through maneuverable electrospinning process and follow-up thermal treatments. In particular, introducing carbon nanotubes on the surface of hollow nanofibers to construct hierarchical architecture vastly promoted the material's dielectric properties by significantly augmenting specific surface area, generating abundant heterogeneous interfaces, and inducing the formation of defects. Supplemented by the synergistic effect between each constituent, ultra-strong attenuation capacity and perfect impedance matching characteristics are implemented simultaneously, and jointly made contributions to the splendid microwave absorption performance with a minimum reflection loss of -67.9dB at 1.5mm. Moreover, this fibrous absorber also exhibited promising potential to be utilized as a green and efficient electromagnetic interference shielding material when the filler loading is enhanced. Therefore, this design philosophy is destined to inspire the future development of energy conversion and storage devices, and provide theoretical direction for the creation of sophisticated electromagnetic functional materials.

Hetero-structured composite cathodes by electrospinning with high CO2-poisoning tolerance for solid oxide fuel cells

The sluggish oxygen reduction reaction (ORR) kinetics significantly hinder the development of intermediate temperature solid oxide fuel cells (IT-SOFC). Herein, a heterostructure composite fibers cathode composed of Ba0.9La0.1Co0.7Fe0.2Nb0.1O3-δ and Sm0.2Ce0.8O2-δ (BLCFN-SDC fibers) has been co-synthesized by electrospinning method, which exhibited excellent electrochemical activity, CO2 tolerance and long-term stability. The polarization resistance (Rp) of BLCFN-SDC fibers cathode at 700 °C is only 0.050 Ω cm2, much lower than those of single-phase BLCFN fibers (0.069 Ω cm2) and BLCFN powders (0.073 Ω cm2). Such improvement can be attributed to the extended three-phase boundary (TPB) and more exposed oxygen reduction reaction (ORR) active sites. Besides, the unique fibers structure provides continuous charge transport paths, which improve its conductivity. Furthermore, BLCFN-SDC fibers exhibits excellent CO2 tolerance in high concentration CO2 atmosphere, benefited from the low CO2 adsorption characteristics and stability of SDC. The results suggest that such heterostructure fibers cathode with excellent ORR activity and CO2 durability might provide a novel method to design efficient catalysts for SOFCs and other energy conversion devices.

Unraveling the Emerging Photocatalytic, Thermoelectric, and Topological Properties of Intercalated Architecture MZX (M = Ga and In; Z = Si, Ge and Sn; X = S, Se, and Te) Monolayers.

The continuous advancements in studying two-dimensional (2D) materials pave the way for groundbreaking innovations across various industries. In this study, by employing density functional theory calculations, we comprehensively elucidate the electronic structures of MZX (M = Ga and In; Z = Si, Ge, and Sn; X = S, Se, and Te) monolayers for their applications in photocatalytic, thermoelectric, and spintronic fields. Interestingly, GaSiS, GaSiSe, InSiS, and InSiSe monolayers are identified to be efficient photocatalysts for overall water splitting with band gaps close to 2.0 eV, suitable band edge positions, and excellent optical harvest ability. In addition, the InSiTe monolayer exhibits a ZT value of 1.87 at 700 K, making it highly appealing for applications in thermoelectric devices. It is further highlighted that GaSnTe, InSnS, and InSnSe monolayers are predicted to be 2D topological insulators (TIs) with bulk band gaps of 115, 54, and 152 meV, respectively. Current research expands the family of 2D GaGeTe materials and establishes a path toward the practical utilization of MZX monolayers in energy conversion and spintronic devices.

Boosting the oxygen bifunctional activity on cobalt nanocrystals/RGO with extended durability

Nanoengineering effective bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains a major challenge in improving the performance of electrochemical energy conversion devices. In this study, we present a simple synthesis route for producing Co-Nx crystals that are effectively arranged on reduced graphene oxide layers (Co–N/RGO) through mechanochemical treatment. The Co–N/RGO catalyst performs well as a bifunctional oxygen electrocatalyst. Specifically, the Co–N/RGO-700 has an earlier ORR onset (0.91 V) and a half-wave potential (0.79 V) with a higher kinetic current density of 6.6 mA cm−2 than Pt/C, as well as a lower overpotential (430 mV) and Tafel slope (115 mV dec−1) for the OER. These results demonstrate outstanding performance compared to reported Co-based catalysts. Theoretical modeling and experimental results explore the Co–N/RGO active sites, as well as the vital role of electronic structure, abundant N content, and surface defects, confirming it as a potential electrode material for energy conversion applications.

Investigating the physico-chemical and electrochemical properties of various aliovalent cations doped ceria powders for electrolytic applications in solid oxide fuel cells

Solid oxide fuel cells (SOFCs) are one of the most efficient energy conversion devices, yet their high operating temperatures have caused a bottleneck towards their commercialization. Due to sufficient conductivity and stability below 600 °C, doped ceria is under investigation for electrolytic applications in SOFCs. During this study, starting with Ce0.8Sm0.2O2-δ, 5% of Sm3+ was replaced by dopants of varying valencies and sizes giving Ce0.8Sm0.15X0.05O2-δ (where X = Bi3+, Mg2+, Li+), thereby aiming to keep the total dopant concentration constant. The structure-property relationship was studied using a number of techniques including XRD, Raman spectroscopy, FTIR spectroscopy and temperature dependent EIS. XRD indicated the presence of a minor phase belonging to MgO for the Mg2+ co-doped sample. Raman spectroscopy showed the presence of δ-Bi2O3 for Bi3+ doped SDC. Based on the quantitative analysis of Raman data we concluded that the materials were multi-phasic and co-dopants addition did not have a noticeable influence especially on defect concentration. In EIS data, measured from of 550–750 °C, change in conductance behavior was shown by Arrhenius plots for SCB and SCM when the test temperature was raised over 650 °C, possibly reflecting the combined conduction due to the additional phases along with SDC for these samples. Poor solubility of the non-rare earth metal ions into the ceria lattice was observed. This study suggests the need of a comprehensive analysis of doping mechanism preferably by synchrotron-based techniques to effectively incorporate low-cost non-rare earth metals into ceria lattice.

Self‐Configured Composites of Ruddlesden‐Popper Perovskite and Pr6O11 as Efficient and Durable Air Electrodes for Reversible Protonic Ceramic Electrochemical Cells

AbstractA breakthrough in the development of air electrodes is critical to minimizing the performance deterioration of reversible protonic ceramic electrochemical cells (R‐PCECs), which have demonstrated the potential to be the most promising electrochemical device for energy storage and conversion. Here, a Co‐doped Ruddlesden‐Popper (RP) perovskite with a nominal formula of Pr2Ni0.6Co0.4O4‐δ is reported, which is self‐configured into a composite of Pr4Ni1.8Co1.2O10‐δ (PNCO, 89.57 wt.%) and Pr6O11 (10.43 wt.%), suggested by the X‐ray diffraction refinement. The composite electrodes exhibit improved electrochemical activity with an area‐specific resistance of 0.33 Ω cm2 at 600 °C after being treated with wet air, due primarily to the raised surface exchange, bulk diffusion capabilities, and the increasing amount of Pr6O11 with catalytic activity. The R‐PCECs with the composite electrodes achieve a maximum power density of 1.32 W cm−2 and a current density of 3.09 A cm−2 at 1.3 V with acceptable Faradaic efficiencies at 650 °C. Furthermore, the composite electrodes show benign operational durability in fuel cell mode (‐0.5 A cm−2 for 167 h) and electrolysis mode (+0.5 A cm−2 for 176 h), and promising cycling stability (+/‐0.5 A cm−2) of 124 h at an interval of 2 h.

Enhanced Heat Flow between Charged Nanoparticles and an Aqueous Electrolyte.

Heat transfer through the interface between a metallic nanoparticle and an electrolyte solution has great importance in a number of applications, ranging from nanoparticle-based cancer treatments to nanofluids and solar energy conversion devices. However, the impact of the surface charge and dissolved ions on heat transfer has been scarcely explored so far. In this study, we compute the interface thermal conductance between hydrophilic and hydrophobic charged gold nanoparticles immersed in an electrolyte using equilibrium molecular dynamics simulations. Compared with an uncharged nanoparticle, we report a 3-fold increase of the Kapitza conductance for a nanoparticle surface charge of +320 mC/m2. This enhancement is shown to be approximately independent of the surface wettability, charge spatial distribution, and salt concentration. This allows us to express the Kapitza conductance enhancement in terms of the surface charge density on a master curve. Finally, we interpret the increase of the Kapitza conductance as a combined result of the shift of the water density distribution toward the charged nanoparticle and an accumulation of the counterions around the nanoparticle surface which increase the Coulombic interaction between the liquid and the charged nanoparticle. These considerations help us to apprehend the role of ions in heat transfer close to electrified surfaces.

Mechanism of carbon nanotube growth in expanded graphite via catalytic pyrolysis reaction using carbores P as a carbon source.

Carbon nanotubes (CNTs) had potential applications in energy conversion and storage devices, and it could be prepared by expanded graphite loaded with catalyst at high temperature, however, the mechanism of carbon nanotube growth in expanded graphite need further confirmation. In this work, carbon nanotubes' in situ growth in expanded graphite (EG) were prepared via catalytic pyrolysis reaction using carbores P as a carbon source and Co(NO3)3•6H2O as a catalyst. The results of X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscope (EDS) indicated the carbon nanotubes could generate in, EG with the presence of carbores P as a carbon source and cobalt nitrate as a catalyst. More interestingly, the growth mechanism of carbon nanotubes could be concluded by the results of differential thermal analysis-thermogravimetry-mass spectrometry (DTA-TG-MS) and X-ray photoelectron spectroscopy (XPS) analysis. The pyrolysis products of carbores P were mainly hydrocarbon gas such as CH4 gas, which reacts with Co(NO3)3·6H2O catalyst to reduces CoOx to Co particles, then the carbon form pyrolysis was deposited the on the surface catalyst Co particles and, after continuous solid dissolution and precipitation, carbon nanotubes were at last generated in EG at last.

Unlocking efficiency in oxygen reduction reaction: Synergistic edge dopants of nitrogen and boron in carbon nano onions

Oxygen reduction reaction (ORR) is a crucial process for energy conversion and storage devices. Despite platinum (Pt) being the state-of-the-art material for ORR, the limited performance of Pt-based catalyst, Pt scarcity, and vulnerability of global supply chains for critical minerals, have made it imperative to develop alternative electrocatalysts that either contain no precious metals at all or require only a very low loading of these valuable resources. In this study, we demonstrate that the incorporation of co-dopants, nitrogen (N) and boron (B), with a dissimilar electronegativity is a promising approach to develop metal-free electrocatalysts for ORR. We discovered that the interaction between N and B plays a vital role in both (i) incorporating the dopants in high-curvature carbon nano-onions (CNOs) and (ii) promoting ORR performance. Tuning the annealing temperature was crucial to achieve a desirable N-B chemical configuration and synergistic effects of N and B on ORR catalysis. Our investigation revealed that N,B-doped CNOs prepared at 700 °C exhibit the best ORR performance in 0.1 M KOH with a dominant 4-electron pathway and excellent durability. Based on X-ray photoelectron spectroscopy (XPS), Raman analysis, and high-resolution scanning transmission electron microscopy (HR-STEM), we conclude that abundant N and B sites, especially N-C-B (isolated) sites, at the edges in conjunction with high surface activity of CNOs are responsible for such outstanding performances. This study provide insights into the design of metal-free catalysts for efficient ORR catalysis, and the importance of alternative electrocatalysts in the current global supply chain disrutipn scenario.

Bifunctional Ce0.9Gd0.09M0.01O2−δ (M = Fe, Cu) interlayers with micro-doping for high-performance solid oxide fuel cells

Solid oxide fuel cells (SOFCs) are promising, sustainable and efficient electrochemical energy conversion devices. The dense and thin interlayer prepared at low sintering temperature is essential to avoid detrimental reaction between cobalt-containing cathode and zirconia-containing electrolyte. The co-doping of transition metal ion and Gd3+ in ceria is an available new method to reduce the densification temperature, while have a negative effect on the electrical performance. Herein, a strategy of micro-doping for bifunctional Ce0.9Gd0.09M0.01O2−δ (M = Fe, Cu) interlayers is proposed to achieve excellent sintering performance and electrochemical performance. The results indicate that adequate liquid phase production and lattice doping could simultaneously increase the relative density at lower sintering temperature and improving the electrical conductivity of interlayers. 1 mol.% Cu micro-doping could reduce the sintering temperature by 350 °C, make the relative density up to be 96.26%, and the electrical conductivity of 600 °C up to be 0.0134 S/cm. The single cell with Ce0.9Gd0.09Cu0.01O2−δ (GCDC) interlayer has the low ohmic resistance of 0.31 Ω cm2, and exhibits a high maximum power density of 0.745 W cm−2 at 750 °C, which was higher than 0.603 W cm−2 of the single cell with undoped GDC interlayer.

Experimental study on flow boiling-based micro-channel configurations for the PEMFC cooling

Proton Exchange Membrane Fuel Cell (PEMFC) is one of the most promising energy conversion devices. Efficient thermal management is crucial for maintaining the PEMFC's efficiency and durability. However, cooling the PEMFC can be challenging due to the small temperature differences between the stack's operating temperature and the surrounding environment. In the present study, flow boiling is applied as a cooling technique for the PEMFC. A flow boiling experimental test bench with fluid flow visualization is built for PEMFC cooling. To relieve the negative effect of mal-distribution of working fluid in the micro-channels, the cooling configurations with orifice baffles are also tested. Flow boiling performance of HFE-7100 in the micro-channel-based cooling configuration for PEMFC is experimentally investigated. The flow boiling characteristics of HFE-7100 in the micro-channel are revealed, which is beneficial for the appropriate design of flow boiling-based cooling configuration for the PEMFC. Excellent temperature distribution uniformity of flow boiling-based cooling PEMFC is achieved and is further enhanced by adding orifice baffles.

Multi-band tunable strongly nonreciprocal thermal radiation in topological edge state coupled mode

Violating Kirchhoff's law of thermal radiation can break the reciprocity constraints on spectral emissivity and absorptivity, which provides new capabilities for managing photonic heat flow and fundamentally improves energy harvesting systems' efficiency. Currently, most micro-nano structures that violate Kirchhoff's law are mainly confined to single- or dual-band models, significantly limiting applications such as photonic energy conversion and thermal management. Here, a scheme is proposed for a topological one-dimensional photonic crystal heterostructure consisting of multiple photonic crystals and Weyl semimetals, and its absorptivity and emissivity are theoretically calculated by the transfer matrix method. The results show that the multi-band nonreciprocity that completely violates Kirchhoff's law can persist over broad angular and frequency ranges without requiring any external magnetic field via tuning the relevant parameters. Furthermore, the electric field distribution reveals that the formation of such multiple bands originates from the coupling between topological edge states, and the significant enhancement of the local field near the interface of the heterostructure provides favorable conditions for the realization of strong nonreciprocity. Our work may contribute to the design and development of multiband nonreciprocal devices for energy conversion and thermal management and may also provide design ideas for multiband reciprocal absorbers, filters, optical switching, etc.