Andris Šutka

A liquid metal approach synergised by a bridge solubility strategy is employed for incorporation of insoluble nonmetal fluorine into liquid tin, allowing harvesting of ultrathin F-doped SnO ₂ as a transparent conductive oxide.

This study introduces an ultrasound-powered contact-electro-catalysis (CEC) method for degrading 4-hydroxybenzoic acid (HBA) using polytetrafluoroethylene (PTFE) microparticles. Under neutral conditions, the system achieved over 99% HBA degradation in aqueous solutions. Mechanistic analysis confirms that hydroxyl radicals act as the primary oxidants. HBA degradation proceeds via primary hydroxylation and secondary decarboxylation pathway. The effects of acidic and alkaline conditions were investigated, demonstrating the non-innocent role of counter ions. Furthermore, recycling tests showed that the PTFE catalyst retains high structural integrity and consistent degradation efficiencies (96%–99%) of HBA across consecutive cycles. These findings demonstrate the potential of ultrasound-driven CEC as a robust technology for wastewater remediation.

The growth of wearable electronics has intensified the search for sustainable, high-performance materials for integration into smart sensing platforms. Conventional piezoelectric polymers, particularly fluorinated systems, offer excellent electromechanical transduction; however, they pose environmental and end-of-life challenges. Here, we demonstrate a recycled expanded polystyrene (PS) triboelectric laminate as an acoustic neuromorphic sensor. The multilayered structure of the triboelectric laminate enables a mechanoelectric response similar to that of piezoelectric polymers. The triboelectric laminate sensor was integrated into the face mask and generated current signals in the range of 4 nA (peak-to-peak) with distinct features in response to speech signals of various words. To exploit the recorded signals for dynamic speech recognition, we develop an interpretable physics-guided staged ML framework named Triboelectric Lexical Network (TriboLexNet), which learns the spectral signatures and combines time-frequency descriptors embedded into a random-forest framework. TriboLexNet is capable to recognize the specific word in the sentences, with a held-out segment-level accuracy of 99.4 ± 0.9% and a per-recording keyword-detection accuracy of 89.6 ± 6.4% under strict recording-level data partitioning, as well as locating it in terms of an interpretable probability distribution. Our approach establishes a viable platform for sustainable triboelectric acoustic neuromorphic sensing and demonstrates how physics-guided ML can be utilized in dynamic speech recognition with limited data.

Contact electrification occurs when two materials rub against one another. This is either a problem, such as when charge builds up during powder processing, or an exploited phenomenon to harvest energy, as is the case in triboelectric nanogenerators. However, why contact electrification occurs remains a topic of hot debate, with ions, adsorbates, electrons and combinations thereof being ascribed the charge carriers. Irrespective of the charge carrier however, there must be a driving force inducing charge to separate and move from one surface to another. Herein, we demonstrate that electric fields, either applied externally or spontaneously generated at an interface can completely alter and even invert surface charge measured after contact electrification in polymer-polymer contact. Applying an external electric field allows the direct control of both magnitude and polarity static charge on dielectric polymers. These results are coupled to simulations that show the applied electric field is on the order of the fields generated by the flexoelectric effect – providing prima facie evidence of flexoelectric driven contact electrification.

Residual solvents are an often-overlooked factor that may influence the triboelectric performance of solution-processed polymer films. Here, the effect of solvent evaporation dynamics on triboelectric charging was investigated using poly(vinylidene fluoride) (PVDF)/N,N-dimethylformamide (DMF), ethylene-vinyl acetate (EVA)/toluene, and polyether block amide (PEBA)/chloroform systems. Residual solvent evolution was monitored by ATR-FTIR spectroscopy, while surface roughness, Kelvin-probe contact potential difference, and triboelectric charge density were measured as a function of drying time. All three systems exhibited time-dependent changes in triboelectric charge density after film deposition. The strongest effect was observed for PVDF/DMF, where decreasing DMF-related FTIR bands coincided with a substantial reduction in triboelectric charge. EVA/toluene and PEBA/chloroform films also showed drying-dependent changes despite limited or absent spectroscopic evidence of the residual solvent, indicating contributions from post-deposition film equilibration. The results demonstrate that triboelectric properties can evolve significantly after film formation and that measurements performed before complete equilibration may not reflect the intrinsic behaviour of the material. These findings identify drying history as a critical parameter in the characterization and comparison of triboelectric materials.

Triboelectric nanogenerators (TENGs) are a key emerging technology for powering wearable, implantable, remote, and autonomous small-scale electronics. Despite extensive reports, there is often a lack of rigor in reporting the mechanical testing conditions used to measure electrical performance in TENGs. Herein, we systematically vary the separation speed in contact–separation TENGs between 12.5 and 700 mm s–1 (both experimentally and via simulations) and measure a corresponding increase in power density from 10–7 to 10–4 W (along with analogous increases in measured current and voltage)-without changing any other material property or parameter. The transferred charge density (on the external electrodes, as separate from the surface charge density) also increased from 0.3 to 10 nC cm–2, demonstrating (along with supporting computational simulation experiments) that large changes in measured output can arise from testing conditions rather than changes in material chemistry or device structure. These results demonstrate the importance of separation speed in contextualizing literature reports of TENG performance and highlight the need to dramatically improve data reporting for the field. To address this, we propose the need to report a standard and consistent set of testing parameters for contact separation. Adoption of these conditions will enable meaningful benchmarking of TENGs and allow the field to progress more effectively.

Over the past decades, the investigation of contact electrification (CE), also called triboelectrification, and its dependence on material and environmental parameters has garnered increasing attention. Specifically, water CE has taken a significant role in energy harvesting, chemical synthesis, and sensing. However, many parameters that influence the observed charge generation remain unstudied. In this work, we report the effects of polymer properties and droplet dielectric properties on solid-liquid CE. First, we analyze the influence of the solid triboelectric material on the signal by comparing various polymers to identify the configuration that maximizes the electrical output generated by deionized water droplets. Then, we examine the triboelectric response of different liquid solutions, specifically ethanol and polyethyleneimine (PEI) solutions at varying concentrations, which modulate the dielectric constant of the droplets. Our results indicate a positive correlation between the dielectric constant of the liquid and the generated current for a given polymer. The perfluoroalkoxy (PFA) surfaces generated a short-circuit current density (JSC) of -9.9µA/cm2 upon interaction with ethanol droplets with a dielectric constant of 65. For PEI droplets with a dielectric constant of 120, the JSC signal was -116 µA/cm2. Thus, we obtained a 12-fold increase in short-circuit current density by simply doubling the dielectric constant of the droplet. This study not only advances the understanding of liquid–solid triboelectrification mechanisms but also provides a pathway to optimize the electric response.

Solid–liquid contact electrification is widely studied using diverse experimental geometries that are often implicitly assumed to probe equivalent interfacial processes. Here, we directly test this assumption by comparing immersion–emersion, droplet-based contact, and pressure-driven intrusion–extrusion electrification using the same hydrophobic nanoporous silicon monolith and isotopically substituted liquids (H2O and D2O). Despite identical surface chemistry, isotopic substitution produces qualitatively different electrical responses depending on the wetting regime. Immersion–emersion experiments show polarity inversion between H2O and D2O, while droplet measurements reveal distinct charge evolution and periodic opposite-polarity events. In contrast, forced nanopore intrusion preserves polarity but strongly enhances electrical output for D2O. These results demonstrate that wetting of surface nanoroughness during droplet, vs immersion–emersion, vs complete nanopores wetting upon intrusion–extrusion correspond to fundamentally different electrification states. By using isotope substitution as a controlled probe, this work establishes a general framework for disentangling protocol-dependent effects in solid–liquid contact electrification and triboelectric energy conversion.

Triboelectric nanogenerators (TENGs) are major drivers in on-site power generation for smart devices, enable self-powered sensors, and introduce novel catalytic processes. Here, we demonstrate adamantane plasma polymers as versatile dual-polarity triboelectric surfaces capable of exhibiting either tribopositive or tribonegative behavior through simple control of the plasma deposition configuration, without additives or post-functionalization. By modifying the substrate orientation relative to the plasma, thin-film polymers with distinct dielectric, mechanical, secondary electron emission, and triboelectric properties are obtained. The high conformality, stability, and processability of the polymers enable their direct implementation into solid-solid, solid-liquid, and hybrid piezo-triboelectric configurations. Additional surface texturization through buckling provides voltage and current outputs as high as 90 Vpeak-to-peak and 0.6 µA cm-2 for a 2.8 µm (tribonegative) vs. 400 nm (tribopositive) combination with a maximum mean power density of 2.1 µW cm-2. A maximum peak power of 200 µW is generated from salty droplets in drop-TENG configuration employing a 500 nm-thick tribopositive adamantane polymer. These layers sustain more than 105 cycles in solid-solid nanogenerators and 104 droplet impacts in solid-liquid devices. Combined with an environmentally friendly and industrially scalable synthesis route, these results position adamantane plasma polymers as a robust and versatile platform for next-generation triboelectric energy-harvesting materials.