The transition to renewable energy systems requires sustainable, high-performance energy storage materials. Here, we report a simple and scalable layer-by-layer assembly strategy to fabricate hybrid supercapacitor electrodes composed of lignin, multi-walled carbon nanotubes (MWCNTs), and Mn2C MXene, followed by controlled carbonization. Lignin, an abundant and renewable by-product of the pulp and paper industry, serves as a lowcost carbon precursor, enabling a circular and sustainable approach to electrode design. Carbonization at 900 K converts lignin into a conductive, graphitized carbon matrix while maintaining MXene's electrochemical functionality, resulting in a hierarchical architecture that suppresses MXene restacking and facilitates rapid ion and electron transport. The optimized electrode delivers a high specific capacitance of 186.7 F g- 1, representing a more than seven-fold improvement compared with non-carbonized electrodes, along with an energy density of 6.48 Wh kg- 1 at a power density of 2.33 kW kg-1. Excellent cycling stability is achieved, with 87.7% capacitance retention after 1000 charge-discharge cycles. These results demonstrate the potential of lignin-derived MXene composites as sustainable and high-performance electrode materials for advanced supercapacitors, supporting the development of affordable and clean energy storage technologies in alignment with United Nations Sustainable Development Goal 7.

Amine-functionalized lignin hydrogels serve as stable n-type thermoelectric materials through the thermodiffusion effect, offering efficient energy harvesting platforms.

This study investigates polycrystalline NaxCoO2 thin films synthesized via spray pyrolysis on glass substrates over a wide compositional range of x. The films were grown using cobalt acetate tetrahydrate and sodium hydroxide as precursors, employing different precursor solution molarities to control the growth dynamics. The characterization of the system was conducted using X-ray Diffraction, Scanning Electron Microscopy, Optical Transmittance, and Raman spectroscopy. Raman spectroscopy revealed oxygen in-plane motion modes under specific excitation wavelengths due to optical resonance conditions and identified the films as gamma-NaxCoO2. The growth of gamma-NaxCoO2 phase is favored by a high-molarity synthesis mode followed by an oxygen thermal annealing. At room temperature, films with higher sodium content exhibited decreased Seebeck coefficients and electrical resistivity. Notably, a maximum power factor of approximately similar to 3.3 mu W/K(2)m was achieved at x = 0.93. Conversely, films prepared at low-molarities presents Na-content Co3O4 phases and Seebeck coefficients up to 500 mu V/K yet suffer from poor electrical conductivity. These findings underscore the viability of spray pyrolysis as a scalable method for producing p-type thermoelectric layers such as NaCoO2.

Thermoelectric materials are attracting attention for their ability to convert heat into electricity, traditionally assessed through a figure of merit (ZT) depending on the electrical conductivity, Seebeck coefficient, and thermal conductivity. Developing efficient ionic thermoelectric materials presents challenges as they cannot integrate directly into standard generators. However, they can utilize the ionic thermoelectric effect to charge supercapacitors. This study investigates lignin, an abundant plant-based waste, as a basis for ionic thermoelectric systems, combining sustainability and thermoelectric efficiently. Lignin-based hydrogels with varying compositions were examined for their thermoelectric properties, revealing gigantic ionic Seebeck coefficients of up to 30.4 mV K-1 and good conductivity, reaching 5.87 S m-1. The optimal hydrogel composition displayed a high-power factor of 4187 μW m-1 K-2, and an impressive ionic iZT value of 3.5, showcasing the potential of lignin-based hydrogels for ionic thermoelectric systems. This research suggests a promising avenue for addressing environmental and economic challenges in energy production.

Tailoring magnetoresistance and magnetic anisotropy in van der Waals magnetic materials is essential for advancing their integration into technological applications. In this regard, strain engineering has emerged as a powerful and versatile strategy to control magnetism at the 2D limit. Here, it is demonstrated that compressive biaxial strain significantly enhances the magnetoresistance and magnetic anisotropy of few-layer CrSBr flakes. Strain is efficiently transferred to the flakes from the thermal compression of a polymeric substrate upon cooling, as confirmed by temperature-dependent Raman spectroscopy. This strain induces a remarkable increase in the magnetoresistance ratio and in the saturation fields required to align the magnetization of CrSBr along each of its three crystalographic directions, reaching a twofold enhancement along the magnetic easy axis. This enhancement is accompanied by a subtle reduction of the Néel temperature by ≈10 K. The experimental results are fully supported by first-principles calculations, which link the observed effects to a strain-driven modification in interlayer exchange coupling and magnetic anisotropy energy. These findings establish strain engineering as a key tool for fine-tuning magnetotransport properties in 2D magnetic semiconductors, paving the way for implementation in spintronics and information storage devices.

Narrow and brilliant spectral lines are essential assets for high-resolution spectroscopy as well as for precision sensing and optomechanics. In semiconductor structures and, in particular, in the well-established (Al,Ga)As material system, strong emission lines with nanosecond coherence times can be provided by the opto-electronic resonances of microcavity exciton-polariton condensates. The temporal coherence of these resonances, however, normally rapidly deteriorates as the temperature increases beyond a few tens of kelvins due to exciton dissociation. Here, we demonstrate that the temperature stability of polariton condensates in (Al,Ga)As can be significantly improved by confinement within micrometer-sized intracavity traps. We show that trapped condensates can survive up to 200 K while maintaining a light-matter character with decoherence rates below 10 GHz (i.e., < 40 μeV linewidths). These linewidths are by an order of magnitude smaller than those so far reported for other solid-state systems at these temperatures. Confinement thus provides a pathway towards room-temperature polariton condensation using the well-established (Al,Ga)As material system with prospects for application in scalable on-chip photonic devices for optical processing, sensing, and computing.

Improving light absorption is essential for the development of solar thermoelectric generators. Most efficient light absorbers require a back mirror (a thick metal film) to reduce the reflectivity by promoting the interference between the incident and the reflected light. However, the presence of thick a continuous metal film supposes a limitation for thermoelectric applications, as it behaves like a shortcut of the Seebeck voltage. In this work, a back mirror-free selective light absorber is presented, designed for the fabrication of thermoelectric devices. The combination of a high and a low refractive index material covered by a semi-transparent electrode is optimized. As a difference to the back mirror, the semi-transparent electrode can be patterned to prevent the quenching of the Seebeck voltage. Thanks to this, the low refractive index material can be replaced by a transparent thermoelectric, enabling efficient heat-to-energy conversion with negligible loss of absorption performance.

Plasmonic heating in geometrically optimized bismuth telluride (Bi2Te3) nanostructures enables efficient thermoelectric energy harvesting by reducing interfacial losses compared to metal nanoparticle-dependent systems. We demonstrate that 3D Bi2Te3 nanowire networks, fabricated via template-assisted electrochemical deposition, achieve a localized temperature rise of 14 degrees C under 650 nm illumination, which is twice the heating obtained in 1D nanowire arrays and three times higher than Bi2Te3 films, through intrinsic plasmonic resonance. Raman thermometry and wavelength-dependent analysis reveal that this geometric enhancement correlates with a 250 % increase in thermoelectric voltage output compared to conventional designs. By leveraging Bi2Te3's dual functionality as a topological insulator and plasmonic material, our work establishes a scalable, cost-effective platform for advanced energy harvesting devices, with immediate applications in wearable IoT systems and sustainable thermal management technologies.

Wood-based ionic conductive membranes have emerged as a new paradigm for low-grade thermal energy harvesting applications due to their unique andtailorable structures. Herein, a lignin-derivedionic conducting membrane with hierarchical aligned channels is synthesized viaa double network crosslinking approach. Their excellent thermal stability andsuperior swelling ratio allow their optimization as low-grade heat recovery technologies. Several vertically aligned nanoscaleconfinements are found in the synthesized membranes, contributing towardenhanced ionic diffusion. Among all the combinations, the membrane comprising69.2 wt.% of lignin and infiltrated with 0.5 m KOH exhibits anexceptional ionic figure of merit (ZTi) of 0.25, relatively higher ionic conductivity(51.5 mS cm-1), lower thermal conductivity(0.195 W m-1 center dot K), and a remarkable ionic Seebeck coefficientof 5.71 mV K-1 under the application of an axialtemperature gradient. A numerical model is also utilized to evaluate theveracity of experimental observations and to gain a better understanding of thefundamental mechanisms involved in attaining such values. These results displaythe potential of lignin-basedmembranes for future thermal energy harvesting applications and are a new facetin thermoelectric energy conversion which is certain to pave the way forfurther investigations on sustainable ionic conductive membranes. Lignin-based ionic thermoelectric membranes with hierarchically aligned channels are synthesized for efficient low-grade thermal energy harvesting. These membranes showcase exceptional ionic conductivity, thermopower, thermal stability, and unique properties, achieving an impressive ionic figure of merit of 0.25, setting a new standard in sustainable thermoelectric energy conversion. These findings unveil promising potential for sustainable ionic conductive membranes in thermal energy harvesting.image

The development of wearable thermoelectric generators (wTEG) represents a promising strategy to replace batteries and supercapacitors required to supply electrical energy for portable electronic devices. However, the main drawback of wTEGs is that the thermal gradient between the skin and the ambient is minimal, reducing the power output produced by the generator. Therefore, it is necessary to improve the thermal management of wTEG in order to increase its efficiency. This work deals with the preparation of a thermoelectric generator that harnesses the plasmonic heating effect to enhance the thermal gradient of the final device. The thermoelectric layer is created through the in situ polymerization of terthiophene (3T) within a polyurethane matrix, utilizing silver (Ag) (I) and copper (II) perchlorate as oxidants. The plasmonic film, composed of Ag-NP (nanoparticles), is formed via photocatalytic reduction of silver nitrate in the presence of titanium oxide. These layers are then meticulously assembled to yield the hybrid plasmonic/thermoelectric generator. Plasmonic materials such as silver nanoparticles represent an excellent alternative to improve the thermal management of wearable thermoelectric generators (wTEG). Through the absorption of solar light, plasmonic materials can convert it into heat and maximize the thermal gradient of the wTEG, and therefore increasing the power output delivered by the wTEG. image

Abstract In this work, ultrathin nickel films are developed for application as transparent electrodes in thermoelectric devices. The quality of the films is determined systematically by electrical, optical, and morphological characterization in a series of samples with different thickness. The thermal properties of the films show a dramatic dependence of the Seebeck coefficient on the film thickness. This dependence, with values ranging from −16 to +5 𝜇V K−1 for thicknesses from 10 to 2 nm, includes a change in the behavior of the thermoelectric response from n‐ to p‐type. It has also been demonstrated that the accurate estimation of the thermal conductivity in thin films is challenging due to substrate effects. In this situation, a differential measurement method based on scanning thermal microscopy is proposed, as in these conditions the measurements are less sensitive to the substrate effects. In further works, the dependence of the thermal properties of ultrathin nickel films can be exploited as a tuning parameter for the design of thermoelectric devices.

In this study, we have improved the power factor of conductive polymer nanocomposites by combining layer-by-layer assembly with electrochemical deposition to produce flexible thermoelectric materials based on PEDOT/carbon nanotubes (CNTs)—films. To produce films based on CNTs and PEDOT, a dual approach has been employed: (i) the layer-by-layer method has been utilized for constructing the CNTs layer and (ii) electrochemical polymerization has been used in the synthesis of the conducting polymer. Moreover, the thermoelectric properties were optimized by controlling the experimental conditions including the number of deposition cycles and electropolymerizing time. The electrical characterization of the samples was carried out by measuring the Seebeck voltage produced under a small temperature difference and by measuring the electrical conductivity using the four-point probe method. The resulting values of the Seebeck coefficient S and σ were used to determine the power factor. The structural and morphological analyses of CNTs/PEDOT samples were carried out using scanning electron microscopy (SEM) and Raman spectroscopy. The best power factor achieved was 131.1 (μWm−1K−2), a competitive value comparable to some inorganic thermoelectric materials. Since the synthesis of the CNT/PEDOT layers is rather simple and the ingredients used are relatively inexpensive and environmentally friendly, the proposed nanocomposites are a very interesting approach as an application for recycling heat waste.

Converting waste heat from solar radiation and industrial processes into useable electricity remains a challenge due to limitations of traditional thermoelectrics. Ionic thermoelectric (i-TE) materials offer a compelling alternative to traditional thermoelectrics due to their excellent ionic thermopower, low thermal conductivity, and abundant material options. This review categorizes i-TE materials into thermally diffusive and thermogalvanic types, with an emphasis on the former due to its superior thermopower. This review also highlights the i-TE materials for creating ionic thermoelectric supercapacitors (ITESCs) that can generate significantly higher voltages from low-grade heat sources compared to conventional technologies. Additionally, it explores thermogalvanic cells and combined devices, discussing key optimization parameters and theoretical modeling approaches for maximizing material and device performance. Future directions aim to enhance i-TE material performance and address low energy density challenges for flexible and wearable applications. Herein, the cutting-edge of i-TE materials are comprehensively outlined, empowering researchers to develop next-generation waste heat harvesting technologies for a more sustainable future.

The efficient and economical conversion of low-grade waste heat into electricity has promising potential to combat the greenhouse effect and expedite the shift towards sustainable development. This study presents an innovative and appealing approach through the utilization of lignin, an abundant waste product derived from the paper and pulp industry, to develop hydrogels as compelling and sustainable materials for application in ionic thermoelectricity. Various compositions were evaluated to examine the impacts of varying lignin concentrations, types of electrolytes, concentrations of crosslinkers, and electrolyte concentrations on the ionic thermoelectric performance of the hydrogels. The optimized lignin-derived hydrogel, infiltrated with a 6 M KOH electrolyte, demonstrates high ionic conductivity (226.5 mS/cm) and a superior Seebeck coefficient of 13 mV/K. This results in a remarkable power factor (3831 µW/m·K 2 ) that leads to an impressive Figure of merit (ZT i ) (3.75), surpassing most of the existing state-of-the-art materials and making it the most efficient sustainable ionic thermoelectric material reported until now. These findings underscore the exceptional performance of lignin-based hydrogels in the realm of low-grade waste energy harvesting applications. The present study contributes to address the challenges posed by waste heat through effectively harnessing low-grade waste heat through the utilization of sustainable lignin-based hydrogels while reducing the reliance on fossil fuels and minimizing greenhouse gas emissions. Graphical Abstract

Magnetic 2D materials hold promise to change the miniaturization paradigm of unidirectional photonic components. However, the integration of these materials in devices hinges on the accurate determination of the optical properties down to the monolayer limit, which is still missing. By using hyperspectral wide-field imaging at room temperature, we reveal a nonmonotonic thickness dependence of the complex optical dielectric function in the archetypal magnetic 2D material CrI_{3} extending across different length scales: onsetting at the mesoscale, peaking at the nanoscale, and decreasing again down to the single layer. These results portray a modification of the electronic properties of the material and align with the layer-dependent magnetism in CrI_{3}, shedding light on the long-standing structural conundrum in this material. The unique modulation of the complex dielectric function from the monolayer up to more than 100 layers will be instrumental for understanding mesoscopic effects in layered materials and tuning light-matter interactions in magnetic 2D materials.

The recent development in the field of wearable electronics has increased the demand for batteries as power sources which are subjected to periodic recharging and replacement. Therefore, the next challenge is to design new systems for sustainable energy to power portable electronic devices that can be easily integrated into textiles such as thermoelectric generators that can convert waste heat into electricity. Looking at this scenario, this work shows a methodology to prepare thermoelectric textiles by electrochemical polymerization of poly(3,4‐ethylenedioxythiophene) (PEDOT) on felt fabrics. The polymerization of PEDOT is carried out utilizing three different counterions, LiClO 4 , 1‐butyl‐3‐methylimidazolium hexafluorophosphate (PF 6 ), and 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (BTFMSI) to provide a complete understanding of the role of the counterion in the thermoelectric properties. The electrical conductivity and Seebeck coefficient are dependent on the counterion, reaching the maximum ZT for PEDOT polymerized in presence of BTFMSI due to an improvement of carrier mobility. In addition, the manufactured textile thermoelectric device showed an outstanding power output (6.5 µW) compared to the previous devices reported to date.

Peripheral nerve injury (PNI) often clinically relies on the use of nerve grafts taken from the patient to establish a therapeutic effect, though secondary site of injury and morbidity have prompted the medical community to find alternative solutions. A new trend in the development of biomaterials arises in the form of electro-conductive biomaterials, especially for electrically active tissues such as the peripheral nerves. In this work, novel poly(3,4-ethylenedioxythiophene) PEDOT nanoparticles (PEDOT NPs) were synthetized via the mini-emulsion method and were combined with silk fibroin (SF) to create conduits for PNI repair. The synthesized PEDOT NPs-loaded SF conduits showed optimal properties for peripheral nerve substitution from the physico-chemical and biological point of view. They displayed excellent mechanical and conductivity performance with the tensile moduli reaching 6.61 ± 0.55 MPa and the conduits reaching 5.4 · 10 –4 S cm −1 , respectively. The conduits did not possess apatite-forming capacity, which were resistant to bending occlusions for angles up to 50° and to suturing. The developed conduits are promising as a novel biomaterial for applications in peripheral nerve regeneration; in vitro experiments showed that they did not allow BJ fibroblast infiltration, avoiding scar tissue formation in the lumen, and they did not show any toxic effect for Schwann cells.

We present a comprehensive study on the structure and optical properties of Mn-and Co-doped ZnO samples prepared via solid-state reaction method with different dopant concentrations and atmospheres. The samples were structural and chemically characterized via X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray excited photoelectron spectroscopy. The optical characterization was performed via Raman, photoluminescence, and diffuse photoreflectance spectroscopies. Emphasis was done on the studies of their vibrational properties. The structural data confirm the incorporation of Mn and Co ions into the wurtzite ZnO lattice. It is demonstrated that the usual observed additional bands in the Raman spectrum of transitional metal (TM) doped ZnO are related to structural damage, deriving from the doping process, and surface effects. The promoted surface optical phonons (SOP) are of Fröhlich character and, together with the longitudinal optical (LO) polar phonons, are directly dependent on the ZnO electronic structure. The enhancement of SOP and LO modes with TM-doping is explained in terms of nonhomogeneous doping, with the dopants concentrating mainly on the surface of grains, and a resonance effect due to the decrease of the ZnO bandgap promoted by the introduction of the 3d TM levels within the ZnO bandgap. We also discuss the origin of the controversial vibrational mode commonly observed in the Mn-doped ZnO system. It is stated that the observation of the analyzed vibrational properties is a signature of substitutional doping of the ZnO structure with tuning of ZnO optical absorption into the visible range of the electromagnetic spectrum.

The development of wearable technology has promoted the research of new power supply sources to feed wearable devices without the need of batteries. Wearable thermoelectric generators (wTEGs) can generate energy using the thermal gradient between the human body and the ambient temperature. The most comfortable way to adapt wTEGs to the human body is by using textiles, which are flexible and breathable. In this work, we have developed a method to coat textiles with conductive polymers by electrodeposition on fabrics previously coated with multi-walled carbon nanotubes (MWCNT). The results show that the fabrics coated with polyaniline: sulfuric acid (PANI:H2SO4) present a very low thermal stability, and the variation of the electrical conductivity under wearable stress is not suitable for their use in smart textiles. However, the fabrics coated with poly (3,4-ethylenedioxythiophene: perchlorate) (PEDOT:ClO4) and polypyrrole: perchlorate (PPy:ClO4) show a good thermal stability, positive evolution of the electrical conductivity as a function of the twist angle, bending cycles, and bending radius, demostrating their potential use in practical wearable applications to coat fabrics by electrochemical deposition.

Thermoelectric (TE) materials can have a strong benefit to harvest thermal energy if they can be applied to large areas without losing their performance over time. One way of achieving large-area films is through hybrid materials, where a blend of TE materials with polymers can be applied as coating. Here, we present the development of all solution-processed TE ink and hybrid films with varying contents of TE Sb2Te3 and Bi2Te3 nanomaterials, along with their characterization. Using (1-methoxy-2-propyl) acetate (MPA) as the solvent and poly (methyl methacrylate) as the durable polymer, large-area homogeneous hybrid TE films have been fabricated. The conductivity and TE power factor improve with nanoparticle volume fraction, peaking around 60-70% solid material fill factor. For larger fill factors, the conductivity drops, possibly because of an increase in the interface resistance through interface defects and reduced connectivity between the platelets in the medium. The use of dodecanethiol (DDT) as an additive in the ink formulation enabled an improvement in the electrical conductivity through modification of interfaces and the compactness of the resultant films, leading to a 4-5 times increase in the power factor for both p- and n-type hybrid TE films, respectively. The observed trends were captured by combining percolation theory with analytical resistive theory, with the above assumption of increasing interface resistance and connectivity with polymer volume reduction. The results obtained on these hybrid films open a new low-cost route to produce and implement TE coatings on a large scale, which can be ideal for driving flexible, large-area energy scavenging technologies such as personal medical devices and the IoT.