The relationship between hydrophobicity and surface chemistry is crucial for optimizing materials used in vibration energy harvesting (VEH) applications, where environmental resilience and charge transfer efficiency are essential. Aluminum alloys, commonly used in the automotive, aerospace, and energy sectors, naturally develop an oxide layer that offers limited corrosion resistance in humid and saline environments. A promising strategy to improve performance and durability consists of modifying the wettability of aluminum surfaces .

In this study, we produced highly hydrophobic aluminum surfaces using a one-step etching method, yielding microstructured roughening of the surfaces that facilitates air trapping, enhancing hydrophobic behaviour. Contact Angle Goniometry (CA), Scanning Electron Microscopy (SEM), and X-ray Photoelectron Spectroscopy (XPS) were employed to correlate surface wettability with sub-micrometer-scale morphology and chemical composition. We found that surface hydrophobicity is governed by the interplay between hierarchical micro/nanostructures and the chemical composition of the outermost layers. We used the optimized aluminum surfaces for a portable VEH device, specifically leveraging Reverse Electrowetting on Dielectric (REWoD) technology, that efficiently harvests energy from low-frequency vibrations (<10 Hz) typical of human motion. We realized the device using off-the-shelf polyacrylamide (PAAm) hydrogels loaded with saline solutions using a heat treatment that extends the hydrogel drying times significantly. The laboratory prototype generated an average power of ∼1.55 μW at 7 Hz, achieving a power density of 9 nW/μl.

Plasma–particle interactions strongly influence the formation of atmospheric plasma-sprayed (APS) coatings . Especially for alumina, which usually undergoes a complex phase transformation of α-Al₂O₃ to metastable phases such as γ-, η- or δ-Al₂O₃ during thermal spraying, the heating and cooling behavior of the particles is of great importance.

This study therefore investigates the effect of plasma fluctuation and particle morphology on the melting behavior of aluminia and alumina-based powder particles. In particular, the impact of the degree of particle melting on the known phase transformation and the deposition efficiency is being investigated. In addition to the phase analysis of the coatings, powders collected during the spraying process were examined to evaluate their changes in the plasma. The particle morphology of the powders collected provides clear indications of their degree of melting. Moreover, both the plasma fluctuations and important particle parameters, such as particle temperature and velocity, are recorded.

The results show that the degree of particle melting in strongly linked to the plasma fluctuations, which can be significantly influenced by adjusting the process parameters. While higher α-Al₂O₃ contents in the collected powder cannot be transferred into the coating if they are attributed to non-melted particles, coatings with higher α-Al₂O₃ contents can be achieved by partially melted particles or the use of Al₂O₃-based solid solutions without negatively affecting the deposition efficiency.

The growing interest in the study of reversibly hydrogen-absorbing thin films is mainly due to their potential application as hydrogen sensors or switchable mirrors (smart windows) in electronics. From an economic point of view, magnesium would be the most suitable material for such applications. In contrast to bulk magnesium, Mg thin films covered with a palladium layer can absorb hydrogen at room temperature and pressures of up to 1 bar. One important experimental problem that still needs to be solved is the improvement of the too-slow absorption kinetics. This paper presents the results of studies leading to a significant improvement in hydrogen absorption kinetics by depositing an ultrathin Ni (Al or C) layer between the top Pd catalytic layer and the Mg base layer. A significant improvement in the absorption kinetics was also achieved by replacing pure Mg with a Mg₂Ni alloy. In addition, in order to determine the mechanisms responsible for the improvement of absorption kinetics, the effect of atom mixing in the interface region was studied in detail using X-ray photoelectron spectroscopy. The obtained results confirmed the important role of the Ni interlayer in improving hydrogen absorption kinetics in Pd/Ni/Mg trilayers. In Pd/Mg₂Ni bilayers, the Ni interlayer is formed spontaneously due to the segregation of Mg atoms on the surface. In the case of Al and C interlayers, the improvement of absorption kinetics occurs due to the spontaneous formation of small islands in the interface region containing Al atoms and magnesium carbide, respectively, which can form heterogeneous nucleation centres. The optimal thicknesses of Ni, Al and C layers are 3.0, 0.5, and 1.4 nm, respectively. The obtained results can be used to obtain new thin-film metallic nanomaterials with improved functional properties at room temperature.

Conventional methods for hydrogen peroxide (H₂O₂) synthesis, such as heterogeneous catalytic processes, require hydrogen (H₂) and oxygen (O₂) as feedstocks, along with expensive noble metals and organic solvents. These methods are energy-intensive and hazardous. In contrast, non-thermal plasma (NTP) generated within a dielectric barrier discharge (DBD) coaxial reactor provides 1 to 10 eV energy, sufficient to even drive thermodynamically unfavorable reactions by breaking molecular bonds. This study investigates the direct synthesis of aqueous H₂O₂ by passing oxygen through varying flow rates in a non-thermal plasma reactor. The outlet gas from the plasma reactor is then bubbled into water, facilitating H₂O₂ production. This method relies solely on water, oxygen, gas, and electricity, offering an environmentally friendly alternative to traditional processes.

This study also explores the role of a water–ethanol solution in enhancing product yield by approximately 10 times in the continuous production of concentrated aqueous hydrogen peroxide (H₂O₂). Experiments were initially conducted without catalysts, and the impact of various gas flow rates, plasma power, and residence time on conversion efficiency was examined. Electron Spin Resonance (ESR) studies indicate that oxygen radicals play a crucial role in the selective production of H₂O₂. Our findings present a proof-of-concept for utilizing low-cost aluminum electrodes in a dielectric barrier discharge (DBD) reactor, relying solely on electricity, water, and dioxygen for the generation of H₂O₂. This ongoing process ensures continuous improvement and provides the scalability needed to achieve high technology readiness levels.

Graphene-based materials exhibit a series of desired properties, e.g., electrical conductivity, high surface-to-volume ratio and tuning of surface chemistry between others, which make them a Swiss army knife for use in energy-related applications. In the present talk, I present the latest experimental results from our research on vertical graphene nanowall (VGNW) use in the above applications. VGNWs are characterized by the perpendicular orientation of graphene nanosheets with respect to the growth substrate, which is advantageous for homogeneous functionalization with other nanoparticles via vapor deposition techniques. I provide insights on the deposition of VGNWs as a coating on planar and three-dimensional nanostructured substrates via plasma chemical vapor deposition [1]. Then, I present results on the processing of VGNWs by laser pulses as a means to tune their crystal structure and control the density of defects [2]. I will conclude the talk showing the results on the preparation of VGNW-based compounds for application in electrocatalytic hydrogen evolution [3-5] and supercapacitor applications [6], focusing on their role as a template for the efficient anchoring of nanostructures.

References

[1] S. Chaitoglou, R. Amade, E. Bertran Applied Surface Science 592 (2022) 153327

[2] S. Chaitoglou, A. Klini, N. Papakosta, Y. Ma, R. Amade, P. Loukakos, and E. Bertran-Serra J. Phys. Chem. Lett. 15 (2024) 3779–3784

[3] S. Chaitoglou, R. Ospina, Y. Ma, R. Amade, X. Vendrell, J. Rodriguez-Pereira, E. Bertran-Serra Journal of Alloys and Compounds 972 (2024) 172891

[4] S. Chaitoglou, R. Amade, R. Ospina, E. Bertran ACS Appl. Energy Mater. 6 (2023) 6120-6131

[5] S. Rodriguez-Miguel, Y. Ma, G. Farid, R. Amade, R. Ospina, J. Luis Andujar, E. Bertran-Serra, S. Chaitoglou Heliyon 10 (2024) e31230

[6] Y. Ma, S. Chaitoglou, G. Farid, R. Amade, R. Ospina, A. Munoz-Rosas, E. Bertran-Serra Chemical Engineering Journal 488 (2024) 151135

Aluminium and its alloys are widely used in the automotive, aerospace, and marine industries due to their excellent mechanical properties and corrosion resistance. However, their susceptibility to corrosion in chloride-rich environments necessitates effective protection strategies. One promising approach is the development of superhydrophobic surfaces, which exhibit extreme water repellency (contact angle >150°) by combining hierarchical surface structures with low-surface-energy materials.[1,2]

This study aimed to enhance corrosion resistance and anti-icing properties by integrating laser surface structuring with stearic acid grafting. Different laser structuring parameters (selected scanning line spacings) were explored to optimize surface roughness before applying a stearic acid coating. Surface morphology, wettability, and roughness were analyzed using scanning electron microscopy, a contact profilometer, and a goniometer. Corrosion resistance was evaluated via electrochemical testing in 0.1 M NaCl, while the anti-icing effect and droplet-bouncing behaviour were assessed.

Results demonstrated that the optimal laser parameter (scanning line spacing) combined with stearic acid grafting significantly improved corrosion resistance and water repellency. This method offers a cost-effective, scalable approach for enhancing aluminium surfaces, making it suitable for applications requiring improved durability and anti-icing performance.

References:

[1] A. Bahgat Radwan, A.M. Abdullah, N.A. Alnuaimi, Recent advances in corrosion resistant superhydrophobic coatings, Corros. Rev. 36 (2018) 127–153. https://doi.org/10.1515/corrrev-2017-0012.

[2] P. Rodič, N. Kovač, S. Kralj, S. Jereb, I. Golobič, M. Može, I. Milošev, Anti-corrosion and anti-icing properties of superhydrophobic laser-textured aluminum surfaces, Surf. Coat. Technol. 494 (2024) 131325. https://doi.org/10.1016/j.surfcoat.2024.131325

Acknowledgements: The financial support from the Slovenian Research and Innovation Agency (ARIS) research core funding No. P2-0393, P1-0134, and P2-0223, and through the ARIS project, L2-60141, is acknowledged.

Surface functionalization plays a crucial role in advancing material performance across various industries, enabling tailored properties such as enhanced tribological behavior, improved wettability, increased adhesion, better biocompatibility, and superior optical characteristics. As demand grows for precise and efficient surface modification techniques, laser surface texturing (LST) has emerged as a promising technology due to its high precision, repeatability, productivity, and ability to create micro- and even nanoscale surface features with minimal material waste. Unlike conventional methods, LST offers a non-contact, environmentally friendly approach (as chemicals can be avoided) that allows for the localized and controlled modification of the surface topography and even chemistry, thereby optimizing the performance in applications ranging from biomedical implants to energy storage systems.

This communication explores the latest advancements in laser surface texturing, highlighting novel and emerging trends. These key developments include, among others, the production of extreme wetting surfaces (superhydrophilic or superhydrophobic), the production of self-cleaning surfaces, the potential of laser surface texturing to produce superior biomedical surfaces, and the application of laser surface texturing to control the corrosion behavior of biomaterials. By illuminating these evolving trends, this study aims at providing insights into the future potential of laser surface texturing as a transformative tool for next-generation functional surfaces.

When combining materials with divergent property profiles, such as polymers and metals, adhesion is mainly determined by mechanical interlocking—for example, in thermal joining or thermal spraying. For this, surface structuring is necessary in order to form undercuts and other adhesion-promoting profile elements. In this respect, laser-beam machining enables the production of complex structures, e.g., cone-like protrusions, grooves, or pins. However, despite a high flexibility in interface design, the influence of the scaling of profile elements has not been investigated so far. Although, understanding the effect of altering the initial surfaces on the functional properties, in particular the adhesion strength, offers potential for optimizing processing time or cost as well as overall adhesion performance. Therefore, the fractal dimension, a unitless measure of the structured interface, has been introduced previously, as it correlates quantitatively to the bonding shear strength. In this study, hence, the influence of structure scaling and the suitability of the fractal dimension as a strength prognosis criterion have been investigated on laser-beam-machined groove structures on aluminum 6082 prior to joining to polyamide 6. In parallel, modelled, virtual groove structures were considered for comparison. Finally, the fractal dimension served as a scale-independent measure, yielding similar values for constant aspect ratios for structures differing in their respective scale for both the model and experiment. Moreover, the adhesion strength in lap shear tests, ranging from 3.5–18.5 MPa, appeared independent of the scaling of profile elements for similar structure densities. So, a quantitative correlation of the fractal dimension of the interface to the adhesion strength could be confirmed and the influence of scaling could be excluded.

Introduction

Anode-free lithium metal batteries (AFLMBs) are promising for high-energy-density applications due to their reduced manufacturing complexity. However, challenges such as lithium dendrite formation, inactive lithium accumulation, and capacity degradation hinder their practical implementation [1]. This study explores a novel reagent-free approach to address these issues by leveraging laser-induced copper oxidation to enhance the electrochemical performance of AFLMBs.

Methods

Using a Nd:YAG laser under ambient conditions, a copper current collector (CC) was oxidized to produce controlled CuOx surface layers. The surface morphology and composition were analyzed using SEM, EDS, UV-Vis spectroscopy, Raman spectroscopy, and XRD. Electrochemical performance was evaluated through cyclic voltammetry, galvanostatic cycling, and impedance spectroscopy in half-cell and full-cell configurations.

Results

Laser-induced oxidation formed a CuOx layer that electrochemically converted to Li₂O during the first charge, creating a stable, artificial solid electrolyte interphase (SEI). This SEI reduced the lithium nucleation overpotential and enhanced uniform lithium deposition [2]. Moderately oxidized samples (Cu_LS1000) demonstrated optimal electrochemical performance, achieving >97% Coulombic efficiency over 100 cycles in half-cell tests and superior capacity retention in full-cell tests compared to unprocessed copper. Excessive oxidation (Cu_LS300) reduced the cycling stability due to increased polarization and lithium consumption during activation.

Conclusion

Laser-assisted copper oxidation is a scalable, cost-effective, and environmentally friendly technique for improving AFLMBs' safety and efficiency. The findings highlight the potential of precise surface engineering in advancing anode-free lithium battery technology, providing a pathway toward industrial scalability and enhanced energy storage solutions.

Transition metal oxide (TMO) nanostructures have attracted particular interest due to their multifunctionality, ranging from biomedical devices to electrochemical sensors for wastewater treatment in the textile industry, food processing and packaging, energy storage systems, catalysts, and solar cells. Among the different materials studied, In2O3 nanostructures have the advantages of remarkable physicochemical properties, high specific surface area, high surface-to-volume ratio, substantial chemical and environmental stability, and high electron mobility. Over the years, different substrates have been studied for the deposition of TMO thin films to meet the requirements of the targeted fields. In the present work, In₂O₃ nanostructures were obtained by chemical synthesis, and the process conditions and thermal treatment parameters were controlled, with these factors being considered the determining factors with effects on particle size and morphology. To ensure that the oxide nanostructures were compatible with the substrate of interest, graphene hydrophilization was performed. The next step consisted of dispersion of In₂O₃ powders in different media, drop-casting a suspension of oxide particles on the surface of the vertical graphene substrate, and evaporation of the solvent by heat treatment. The analytical methods used indicate a slight tendency of the particles to agglomerate at the surface but also to penetrate between the graphene sheets. FTIR spectroscopy studies and XRD diffraction measurements were carried out to determine their structure. The surface wettability was determined by measuring the contact angle to confirm the hydrophilicity. Furthermore, the electrochemical activities were investigated by cyclic voltammetry.

Acknowledgments: This work was supported by a grant from the Ministry of Research, Innovation and Digitization, CNCS-UEFISCDI, project number PN-IV-P2-2.1-TE-2023-0417, within PNCDI IV and by the Core Program within the National Research Development and Innovation Plan 2022-2027, project no. 2307.