Abraham Méndez-Reséndiz

Alkaline hydrogen evolution is kinetically limited by water dissociation and by the structural degradation of non-precious electrocatalysts during prolonged operation. Here, we investigate how NiS loading influences phase distribution, surface chemistry, charge-transfer characteristics, and durability when supported on N,S co-doped hollow carbon spheres (NSHCS). Catalysts containing 5 and 20 wt.% NiS were synthesized and compared with analogous materials supported by undoped hollow carbon spheres (HCS). Structural and surface analyses reveal that decreasing the NiS loading suppresses the formation of secondary phases (Ni3S4 and NiSO4), promotes a more homogeneous dispersion of sulfide domains, and reduces the extent of surface sulfate formation, particularly within the heteroatom-doped framework. Electrochemical measurements in 0.1 mol L-1 KOH show that 5-NiS/NSHCS exhibits a charge-transfer resistance of approximately 10 Ω, compared with values exceeding 1 kΩ for 5-NiS/HCS, together with 92% current-density retention after 5000 accelerated degradation cycles. The improved electrochemical response correlates with enhanced sulfide-phase dispersion and a sulfide-rich surface environment, suggesting that heteroatom-mediated metal–support interactions facilitate charge transfer and help preserve catalytically active sites during operation. These findings demonstrate that HER durability is governed more strongly by active-phase distribution and interfacial interactions than by nominal NiS loading, providing insight into the design of durable alkaline HER electrocatalysts based on earth-abundant sulfides.

Two-dimensional (2D) materials, particularly MXenes and transition metal dichalcogenides (TMDs), have attracted intense interest as supercapacitor electrodes due to their high surface area and tunable electronic structure. However, large discrepancies persist between the quantum capacitance values predicted by density functional theory (DFT) calculations and experimentally measured gravimetric capacitances. In this review, we critically analyze DFT methodologies, surface models, normalization strategies, and electrochemical characterization protocols, and compile an extensive dataset of reported MXene and TMD systems to quantify the degree of experimental–theoretical agreement. We show that MXenes typically achieve less than 20% of their predicted capacitance because of restacking, surface terminations, and limited ion accessibility, whereas TMDs exhibit substantially better correspondence, often approaching or exceeding 70% of theoretical values. These results indicate that the theoretical capacitance predicted by DFT is primarily determined by the electronic structure of the material, which defines the upper limit of charge storage, whereas the experimentally achieved capacitance is largely controlled by morphological factors, surface chemistry, and electrode architecture that limit ion accessibility.

Hydrogel electrolytes were synthesized using polyvinyl alcohol (PVA) and various graphene derivatives, including graphene oxide (GO), exfoliated graphene (GEX), reduced graphene oxide (rGO), and selectively oxidized graphene (SOG). The effects of these graphene derivatives on the gel structure were analyzed using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and rheological measurements. Additionally, the influence of the water-to-ethylene glycol ratio on the gel properties was assessed. Incorporating graphene derivatives enhanced hydrogen bonding within the hydrogel network, depending on the oxygen functional groups and defect density of the graphene materials, leading to improved structural stability. While ethylene glycol contributes to the gel formation, adding graphene derivatives further enhances the hydrogel’s mechanical properties, maintaining a high storage modulus and preserving ionic conductivity. These findings provide valuable insights for developing supercapacitors with an optimal balance between mechanical strength and energy storage efficiency.

Water repellency has significant potential in applications like self-cleaning coatings, anti-staining textiles, and electronics. This study introduces a novel nanocomposite system incorporating functionalized Al₂O₃ and CeO₂ nanoparticles within a polyurethane matrix to achieve hydrophobic and UV-blocking properties. The nanoparticles were functionalized using an octadecyl phosphonic acid solution and characterized by FTIR and XPS, confirming non-covalent functionalization. Spin-coated polyurethane coatings with functionalized and non-functionalized Al₂O₃, CeO_2, and binary Al₂O₃-CeO₂ nanoparticles were analyzed. The three-layered Al₂O₃-CeO₂-ODPA binary system achieved a contact angle of 166.4° and 85% transmittance in the visible range. Incorporating this binary functionalized system into a 0.4% w/v polyurethane solution resulted in a nanocomposite with 75% visible transmittance, 60% at 365 nm UV, and a 147.7° contact angle after three layers. These findings suggest that ODPA-functionalized nanoparticles, when combined with a polymer matrix, offer a promising approach to developing advanced hydrophobic and UV-protective coatings with potential applications across various industrial sectors.

Background: Cu2ZnFeS3 (CZIS) thin films were grown as a non-toxic material for use in photovoltaic cells as an n-type semiconductor. This material could work in synergy with p-type materials already existing in the market such as CdTe and Cu(In, Ga)Se2 (CIGS). Thin films of CZIS were grown as a quaternary Cu2ZnFeS3 material by the co-evaporation technique under high vacuum from binary sulfides such as iron sulfide (FeS2), copper sulfide (CuS) and zinc sulfide (ZnS), each one individually optimized and characterized. Methods: In this work, the results were performed using different variants such as thermal annealing step in two different atmospheres such as under vacuum, and vacuum-sulfur and also at different temperature (500-600ºC) in order to obtain quaternary materials. The structural, optical, morphological, compositional, and electrical properties of the samples were characterized using X-ray diffraction, UV-Vis spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and Hall effect measurements. XPS results indicate that the samples are slightly rich in Zn and poor in Cu. Conclusion: The evidence of surface oxidation has also been noted. Nevertheless, the depth profile did not show a significant change in the signal or in the composition in the composition. From the UV-Vis analyzes, we obtained optical band gap values with 2.22 < Eg < 2.76 eV. The carrier concentrations were found to be in the range of 3.3 x1020 to 4.6x1021 cm-3, the mobility value was around 4.45-0.22 cm2 V-1s-1, and the resistivity values were determined in the range of 1.68x10-3 to 1.89x10-2 Ω-cm.