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Volume 6
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Solids, Volume 6, Issue 2 (June 2025) – 5 articles

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19 pages, 8735 KiB  
Article
Binder Influence on Polyantimonic Acid-Based Membranes’ Electrical Behavior for Low-Temperature Fuel Cells
by Sofia Mendes and Pedro Faia
Solids 2025, 6(2), 19; https://doi.org/10.3390/solids6020019 - 17 Apr 2025
Viewed by 158
Abstract
The development of innovative proton-conducting materials for low-temperature fuel cells (FCs) is, today, a central topic among the scientific community. Polyantimonic acid (PAA) is characterized by high conductivity and sufficient thermal stability; however, PAA-based solid membrane fabrication with high proton conductivity remains challenging. [...] Read more.
The development of innovative proton-conducting materials for low-temperature fuel cells (FCs) is, today, a central topic among the scientific community. Polyantimonic acid (PAA) is characterized by high conductivity and sufficient thermal stability; however, PAA-based solid membrane fabrication with high proton conductivity remains challenging. Additionally, PAA cannot be compacted into solid shaped electrolytes without a binder. In a previous work, using a fluoroplastic binder, the authors fabricated and investigated proton conductivity of bulk PAA-based membranes in the temperature range 25–250 °C. In the present research, the authors opted to use another binder, poly(vinyl alcohol), PVA (which already allowed to obtain PAA sensors with higher sensitivity to moisture, low hysteresis, and similar aging than the produced previously with the fluoroplastic binder), for fabricating new solid membranes. The sample’s structure and morphology were studied using diverse experimental techniques (Thermogravimetric analysis, X-ray diffraction analysis, etc.). Electrical Impedance spectroscopy, EIS, was used to assess the electrical response and respective time stability of the membranes; it also allowed the development of an equivalent model circuit to better interpret the samples’ electrical behavior and respective contributions. The samples with 20 wt% PVA content showed improved protonic conductivity and chemical stability up to 100 °C, when compared to previous prepared and reported ones using the fluoroplastic binder. Full article
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23 pages, 4225 KiB  
Article
Modification of the Adsorption Capacity of Brick Industry Fly Ash for the Removal of Cd(II)
by León Fernando Pérez-Chauca, Luz Genara Castañeda-Pérez, Luis Américo Carrasco-Venegas, Juan Luis Quispe-Cisneros, Alfredo Torres-Garay and José Vulfrano González-Fernández
Solids 2025, 6(2), 18; https://doi.org/10.3390/solids6020018 - 16 Apr 2025
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Abstract
Fly ash, a byproduct of coal burning and gasification, is a significant source of global pollution and is classified as hazardous waste. However, physicochemical treatments can improve their adsorption capacity by increasing their surface area. This research aimed to enhance the adsorption capacity [...] Read more.
Fly ash, a byproduct of coal burning and gasification, is a significant source of global pollution and is classified as hazardous waste. However, physicochemical treatments can improve their adsorption capacity by increasing their surface area. This research aimed to enhance the adsorption capacity of fly ash from the brick manufacturing industry to remove Cd(II) ions by optimizing its surface area. The treatment process was designed with two factors: sodium hydroxide concentration and stirring time, each evaluated at three levels. The modification was confirmed through X-ray diffraction analysis of its mineralogical composition. Using the BET method, the initial fly ash exhibited a surface area of 8.59 m2/g, which increased to a maximum of 33.99 m2/g after treatment. The proposed modification method successfully quadrupled the surface area under optimal conditions: 2.0 M NaOH concentration and 60 min of stirring. The 32 factorial design shows that the highest degree of Cd(II) removal is 99.75%, which is achieved using the modified fly ash with a surface area of 33.99 m2/g under favorable operating conditions of 30 min and 600 rpm stirring speed. Full article
(This article belongs to the Special Issue Young Talents in Solid-State Sciences)
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18 pages, 7346 KiB  
Article
Optimizing the Mechanical Properties and Corrosion Performance of Low-Alloyed Mg-Zn-Ca Alloy by Regulating Zn/Ca Atomic Ratios
by Yuan Jin, Shaoyuan Lyu, Qianqian Yu and Minfang Chen
Solids 2025, 6(2), 17; https://doi.org/10.3390/solids6020017 - 14 Apr 2025
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Abstract
The microstructural, mechanical and corrosion properties of low-alloyed Mg-Zn-Ca alloys with different Zn/Ca atomic ratios were investigated. The results show that the microstructure of the extruded Mg-1Zn-0.3Ca (ZX1.0) alloy mainly consists of α-Mg and Ca2Mg6Zn3 phases and a [...] Read more.
The microstructural, mechanical and corrosion properties of low-alloyed Mg-Zn-Ca alloys with different Zn/Ca atomic ratios were investigated. The results show that the microstructure of the extruded Mg-1Zn-0.3Ca (ZX1.0) alloy mainly consists of α-Mg and Ca2Mg6Zn3 phases and a small amount of Mg2Ca phase. In contrast, the Mg2Ca phase disappears in the alloys Mg-1.4Zn-0.3Ca (ZX1.4), Mg-1.8Zn-0.3Ca (ZX1.8) and Mg-2.3Zn-0.5Ca (ZX2.3). The Ca2Mg6Zn3 phases are mainly distributed along the extrusion direction, showing irregular particle shapes and banded particles. Meanwhile, the grain size of the extruded Mg-Zn-Ca alloy is reduced gradually with the increase of the Zn and Ca contents, decreasing from 1.87 μm in ZX1.0 to 1.28 μm in ZX2.3 alloy. Fine grain strengthening and second-phase strengthening increase the yield strength and ultimate tensile strength of the alloy. In addition, when the Zn/Ca ratio is the same, the total elemental content dominates the effect on alloy properties. When increasing the Zn/Ca ratio, the potential difference between Ca2Mg6Zn3 and the Mg matrix increased, resulting in an increase in galvanic corrosion. The negative effect of the volume fraction of the second phase and the positive effect of the fine grain size determine the corrosion performance together. Therefore, ZX1.8 exhibits the best corrosion resistance, of 0.14 mm/y. Full article
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26 pages, 3432 KiB  
Article
Pristine and Reassembled Nanosheets of Layered Perovskite-like Titanates HLnTiO4 and H2Ln2Ti3O10 (Ln = La, Nd) as Photocatalysts for Hydrogen Evolution
by Sergei A. Kurnosenko, Oleg I. Silyukov, Ivan A. Rodionov, Iana A. Minich and Irina A. Zvereva
Solids 2025, 6(2), 16; https://doi.org/10.3390/solids6020016 - 2 Apr 2025
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Abstract
Layered Ruddlesden–Popper titanates HLnTiO4 and H2Ln2Ti3O10 (Ln = La, Nd) have been exfoliated into nanosheets in aqueous tetrabutylammonium hydroxide and systematically investigated as hydrogen evolution photocatalysts. The nanosheets were tested both in as-prepared pristine form [...] Read more.
Layered Ruddlesden–Popper titanates HLnTiO4 and H2Ln2Ti3O10 (Ln = La, Nd) have been exfoliated into nanosheets in aqueous tetrabutylammonium hydroxide and systematically investigated as hydrogen evolution photocatalysts. The nanosheets were tested both in as-prepared pristine form and after reassembly by two methods (simple filtration and precipitation by hydrochloric acid). The nanosheet-based samples demonstrated by up to 88 times greater photocatalytic performance in comparison with the bulk precursors and, after modification with a Pt cocatalyst, provided apparent quantum efficiency of hydrogen generation up to 14.2% in 1 mol.% aqueous methanol and 3.15% in pure water. It was established that the form in which the nanosheets are used strongly affects the hydrogen production efficiency: the latter typically decreases when moving from the pristine nanosheets to filtered ones and then to those restacked by hydrochloric acid, which is determined by the difference in their physical–chemical characteristics being influenced by the reassembly approach. Full article
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18 pages, 18008 KiB  
Article
Insights into the Electrochemical Synthesis and Supercapacitive Behaviour of 3D Copper Oxide-Based Nanostructures
by Gintautas Jonkus, Ramunas Levinas, Natalia Tsyntsaru and Henrikas Cesiulis
Solids 2025, 6(2), 15; https://doi.org/10.3390/solids6020015 - 1 Apr 2025
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Abstract
In this study, nanostructured copper oxide-based films with crystallite size below 10 nm were electrochemically synthesized on copper foil and foam electrodes and investigated for their supercapacitive behaviour. The synthesis was carried out via cyclic voltammetry (CV) for up to 1000 cycles in [...] Read more.
In this study, nanostructured copper oxide-based films with crystallite size below 10 nm were electrochemically synthesized on copper foil and foam electrodes and investigated for their supercapacitive behaviour. The synthesis was carried out via cyclic voltammetry (CV) for up to 1000 cycles in an alkaline electrolyte. By tuning the upper vertex potential (−0.3 V to 0.65 V vs. Ag/AgCl), both phase composition (Cu2O, Cu(OH)2, CuO) and morphology (grains, nanoneedles, nanoplatelets) were precisely controlled, demonstrating the versatility of this approach. The kinetics of oxide/hydroxide film formation on foil and foam electrodes were analysed based on EIS data that were interpreted in the frame of equivalent electric circuits and their changes with potential. The capacitive properties of the synthesized films were evaluated using CV in the potential range of 0 V–0.65 V, and the optimized CuO film synthesized on Cu foam exhibited a high specific capacitance of 1380 mF cm⁻2. An energy density of 0.061 mWh cm−2 and power density of 1.28 mW cm−2 were obtained at 10 mA cm−2 discharge current. Charge–discharge cycling at 100 mV s−1 for 1000 cycles indicated an initial capacitance increase followed by stable retention, highlighting the structural integrity and electrochemical stability of the films obtained on 3D foam. These findings provide valuable insights into the controlled electrochemical synthesis of copper oxide nanostructures and their potential for high-performance capacitor applications. Full article
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