Emre Arkan

Nanofibers are emerging as a crucial component in triboelectric nanogenerators (TENGs) to enhance energy extraction from dissipated mechanical work. Polymer fiber-based triboelectric nanogenerators (PF-TENGs) are particularly prominent due to their numerous advantages, such as facile synthesis, affordability, eco-friendly production, and the ability to integrate into a wide range of applications. However, due to the surface charge mitigation mechanism, its complex material network suffers from insufficient charge production. Thus, chemical modification of triboelectric polymer matrix through molecular design and processing of modified structures via materials engineering is a feasible mechanism to promote surface charge. Herein, we showed the synthesis and application of three novel NPB-based hole transport organic molecules to enhance charge production and improve the fabricated device output. Modifying the main molecular body with distinct side groups enabled us to play with the resonance and inductive effects of the molecules. This modification resulted in the ability to tune the HOMO levels of the molecules. The application of these molecules also gave rise to both structural and topological alterations of the nanofibers that changed the surface features of the fiber films. As for TENG parameters, this strategy produced, in turn, 52% and 74% enhancement in instant voltage and power values compared to the reference device under the same experimental conditions. Under external electrical loads, the increase in the voltage reached 50%, and the recorded maximum value was 598 V. In contrast, the highest current value of 52.5 µA corresponds to a 67% enhancement compared to the reference TENG. The outcome of this study provides a significant improvement of the materials processing methodology, which applies to future printable and flexible TENG devices and further contributes to material design for improved tribotronic systems using the integration of dielectrics and semiconductors.

The reversible intrusion and extrusion of non-wetting liquids into a porous matrix create the basis for a diverse group of energy applications such as molecular springs, shock absorbers, and nano-bumpers. These processes are mainly accompanied by heat exchange that has to be improved for efficient thermal and mechanical energy storage. In this paper, heterogeneous lyophobic systems (HLSs) have been created by mixing the highly porous zeolite imidazole framework (ZIF-8) with a phase change material (PCM) of sodium acetate trihydrate to enhance the energetic features of the system. The non-wetting behavior of the used PCM was confirmed by contact angle measurements. A scanning transitiometer was used for simultaneous measurements of the mechanical and thermal effects of three sodium acetate solutions (mass fraction of 0.203, 0.304 and 0.362) during the intrusion and extrusion process at 298.15 K and the sodium acetate trihydrate melt at 353.15 K. The results show that the higher the mass fraction of the sodium acetate solutions, the greater the intrusion pressure and heat effect. For the recorded heat values, this increase is more prominent when the salt solution approaches its saturation point and becomes ~ 2.6 times higher than previously obtained results with distilled water. The results indicated here provide a promising way to improve thermal energy storage for possible future engineering applications.

The wettability of nanoporous materials is a key property for a diverse range of applications. However, the heat generated in this process remains largely unexplored. Herein, the heats of intrusion/extrusion into/from ZIF-8 + water systems of various ZIF-8 crystallite sizes were measured at different temperatures. We found that decreasing crystallite size to the nanoscale resulted in a reduction of the magnitude of the heats of intrusion/extrusion. These results were mirrored in simulations, where the reduction of intrusion heat by reducing the characteristics dependent on crystallite size was comparable to the values obtained experimentally. We related this to the reduction in filling at lower pressures. We recorded the inversion of the sign of the heats of intrusion/extrusion measured at high temperatures. In addition, the heat/work ratio of the intrusion/extrusion processes was dependent on temperature while independent of crystallite size, decoupling the two parameters and making them tunable exogenously.

Wetting of a solid by a liquid is relevant for a broad range of natural and technological processes. This process is complex and involves the generation of heat, which is still poorly understood especially in nanoconfined systems. In this article, scanning transitiometry was used to measure and evaluate the pressure-driven heat of intrusion of water into solid ZIF-8 powder within the temperature range of 278.15-343.15 K. The conditions examined included the presence and absence of atmospheric gases, basic pH conditions, solid sample origins, and temperature. Simultaneously with these experiments, molecular dynamics simulations were conducted to elucidate the changing behavior of water as it enters into ZIF-8. The results are rationalized within a temperature-dependent thermodynamic cycle. This cycle describes the temperature-dependent process of ZIF-8 filling, heating, emptying, and cooling with respect to the change of internal energy of the cycle from the calculated change in the specific heat capacity of the system. At 298 K the experimental heat of intrusion per gram of ZIF-8 was found to be -10.8 ± 0.8 J·g^-1. It increased by 19.2 J·g^-1 with rising temperature to 343 K which is in a reasonable match with molecular dynamic simulations that predicted 16.1 J·g^-1 rise. From these combined experiments, the role of confined water in heat of intrusion of ZIF-8 is further clarified.

Current improvement in perovskite solar cells (PSCs) has been achieved by interface engineering and fine-tuning of charge-selective contacts. In this work, we report three novel molecules that can form self-assembled layers (SAMs) as an alternative to the most commonly used p-type contact material, PTAA. Two of these molecules have bidentate anchoring groups (MC-54 and MC-55), while the last one is monodentate (MC-45). Besides the PTAA comparison, we also compared those two types of molecules and their effect on the solar cell's performance. Devices fabricated with MC-54 and MC-55 showed a remarkable field factor (about 80%) and a better current density, leading to higher efficient solar cells in comparison to MC-45 and PTAA. Moreover, mono- and bidentate present higher stability and reproducibility in comparison to PTAA.

This study explores task-specific ionic liquids (TSILs) in smart floor systems, highlighting their strong electrical rectification abilities and previously established wood preservative properties. Two types of TSILs, featuring a “sweet” anion and a terpene-based cation, were used to treat selected wood samples, allowing for a comparison of their physical and electrical performance with untreated and commercially treated counterparts. Drop shape analysis and scanning electron microscopy were employed to evaluate the surface treatment before and after coating. Near-IR was used to confirm the presence of a surface modifier, and thermogravimetric analysis (TGA) was utilized to assess the thermal features of the treated samples. The different surface treatments resulted in varied triboelectric nanogenerator (TENG) parameters, with the molecular structure and size of the side chains being the key determining factors. The best results were achieved with TSILs, with the instantaneous voltage increasing by approximately five times and the highest voltage reaching 300 V under enhanced loading. This work provides fresh insights into the potential application spectrum of TSILs and opens up new avenues for directly utilizing tested ionic compounds in construction systems.

Molecular engineering is a unique methodology to take advantage of the electrochemical characteristics of materials that are used in energy-harvesting devices. Particularly in triboelectric nanogenerator (TENG) studies, molecular grafting on dielectric metal oxide surfaces can be regarded as a feasible way to alter the surface charge density that directly affects the charge potential of triboelectric layers. Herein, we develop a feasible methodology to synthesize organic–inorganic hybrid structures with tunable triboelectric features. Different types of self-assembled monolayers (SAMs) with electron-donating and withdrawing groups have been used to modify metal oxide (MO) surfaces and to modify their charge density on the surface. All the synthetic routes for hybrid material production have been clearly shown and the formation of covalent bonds on the MO’s surface has been confirmed by XPS. The obtained hybrid structures were applied as dopants to distinct polymer matrices with various ratios and fiberization processes were carried out to the prepare opposite triboelectric layers. The formation of the fibers was analyzed by SEM, while their surface morphology and physicochemical features have been measured by AFM and a drop shape analyzer. The triboelectric charge potential of each layer after doping and their contribution to the TENG device’s parameters have been investigated. For each triboelectric layer, the best-performing tribopositive and tribonegative material combination was separately determined and then these opposite layers were used to fabricate TENG with the highest efficiency. A comparison of the device parameters with the reference indicated that the best tribopositive material gave rise to a 40% increase in the output voltage and produced 231 V, whereas the best tribonegative one led to a 33.3% rise in voltage and generated 220 V. In addition, the best device collected ~83% more charge than the reference device and came up with 250 V that corresponds to 51.5% performance enhancement. This approach paved the way by addressing the issue of how molecular engineering can be used to manipulate the triboelectric features of the same materials.