Hydrogen

The ratio of hydrogen isotopes—protium and deuterium—in water significantly influences the physicochemical and biological properties of dissolved pharmaceutical substances. This study investigated the impact of water isotopic composition on both the kinetic parameters and biological activity of amoxicillin (AMX) and Zn²⁺ solutions. The kinetics of complexation were examined fluorometrically in waters with varying D/H ratios: H₂O (D/H = 145 ppm), heavy water (D₂O, 99.9%), and deuterium-depleted water (DDW, D/H = 10 ppm). The fluorescence intensity of the solutions increased significantly with higher deuterium content in the solvent: I_D2O/I_DDW = 1.5. The addition of Zn²⁺ induced the changes in fluorescence intensity. The isotope effects k_H2O/k_D2O = 1.9 and k_H2O/k_DDW = 2.2 indicate the involvement of water molecules in the rate-limiting step of the process. The decrease in biological activity of AMX due to complexation was confirmed using the biosensor Spirostomum ambiguum. Depletion of D/H and ¹⁸O/¹⁶O ratios in water increases the biosensor’s lifetime. The longest biosensor lifetime was observed in heavy-isotopes-depleted water (HIDW, D/H = 10 ppm, ¹⁸O/¹⁶O = 400) solutions. Therefore, the variations in the isotopic composition of water from different regions should be considered in the preparation of liquid dosage forms and in the quality control of drugs.

Hydrogen sulfide (H₂S) is a toxic sulfur-containing by-product generated in refining, gas processing, and decomposition processes. Its electrochemical treatment under alkaline conditions offers a potential route for simultaneous hydrogen production and sulfide conversion. Although alkaline sulfide electrolysis has been investigated for several decades, quantitative information on the performance of industrial corrosion-resistant electrodes remains limited. In this work, industrial NiCrMo276 alloy electrodes were evaluated for hydrogen production in a batch alkaline sulfide electrolysis system. Graphite was used as a reference material in an initial electrode screening, in which NiCrMo276 exhibited a substantially higher current response under identical electrolysis conditions. Based on this screening, NiCrMo276 was selected for subsequent evaluation of the effects of applied cell voltage and NaHS concentration on the electrochemical response. At an applied cell voltage of 1.8 V and a NaHS:NaOH molar ratio of 1.25:1, hydrogen was produced at 200 mL h⁻¹, corresponding to a current density of 33 mA cm⁻² and a Faradaic efficiency of 92%. The specific electricity consumption was 52.4 kWh kg⁻¹ H₂. Complementary sulfur analyses indicated incomplete sulfide conversion and a marked evolution of the dissolved sulfur composition, particularly toward thiosulfate, although the measured sulfur distribution could not be attributed exclusively to electrochemical reactions. Post-electrolysis SEM–EDX observations showed that NiCrMo276 retained a relatively well-defined surface morphology, particularly at the cathode, while the graphite surface exhibited substantial intrinsic heterogeneity. Overall, the combination of high Faradaic efficiency, hydrogen productivity, and substantially higher current response than graphite highlights NiCrMo276 as a promising electrode material for alkaline sulfide electrolysis.

The rapid expansion of hydrogen production from low-carbon sources requires large-scale, flexible and reliable storage solutions to balance supply and demand and support the integration of hydrogen into future energy systems. Underground hydrogen storage, and particularly storage in salt caverns, offers significant potential due to the favorable characteristics of salt formations and the possibility of storing and recovering large quantities of hydrogen. However, identifying and comparing prospective storage sites requires the simultaneous consideration of geological suitability, uncertainty in the available data, operating characteristics, and project-specific requirements. Existing screening approaches generally address only subsets of these aspects, limiting their applicability to comprehensive site comparison and ranking. This study develops a holistic Decision-Making Tool (DMT) for the preliminary screening and comparative ranking of potential hydrogen storage sites in salt formations. The methodology integrates four complementary information categories: Static, Static-Probabilistic, Dynamic, and Operator’s data. Deterministic suitability assessment, Monte Carlo-based uncertainty propagation, engineering feasibility calculations of hydrogen storage performance, and operator-defined requirements are sequentially combined into a scenario-dependent final ranking. The methodology has been implemented in an Excel-based, transparent tool, allowing multiple candidate sites and alternative storage scenarios to be evaluated without changing the underlying calculation framework. Application to three prospective evaporite areas in western Greece demonstrates the ability of the tool to distinguish between sites not only according to geological suitability but also according to data confidence, storage performance and proximity to hydrogen production and consumption hubs. The resulting framework provides a practical bridge between early-stage geological screening and engineering-oriented site selection, while retaining the flexibility to adapt the ranking to different project objectives and levels of decision-making.