Superconcentrated electrolytes (e.g., water-in-salt electrolytes) exhibit large electroneutral and non-electroneutral aggregates/networks (similar to 1-5 nm). Depending upon the surface charge density and the pore size of nanoporous separators and electrodes, the electrolyte residing within similar to 1-10 nm sized pores may contain either (i) a single cation- or anion-dominated network, or (ii) multiple alternating layers of cation- or anion-dominated networks. Scenario (i) is similar to overlapping condensed double layers in smaller pores with high surface charge densities. Non-electroneutrality within a pore in both scenarios brings electrokinetics into play, which is not accounted for in the standard pseudo-2D (P2D) model. Based on statistical mechanics and electrochemistry, we present a new model for 'superconcentrated electrolytes interacting with nanoporous materials' that incorporates electrokinetic effects, predicts that the transference number is no longer solely an electrolyte property, but depends on the separator morphology and electrolyte volume. We also present experimental evidence supporting our model's prediction of electrokinetically driven current oscillations in chronoamperometry. Our proposed model has applications across multiple domains where superconcentrated electrolytes are used in combination with nanoporous materials. Our results indicate that using superconcentrated electrolytes with nanoporous materials is another method for developing flowing electrolyte metal batteries - an emerging class of batteries - in commercial form factors (e.g., coin and pouch cells).

The electrolyte flow in a battery can enhance its performance by mitigating dendrite formation and fostering the growth of a stable, uniform solid electrolyte interphase (SEI). Here, we illustrate a mechanism for introducing electrolyte flow within batteries of commercially viable architectures, such as coin, pouch, and cylindrical cells. In our lithium-ion coin cells using 1 M LiPF6 in EC:DEC (1:1 by vol), chronoamperometry step of the Bruce-Vincent method for measuring the transference number, we observed an unexpected, separator-dependent current increase. While Bruce-Vincent method assumes only Fick’s diffusion and ionic migration as the ion transport mechanisms, our results point to an additional mechanism – ‘separator polymer strand dynamics (SPSD)-driven electrolyte advection.’ This indicates that a new physically relevant parameter that includes electrolyte advection effects is needed for accurate determination of the transference number. We further demonstrate, for the first time, that polymer strand dynamics also lead to peaks and valleys in capacity as a function of cycle number in half-cells. Notably, we also elaborate future research opportunities arising out of these findings which include, (i) focusing on SPSD for a better battery performance, (ii) carefully designing fast charging protocols that account for the unexpected current increase during the constant voltage step, (iii) studying oscillations in batteries and other devices to develop physics-based digital twins, (iv) developing a new battery performance parameter that accounts for electrolyte advection, and (v) leveraging electrolyte flow to eliminate dendrite growth in metal anode batteries without changing cell form factors, using external pumping systems, and additional accessories.

Harvesting ubiquitous low-grade waste heat has remained challenging, and ionic thermoelectrics (i-TEs) have shown greater promise than electronic thermoelectrics. The i-TEs are of two types: (1) redox reaction-based i-TEs and (2) Soret effect-driven i-TEs. This work summarizes recent advances in Soret effect-driven i-TEs, which generate a voltage due to differences in the thermophoretic mobilities of electrolyte ions when the i-TE is subjected to a temperature gradient, with the cold end at room temperature. Unlike electronic thermoelectrics, Soret effect-driven i-TEs exhibit a high thermopower of several mV/K. We correlate the thermopower generated by such Soret effect-driven i-TEs to (1) the various entropic contributions of the electrolyte, and (2) electrode porosity. We highlight the role of electrode porosity in driving novel electrochemical voltage oscillations, which can open new avenues for i-TE applications. Notably, we present proof-of-concept demonstrations of Soret effect-driven i-TEs and discuss various schemes employed by researchers to continuously generate power—a hot discussion topic in the field of i-TEs. Lastly, we compare the efficiencies of reported i-TEs and propose future directions to guide the research community in Soret effect-driven i-TEs. In this invited review article, we summarize the (1) developments in electrolyte discovery for Soret effect-driven i-TEs and link them to their entropic contributions, (2) role of electrode porosity in governing thermopower and voltage oscillations, (3) different continuous operation schemes, (4) proof-of-concept demonstrations reported to date, and (5) future research directions.

Developing bone replacement scaffolds has been a driving ambition of regenerative medicine. Although great progress has been achieved for small scaffolds, the real clinical need is for large scaffolds >5 mm. Oxygenating these scaffolds is challenging, as slow diffusion rates lead to necrotic regions in the scaffold core. In this work, we modulate in vitro oxygen concentration in a scaffold in a flow chamber using an external perfusion pump while imaging oxygen concentrations below the scaffolds. With no external flow, yeast cells growing in the scaffold deplete oxygen, especially from the center, with concentrations reaching a steady state consistent with reaction-diffusion models. The oxygen is restored via pumping fresh medium through the scaffold. The oxygen profiles are highly reproducible from cycle to cycle. This lays the groundwork for future in vivo oxygen imaging studies using localized light sources and external perfusion pumps for modulation.

We present Soret effect-driven electrochemical devices that generate >1 V with a mere 10 K temperature difference with the cold end at room temperature, i.e., a thermopower alpha > 100 mV K-1 - almost four to five times the record to date [Adv. Energy Mater., 2019, 9, 1901085]. We show that alpha depends not only on the electrolyte composition but also on the electrode porosity and microstructure, which has remained an understudied area of research. Interestingly, our devices show novel voltage oscillations (unlike electrochemical oscillations observed previously, which were a result of either (a) stochastic single-molecule electrochemistry or (b) redox reactions) arising from an interplay between ionic diffusion and ionic migration within the electric double-layer, highlighting the potential for novel applications. Notably, the real-world use of TRECO is demonstrated by (a) facile continuous operation, (b) harvesting body heat (similar to 825 mV obtained for a temperature difference of 6 K), and (c) powering a pocket calculator using a single large format TRECO cell to harvest waste heat from warm continuously operating lab equipment.

Correction for ‘An electrochemical oscillator for harvesting near room temperature waste heat’ by Basanta Ghimire et al. , J. Mater. Chem. A , 2025, 13 , 6560–6572, https://doi.org/10.1039/D4TA08559K.

The demand for wearable medical devices among older adults, particularly those with cognitive decline, is growing. Developing self-powered wearables that eliminate the need for battery recharging or replacement will significantly enhance user-friendliness for individuals with cognitive decline, who may forget to maintain their devices. Constant, passive power from natural sources may be key to unlocking wearables’ potential. The heat produced by human bodies, as a natural and sustainable energy source, is a prime candidate for this task. The use of thermoelectric generators (TEGs) for harvesting high-grade heat has been extensively studied over time. However, capturing ubiquitous low-grade heat near room temperature (e.g., body heat) remains a significant challenge. We developed a thermally rechargeable electrochemical oscillator (TRECO) that harvests ultralow-grade heat for powering small devices. Specifically, an ionic thermoelectric cell composed of two porous electrodes and a cellulosic separator was assembled and evaluated. The voltage generation near room temperature based on the Soret effect was studied for several porous electrodes. The armband with a single TRECO cell generated approximately 825 mV from a small temperature difference of 6 K, with human skin as the hot end and the surrounding environment as the cold end. This results in a more than 130 mV K -1 thermopower, almost four to five times the record to date. It was found that the electrolyte composition and the electrode porosity and microstructure can influence the device's thermopower. The developed device can be charged by maintaining a low-temperature difference across its two electrodes. A novel ionic thermoelectric device was developed to harvest ultralow-grade heat from the body for power generation effectively. This technology holds great potential for powering wearable health monitoring devices for older adults with cognitive decline, as it can overcome challenges associated with their cognitive impairment, which may hinder their ability to recharge their devices.

Harvesting high-grade waste heat using thermoelectric generators based on the Seebeck effect has been explored for a while, but harvesting the ubiquitous near-room temperature waste heat (e.g., waste heat from hot mobile phones, laptops, body heat, etc.) has remained a challenge. In this work, we present Soret effect-driven thermally rechargeable electrochemical oscillators (TRECO) that generate >1 V with a mere 10 K temperature difference with the cold end at room temperature, i.e., a thermopower α > 100 mV/K. This is four to five times the record thermopower reported to date [Adv. Energy Mater., 2019, 9 , 1901085]. Our focus on electrode porosity and microstructure (along with electrolyte composition), which is an understudied area of research, helped us achieve such a high thermopower. Interestingly, TRECO exhibits novel voltage oscillations unlike previously reported electrochemical oscillations, which resulted from either (a) stochastic single-molecule electrochemistry or (b) redox reactions. Through analytical models and carefully designed experiments, we showed that the oscillations arise from an interplay between ionic diffusion and ionic migration within the electric double-layer. Additionally, we also proposed a facile continuous operation scheme for TRECO, which enables real world operation. Notably, we also demonstrated TRECO's ability to operate in real time by (a) harvesting body heat (∼825 mV obtained for a temperature difference of 6 K), and (b) powering a pocket calculator using a single large format TRECO cell to harvest waste heat from warm continuously operating lab equipment. Ref: Ghimire, Basanta, Mihir Parekh, Herbert Behlow, Morteza Sabet, Sriparna Bhattacharya, Nawraj Sapkota, Pankaj Singh Chauhan, Abha Misra, and Apparao M. Rao. "An electrochemical oscillator for harvesting near room temperature waste heat." Journal of Materials Chemistry A (2025). Figure 1

Famatinite (Cu3SbS4) is an earth-abundant, nontoxic material with potential for thermoelectric energy generation applications. Herein, rapid, energy-efficient, and facile one-pot modified polyol synthesis was utilized to produce gram-scale quantities of phase-pure famatinite (Cu2.7M0.3SbS4, M = Cu, Zn, Mn) nanoparticles (diameter 20–30 nm) with controllable and stoichiometric incorporation of transition metal dopants on the Cu-site. To produce pellets for thermoelectric characterization, the densification process by spark plasma sintering was optimized for individual samples based on thermal stability determined using differential scanning calorimetry and thermogravimetric analysis. Electronic transport properties of undoped and doped famatinite nanoparticles were studied from 225–575 K, and the thermoelectric power factor was calculated. This is the first time electronic transport properties of famatinite doped with Zn or Mn have been studied. All famatinite samples had similar resistivities (>0.8 mΩ·m) in the measured temperature range. However, the Mn-doped famatinite nanomaterials exhibited a thermoelectric power factor of 10.3 mW·m−1·K−1 at 575 K, which represented a significant increase relative to the undoped nanomaterials and Zn-doped nanomaterials engendered by an elevated Seebeck coefficient of ~220 µV·K−1 at 575 K. Future investigations into optimizing the thermoelectric properties of Mn-doped famatinite nanomaterials are promising avenues of research for producing low-cost, environmentally friendly, high-performing thermoelectric materials.

X-ray excited luminescence chemical imaging (XELCI) and associated sensor surfaces are designed to noninvasively study, detect, and monitor local chemistry at the surface of modified implanted medical devices during infection. Implants are coated with polymer films containing scintillators and pH indicator dyes that together generate a pH-dependent luminescence when irradiated by X-rays. A focused X-ray beam provides high spatial resolution, while the pH indicator provides chemical sensitivity. A live rabbit pH-imaging study on a scintillator-coated implanted titanium plate evaluates the sensor performance with and without Staphylococcus aureus infection and biocompatibility through long-term histological examinations. 5000 cfu are sufficient to cause infection without fatality. XELCI images clearly shows dye and reference regions in live rabbits; no leaching is evident in titanium plates coated with polyethylene glycol (PEG) hydrogel up to 10 days, although dye leached fromvinyl-PEG film-coated implants. No toxicity is evident, and pH sensors remained stable after up to 3 months postimplantation. In these preliminary studies, acidosis is not observed in either infected or control legs in vivo or postmortem. The results demonstrate the feasibility of imaging pH and provide insights for optimizing the sensor and the imaging modality for subsequent studies on pH changes on implants during infection.

AbstractA new hybrid ultrasound luminescent chemical imaging technique is described along with a pH sensor to image chemical concentrations at the surface of implanted medical devices. The purpose is to detect and study local biochemistry during infection. The sensor comprises a mechanoluminescent film (SrAl2O4:Eu, Dy microphosphors embedded in a biocompatible polymer film) and a pH indicator dye. A focused ultrasound beam generates green luminescence at the ultrasound focal point. By pulsing the ultrasound ON and OFF, the modulated luminescence can be distinguished from persistent luminescence, for high spatial resolution imaging. A red fluorescent dye and the pH indicator dye bromothymol blue are added to the coating to modulate the red‐light transmittance via pH dependent absorbance. Acidosis is observed as an increase in red luminescence intensity in spectroscopy and imaging. The films are sensitive to biologically relevant changes in pH (6.0–8.0) and can be imaged through optically scattering media to mimic tissue. The images have a knife edge spatial resolution of ≈3 mm through optically scattering phantoms, limited by the focused ultrasound spot size. This novel technique may permit the elucidation of implant infection at the implant surface and can be further developed for the measurement of other relevant chemical species in the future.

Phonons and related processes govern the thermal properties of materials. They can be excited externally using light, heat, mechanical energy, etc. This article aims to elucidate the methodology used in studying thermal properties, specifically employing temperature-dependent Raman spectroscopy. However, unique challenges arise when applying these techniques to low-dimensional materials. We summarize theoretical and experimental studies highlighting the significance of phonon hydrodynamics—a phenomenon typically observed only at low temperatures in bulk materials, but now found at room temperature in 2D materials like graphene. This discovery calls for caution when utilizing temperature-dependent Raman spectroscopy-based techniques, such as the optothermal Raman method, which has been extensively employed to experimentally determine the thermal conductivity of graphene. Moreover, temperature-dependent Raman spectroscopy remains a valuable tool for investigating phonon anharmonicity, a key factor governing phonon transport and decay processes in a wide array of emerging 2D materials and their heterostructures.

Oxygenation concentration of tissue is an important factor in culturing stem cells and in studying the therapy response of cancer cells. The hypoxia bone marrow is the site to harbor cancer cells. Thus, direct high-resolution measurements of molecular O2 would provide powerful means of monitoring cultured stem cells and therapied cancer cells. We proposed an imaging approach to measure oxygenation concentration in deep tissues, based on the XLCT, with combined strengths of high chemical sensitivity and high spatial resolution. We have developed different biosensing films for oxygenation measurements and tested these films with X-ray luminescent experiments. We have also performed phantom experiments with multiple targets to validate the XLCT imaging system with measurements at two channels.

We use Peltier cooling to experimentally determine the thermoelectric figure-of-merit of a material, where the maximum temperature depression, ΔTmax, is simply related to Z of a thermocouple. However, for thermocouples comprising good thermoelectric materials with ZT≥1, ΔTmax can be large (≥100 K), making it difficult to assign the measurement to a particular temperature. This is less of a problem if the thermocouple consists of a semiconductor and a metal since ZT and ΔTmax are then much smaller. We developed a procedure for measuring the dimensionless figure-of-merit of a semiconductor using semiconductor-metal thermocouples in which the form factor (i.e., the ratio of areas to lengths of the two branches) is optimized. We also show valuable aspects in the ΔTmax measurement when the material dimensions are varied. Our experiments on couples consisting of a bismuth telluride alloy and constantan, and the corresponding theoretical analysis, show that the radiation losses are significant at ordinary temperatures. A good estimate of thermal conductivity and zT of the sample can be obtained when radiation losses are minimized.

Solid-state thermoelectrics have focused on thermal to electrical energy conversion for many decades. Nevertheless, the thermoelectric energy conversion efficiency is limited by the intrinsic coupling between material properties such as electrical conductivity and the Seebeck coefficient, which reduces its efficiency despite much progress in this field. Here, we demonstrate a simple, cost-effective platform for harvesting waste heat into electricity via thermo-electrochemical cells (or thermocells) that utilize the effect of temperature on electrochemical redox potentials (i.e., the electrochemical Seebeck effect). In our preliminary experiments, coin cell type thermocells were prepared using microstructured carbon electrodes, aqueous ferricyanide/ferrocyanide redox couple, and commercial polymer separators. The wettability of the electrodes was varied by changing the duration of reactive ion etching (RIE), which improved the power performance. The highest output power (~ 75 nW) was recorded for RIE time of 3 minutes with a load of 1 kΩ. Separately, we also tested thermocells using natural wood-derived cellulose as separator materials. The performance of our thermocells will be presented, and their ability to directly power small electronic devices will be discussed.

Thermoelectric (TE) materials have received much attention due to their ability to harvest waste heat energy. TE materials must exhibit a low thermal conductivity (κ) and a high power factor (PF) for efficient conversion. Both factors define the figure of merit (ZT) of the TE material, which can be increased by suppressing κ without degrading the PF. Recently, binary chalcogenides such as SnSe, GeTe, and PbTe have emerged as attractive candidates for thermoelectric energy generation at moderately high temperatures. These materials possess simple crystal structures with low κ in their pristine forms, which can be further lowered through doping and other approaches. Here, we review the recent advances in the temperature-dependent behavior of phonons and their influence on the thermal transport properties of chalcogenide-based TE materials. Because phonon anharmonicity is one of the fundamental contributing factors for low thermal conductivity in SnSe, Sb-doped GeTe, and related chalcogenides, we discuss complementary experimental approaches such as temperature-dependent Raman spectroscopy, inelastic neutron scattering, and calorimetry to measure anharmonicity. We further show how data gathered using multiple techniques helps us understand and engineer better TE materials. Finally, we discuss the rise of machine learning-aided efforts to discover, design, and synthesize TE materials of the future.

X-ray luminescence tomography (XLT) detects X-ray scintillators contrast agents using a focused or collimated X-ray beam to provide high spatial resolution excitation through thick tissue. The approach requires bright nanophosphors that are either synthesized or purchased. However, currently available commercial nanophosphors are mostly composed of a polydisperse mixture of several micro- to nano-sized particles that are unsuitable for biomedical imaging applications because of their size and aggregated form. Here, we demonstrate a fast and robust method to obtain uniform nano to submicron phosphor particles from a commercial source of polydisperse Eu- and Tb-doped Gd2O2S particles by separating the smaller particles present using gravitational and centrifugal sedimentation. In contrast to ball milling for 15–60 min, which drastically degraded the particles’ brightness while reducing their size, our sedimentation method enabled the extraction of comparatively bright nanophosphors (≈100–300 nm in size) with a luminescence intensity of ≈10–20% of the several micron particles in the sample. Moreover, if scale up for higher yielding is required, the sedimentation process can be accelerated using fixed-angle and/or swinging bucket rotating centrifugation. Finally, after separation and characterization, nano and submicron phosphors were suspended and imaged through 5 mm thick porcine tissue using our in-house-built scanning X-ray induced luminescence chemical imaging (XELCI) system.

The Cover Feature shows in the first column of hexagons the exfoliation techniques used in the preparation of boron nitride nanosheets (BNNs) from hexagonal boron nitride. The SEM image in the background reveals high-quality BNNs with which thermally conductive polymer/BNN nanocomposites were developed (cf. right bottom corner). Two examples highlighting the heat dissipation capability and flexibility of BNN nanocomposites are shown in the second column of hexagons. More information can be found in the Review by Sriparna Bhattacharya, Apparao M. Rao, Rui Qiao, Ya-Ping Sun and co-workers.

SIGNIFICANCE:The ability to detect and localize specific molecules through tissue is important for elucidating the molecular basis of disease and treatment. Unfortunately, most current molecular imaging tools in tissue either lack high spatial resolution (e.g., diffuse optical fluorescence tomography or positron emission tomography) or lack molecular sensitivity (e.g., micro-computed tomography, μCT). X-ray luminescence imaging emerged about 10 years ago to address this issue by combining the molecular sensitivity of optical probes with the high spatial resolution of x-ray imaging through tissue. In particular, x-ray luminescence computed tomography (XLCT) has been demonstrated as a powerful technique for the high-resolution imaging of deeply embedded contrast agents in three dimensions (3D) for small-animal imaging. AIM:To facilitate the translation of XLCT for small-animal imaging, we have designed and built a small-animal dedicated focused x-ray luminescence tomography (FXLT) scanner with a μCT scanner, synthesized bright and biocompatible nanophosphors as contrast agents, and have developed a deep-learning-based reconstruction algorithm. APPROACH:The proposed FXLT imaging system was designed using computer-aided design software and built according to specifications. NaGdF4 nanophosphors doped with europium or terbium were synthesized with a silica shell for increased biocompatibility and functionalized with biotin. A deep-learning-based XLCT image reconstruction was also developed based on the residual neural network as a data synthesis method of projection views from few-view data to enhance the reconstructed image quality. RESULTS:We have built the FXLT scanner for small-animal imaging based on a rotational gantry. With all major imaging components mounted, the motor controlling the gantry can be used to rotate the system with a high accuracy. The synthesized nanophosphors displayed distinct x-ray luminescence emission, which enables multi-color imaging, and has successfully been bound to streptavidin-coated substrates. Lastly, numerical simulations using the proposed deep-learning-based reconstruction algorithm has demonstrated a clear enhancement in the reconstructed image quality. CONCLUSIONS:The designed FXLT scanner, synthesized nanophosphors, and deep-learning-based reconstruction algorithm show great potential for the high-resolution molecular imaging of small animals.

The optical and chemical properties of gold and silver nanoparticles make them useful for many applications, including surface enhanced spectroscopy-based biosensors, photostable colorants, enhanced photovoltaics, and nanoscale optical elements. We report a simple technique to generate patterns of gold and silver nanoparticles with controlled shape and shape-dependent optical properties using metal stamps to impress them onto a glass substrate or flexible polymers. The pressure flattens the nanoparticles, converting initially spherical nanoparticles into discs with reduced height and increased diameter. This deformation causes their localized surface plasmon resonance wavelength to red-shift. Nanoparticles were characterized by electron microscopy, atomic force microscopy, and dark field optical scattering spectroscopy. The deformed nanoparticle patterns had a lateral resolution limited by the nanoparticle diameter (single particles are partly flattened only where they contact the stamp). The method also (i) transfers the stamp's topography, with smooth stamps generating flattened nanoparticles with uniform height, and small changes in stamp height are evident in the nanoparticle height and scattering wavelength, and (ii) allows facile removal of undeformed nanoparticles using scotch tape, and patterns of deformed nanoparticles can be transferred to a thin polymer-film. The patterning process is simple and inexpensive. It can be performed by hand for demonstrations or artistic applications, with controlled force for plasmonics research, and potentially automated on reel-to-reel presses for large scale production.