Search Results (679)

Hydrogen (H₂) is a common product of carbohydrate fermentation by the intestinal microbiota, transferred to the blood along the pressure gradient, and exhaled. As H₂ is not produced or metabolized in human cells, alveolar H₂ is distributed throughout the human body, including cellular organelles such as mitochondria, owing to systemic circulation and gas exchange. The electron transport chain comprises a series of oxidation–reduction (redox) enzymes in the mitochondria of human cells that facilitate adenosine triphosphate (ATP) synthesis. The catalytic activity of electron-transport enzymes is optimized at certain electrochemical potentials, as is hydrogen ion activity (pH). However, the human body is an aqueous system that must be electrically neutral. Membrane potentials exist between the interior and exterior of human cells because of the unequal distribution of ions across the membrane. The single-electrode potential can only be assessed relative to that of another electrode (i.e., a reference electrode). The electrochemical potentials relative to a standard hydrogen electrode (SHE) were measured; it was found that H₂ partial pressure was a fundamental factor that affected the SHE, pH, and the reversible hydrogen electrode. The H₂ partial pressure is not a unit used to characterize the human body; therefore, breath H₂ is an external variable in the redox environment in the human body. Full article

The design of efficient small-scale hydrogen energy storage systems requires balancing hydrogen production rate, electrical efficiency, and system simplicity. This study experimentally investigates the energetic compromise imposed by separator material and electrolyzer architecture through a comparative analysis of finite-gap alkaline, finite-gap acidic, and zero-gap proton exchange membrane (PEM) electrolyzers. Zirfon^® Pearl 500 (Agfa, Mortsel, Belgium) diaphragms were employed in alkaline electrolysis using 25 wt.% KOH, whereas Nafion™ 117 (Chemours, Wilmington, DE, USA) membranes were used in both finite-gap acidic electrolysis (2.55 M H₂SO₄) and a commercial five-cell zero-gap PEM electrolyzer supplied with deionized water. Electrochemical performance was evaluated in terms of polarization behavior, apparent resistance, hydrogen production rate, Faradaic efficiency, and energy conversion efficiency. The zero-gap PEM architecture exhibited the best electrochemical performance, with an apparent resistance of only 0.138 Ω per cell, corresponding to reductions of approximately 43-, 51-, and 64-fold compared with the finite-gap PEM, stainless steel/Zirfon alkaline, and nickel/Zirfon alkaline configurations, respectively. The zero-gap electrolyzer delivered currents from 1.53 to 10.0 A while operating below 2.8 V, demonstrating the benefit of minimizing the ionic transport path. In contrast, the finite-gap acidic configuration achieved higher hydrogen production rates than the alkaline system owing to the superior proton conductivity of Nafion™ 117, whereas the alkaline Ni/Zirfon configuration reached the highest Faradaic efficiency (≈98%) and energy conversion efficiency (≈36%) because of improved gas separation and reduced hydrogen crossover. Electrochemical impedance spectroscopy further revealed that the normalized ohmic resistance of the zero-gap PEM cell was only 0.029 Ω, with charge-transfer processes accounting for approximately 96.2% of the total impedance. These results demonstrate that separator properties and cell architecture govern the trade-off between reaction kinetics and energy efficiency, providing practical guidelines for selecting electrolyzer configurations dedicated to decentralized and small-scale hydrogen energy storage. Full article

This study investigates machine learning techniques for predicting the behavior of proton exchange membrane electrolyzers, which are vital for sustainable hydrogen production. This work addresses these challenges by integrating artificial neural networks to develop predictive models capable of capturing the performance of proton exchange membrane electrolyzers with high accuracy. This research utilizes a multi-layer perceptron network architecture, optimized through rigorous data preprocessing, parameter tuning, and error minimization strategies. The dataset used was based on published PEME numerical simulation datasets and encompasses key performance indicators, including stack voltage, water transport, and electrochemical reactions. The trained artificial neural networks models achieved mean squared error values of 3.66 × 10⁻⁵ and 9.75 × 10⁻⁶, with correlation coefficients of 0.99996 and 0.99958, demonstrating near-perfect predictive accuracy. A comparative benchmarking study against alternative regression algorithms revealed that the proposed MLP models significantly outperformed Gradient Boosting and Random Forest by several orders of magnitude, thereby establishing a higher level of persuasiveness and reliability for the developed framework. Average deviation rates of 0.11% and −0.01% further validated model reliability. The novelty of this work lies in its comprehensive approach, which goes beyond isolated metrics by addressing interactions across system parameters. This integrated framework enables enhanced prediction, control, and optimization of proton exchange membrane electrolyzer’s performance, setting a new benchmark for leveraging machine learning in hydrogen energy systems. These findings pave the way for scalable, cost-effective solutions to improve proton exchange membrane electrolyzers’ efficiency and operational reliability. Full article

The piezocatalytic activity of metal–organic frameworks (MOFs) is generally hampered by an insufficient intrinsic piezoelectric response, which largely restricts their application in energy catalytic conversion. Herein, MIL-125-NH₂(Ti) (denoted NM) was chosen as a prototypical model to demonstrate that defect engineering serves as an efficient strategy to simultaneously reinforce the piezoelectric characteristics and piezocatalytic hydrogen evolution performance of MOFs. Multiple comprehensive characterizations verify that thermally treated NM-250 (NM thermally treated at 250 °C under flowing N₂ atmosphere) contains abundant in situ-generated oxygen vacancies. These defects disrupt the high intrinsic structural symmetry of pristine NM and promote the establishment of polarized electric fields upon mechanical excitation. Electrochemical measurements further reveal that the introduced oxygen vacancies effectively suppress charge carrier recombination and accelerate interfacial charge transfer, thereby facilitating the piezocatalytic hydrogen evolution reaction. Benefiting from the optimized piezoelectric polarization and improved charge separation efficiency, NM-250 delivers a piezocatalytic H₂ production rate of 413.5 μmol g⁻¹ h⁻¹, exceeding the value of pristine NM (180.9 μmol g⁻¹ h⁻¹) by 2.28 times. This work elucidates the underlying mechanism by which oxygen vacancy defects modulate piezoelectric polarization and catalytic kinetics and validates defect engineering as a promising route to construct high-performance MOFs-based piezocatalysts. Full article

Efficient small-scale hydrogen production via proton exchange membrane (PEM) electrolysis is a key pathway for advancing green hydrogen technologies. This study experimentally investigates a five-cell zero-gap PEM electrolyzer stack to evaluate energy losses, thermal behavior, and hydrogen generation efficiency. Faradaic efficiency increased with current density, reaching 98.03% at 0.232 A·cm⁻², while infrared (IR) thermography reveals non-uniform temperature distributions across the electrolyzer stack, with inter-cell and in-plane temperature gradients exceeding 9 °C. Although increasing current density led to higher ohmic and electrochemical losses, energy efficiency increased from 39.4% at 0.106 A·cm⁻² to 56.28% at 0.232 A· cm⁻², as the reduced relative contribution of activation overpotential predominated over the increase in resistive losses within the investigated range. The results demonstrate the strong coupling between electrochemical resistance growth, thermal gradients, and reduced hydrogen production efficiency. Overall, these findings underscore the importance of optimized thermal management and operating strategies for improving the performance and durability of small-scale PEM electrolyzers in green hydrogen applications. Full article

Carbon capture is more and more often seen as a component of an integrated carbon-management system than as a stand-alone separation phase. The practical utility of capture technology depends on the chemical state in which the carbon dioxide is held, the energy and material needs for regeneration, the compatibility of the caught species with downstream catalysis and the lifetime of the resulting carbon-containing product. This paper offers an in-depth framework for integrated CO₂ capture and circular carbon use, including catalytic conversion, bio-integrated processes, biomass-derived materials and fuels, hydrogen-enabled routes, mineralization, and artificial intelligence-assisted process design. Reactive capture techniques that convert carbonate, bicarbonate, carbamate, dissolved CO₂ or surface-bound intermediates without first generating a purified gas stream are contrasted with sequential capture, purification, compression, transport and conversion. The thermocatalytic, electrochemical, photoelectrochemical and biological conversion pathways are compared against common parameters such as working capacity, conversion rate, selectivity, carbon efficiency, regeneration energy, stability and life-cycle greenhouse gas performance. Special emphasis is given on dual-functional materials, interfacial reactors, bio-integrated methanation, carbon mineralization in construction materials and coupling with renewable hydrogen. The review also discusses how machine learning, molecular screening, process simulation, graph-based data architecture, and digital monitoring could speed up material selection and system optimization. Across all pathways, the central design requirement is not maximum capture capacity alone, but a balanced match among binding strength, transport, catalytic reactivity, product separation, durability, and carbon permanence. A reporting framework and research agenda are proposed to guide credible scale-up and comparison of integrated carbon-management technologies. Full article

The development of sustainable and low-cost electrocatalysts based on Earth-abundant elements is essential for the large-scale deployment of green hydrogen production via anion exchange membrane water electrolysis (AEMWE). Herein, we demonstrate the feasibility of cobalt-free high-entropy oxide (HEO) electrodes for AEMWE through a set of spinel oxides based on equimolar Cr, Mn, Fe, Ni, and Zn. The HEOs were synthesized by a scalable sol-gel route followed by calcination at different temperatures (400–800 °C). The pristine oxides were employed as oxygen evolution reaction catalysts, whereas their H₂/Ar-reduced counterparts were used as hydrogen evolution reaction catalysts in symmetric membrane electrode assemblies (MEAs). Comprehensive physicochemical characterization combined with electrochemical testing revealed that the phase purity of the anodic catalyst mainly correlates with both the maximum current density and the polarization resistance of the electrolyzer. In contrast, a correlation is observed between the physicochemical features of the reduced cathodic catalyst, the iR-free potential and the polarization resistance after prolonged operation. The best-performing Co-free MEA achieved a current density of 0.51 A cm⁻² at 2.2 V and exhibited stable operation for hundreds of hours under alkaline electrolysis conditions. Although the complete replacement of cobalt results in lower activity than previously reported Co-containing HEOs, the present work establishes a viable design strategy for fully Co-free electrocatalysts and highlights the critical balance between catalytic performance, long-term stability, and material sustainability in future AEMWE technologies. Full article

Smart chemical sensors have emerged as promising tools for real-time monitoring of food spoilage in both fermented and non-fermented products. By detecting key spoilage indicators—including biogenic amines, ammonia, hydrogen sulfide, methane, pH variations, and microbial volatile organic compounds (MVOCs)—these systems enable rapid, on-site assessment of food quality, offering a viable alternative to conventional, time-consuming laboratory analyses. Recent advances encompass diverse sensing mechanisms, including chemiresistive platforms based on conducting polymers and MEMS (Microelectromechanical Systems); optical/colorimetric systems using dyes, metal–organic frameworks, and porphyrins; and electrochemical and biosensing approaches employing enzymes, antibodies, aptamers, and whole-cell recognition elements. These sensors demonstrate high sensitivity (ppb–ppm range), enabling early detection of spoilage before sensory perception or microbiological threshold exceedance. Their applicability has been validated across a wide range of food matrices, including meat, fish, dairy products, vegetables, beverages, and fermented foods. Despite significant progress, key challenges persist, including signal drift, limited specificity, susceptibility to environmental factors such as humidity and temperature, and interference from complex food matrices. Furthermore, integration into intelligent packaging requires the development of flexible, food-safe, and regulatory-compliant materials. Emerging approaches that combine sensor arrays with machine learning and MVOC pattern recognition are enhancing predictive accuracy and enabling food classification across commodity types. Overall, smart chemical sensing technologies are rapidly transitioning from laboratory prototypes to practical applications in intelligent packaging and wireless monitoring systems, with ongoing research focused on improving robustness, standardization, and scalability for commercial deployment. This article provides an overview of the topic, drawing on the available bibliography from the last five years and the most-cited scientific databases. Full article

The electrochemical regeneration of sodium borohydride (NaBH₄) from spent metaborate is a central bottleneck for circular hydrogen storage. (1) Background: The eight-electron reduction of the aqueous borate species B(OH)₄⁻ to BH₄⁻ is thermodynamically out-competed by the hydrogen-evolution reaction (HER) by about 0.41 V at every pH, so selectivity can only be won kinetically. (2) Methods: We advance an ambiphilic-site hypothesis, screen 30 candidate metal centres using entirely experimental, tabulated descriptors (bulk HER exchange current density; gas-phase M-O bond energy) with no new electronic-structure computation, and then audit the transferability of both descriptor axes against published, corrected DFT datasets for nitrogen-coordinated single-atom sites. (3) Results: At the parent-metal level, the two axes are orthogonal (Spearman ρ = 0.02) and the score passes a family-level experimental validation over seven bulk-electrode metals (ρ = 0.69; exact permutation p = 0.050), separating the HER-dominated noble-metal family from the single-atom Mn benchmark. The site-level audit shows that the oxophilicity axis transfers to M-N₄ sites almost quantitatively (ρ = −0.84 pyridine-4N, −0.95 pyrrole-4N, n = 23) while the bulk HER axis does not, and that site-level scaling between oxygen and hydrogen binding narrows the productive window to oxophilic centres that over-bind hydrogen. (4) Conclusions: The site-anchored screen redirects the search from the parent-metal leaders (La, Ce, Y, Ti, Sc) to refractory single-atom centres, with W, Nb and Mo as priority synthesis targets (Re excluded on scarcity; Zr, Hf, Ta as data-supported extensions; Ti as the sustainability-anchored borderline case) and the lanthanides retained only as explicitly extrapolative candidates. All data and analysis code are openly deposited. Full article

Electrochemical CO₂ reduction reaction (eCO₂RR) is a promising technology for carbon utilization, yet achieving high product selectivity and long-term stability remains a critical challenge. In this study, we investigated the performance and surface stability of Cu electrodes modified with Ag nanoparticles using a spray-coating method. While a bare Cu reference electrode exhibited an initial starting period dominated by hydrogen evolution before shifting toward hydrocarbon production after two hours, the Ag-spray-coated Cu electrode demonstrated immediate and stable catalytic activity. Electrode potential remained stable throughout the 12 h evaluation, in contrast to the negative shifts observed with the bare Cu electrode. Ambient pressure hard X-ray photoelectron spectroscopy (AP-HAXPES) revealed that while the bare Cu surface remained metallic, the Ag-spray-coated Cu surface existed as Cu₂O during the reaction. The enhanced selectivity and stability are attributed to a spillover mechanism, where CO generated on the Ag nanoparticles migrates to adjacent Cu₂O sites, inhibiting hydrogen evolution and facilitating efficient reduction to methane and ethylene from the onset of electrolysis. These findings demonstrate that surface modification via nanoparticle spray coating is a highly effective strategy for achieving selective and stable CO₂ conversion on bimetallic catalysts. Full article

Hydrogen produced through electrochemical water splitting is considered one of the most promising energy carriers for achieving a sustainable and carbon-neutral future. However, the practical implementation of water electrolysis remains limited by the sluggish kinetics of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), as well as the high cost and limited availability of conventional noble-metal catalysts. Single-atom catalysts (SACs), which feature isolated metal atoms anchored on suitable supports, have emerged as an attractive class of electrocatalysts owing to their nearly complete atomic utilization, well-defined active sites, and tunable electronic structures. This review provides a comprehensive overview of recent advances in SACs for electrochemical water splitting. The fundamental mechanisms of HER and OER are first discussed, followed by the influence of the unique electronic structure, coordination environment, and metal–support interactions on catalytic performance. Various bottom-up and top-down synthesis strategies, together with advanced characterization techniques for identifying atomically dispersed active sites and elucidating structure–activity relationships, are systematically summarized. Furthermore, recent progress in noble-metal, non-noble-metal, and dual-atom catalysts is critically reviewed, with emphasis on their roles in regulating electronic structure, reaction intermediate adsorption, catalytic activity, HER/OER kinetics, and long-term stability. Finally, the remaining challenges and future perspectives for the scalable and practical application of SACs in water electrolysis are discussed. Overall, this review highlights the potential of SACs to maximize metal utilization while maintaining high electrocatalytic performance and provides valuable insights for the rational design of next-generation electrocatalysts for sustainable hydrogen production. Full article

Protonic ceramic electrochemical cells (PCECs), including protonic ceramic fuel cells, electrolysis cells and reversible cells, have attracted increasing attention as efficient solid-state devices for electricity generation, hydrogen production and chemical conversion at intermediate temperatures. Recent advances in electrolyte thinning, electrode nanostructuring and interface engineering have enabled remarkable device performance, including reversible operation at 500–650 °C, operation below 450 °C, and expanded fuel flexibility toward hydrogen, ammonia and methane-containing feeds. However, the working-state mechanisms governing their performance and durability remain insufficiently understood. In particular, proton incorporation, surface hydration, proton exchange, proton-coupled oxygen reduction/evolution, electrode reconstruction and buried interface degradation are highly dynamic processes that cannot be fully resolved by ex situ or post-mortem characterization. Operando characterization provides a powerful route to bridge this knowledge gap by directly correlating structural, chemical and electrochemical evolution under realistic temperature, steam, gas atmosphere and electrochemical bias. In this review, we summarize recent progress in operando and in situ characterization of PCECs, with emphasis on vibrational spectroscopy, X-ray-based techniques, neutron methods, electron microscopy and electrochemical diagnostics. We discuss how operando DRIFTS and H/D isotope exchange reveal voltage-dependent proton exchange kinetics, how operando Raman captures oxygen-electrode surface reconstruction, how X-ray and neutron methods probe redox chemistry and proton dynamics, and how EIS/DRT analysis links structural changes to reaction resistance. We further highlight current challenges, including limited access to buried interfaces, difficulty in quantifying protonic defects, insufficient multimodal correlation and the lack of standardized operando cell configurations. Finally, we propose future directions based on isotope-resolved spectroscopy, multimodal operando platforms, AI-assisted spectral/impedance analysis and theory-guided interpretation. This review aims to establish a working-state mechanistic framework for rationally designing durable, high-performance PCECs. Full article

Green hydrogen (H₂) production is a pivotal element of Saudi Arabia’s Vision 2030. This study presents a comprehensive feasibility assessment of a high-efficiency H₂ production system integrating a photovoltaic (PV) array and a high-concentration photovoltaic (HCPV) system with a Proton Exchange Membrane (PEM) electrolyzer, specifically designed for harsh climatic conditions. To evaluate the system’s viability, a comprehensive simulation model was developed based on rigorously validated mathematical formulations. First, the performance of the PEM electrolyzer and the effectiveness of the cooling system were modeled using established electrochemical and thermal correlations derived from the peer-reviewed literature. Second, this model was applied to evaluate the system’s long-term energy yield and economic performance. Key economic metrics, including the levelized cost of H₂ (LCOH) and discounted payback period (DPBP), were calculated based on local solar irradiance data, followed by a sensitivity analysis to assess the economic robustness under varying market conditions. The results demonstrate that the proposed configuration is not only technically feasible—maintaining high efficiency despite harsh environmental conditions—but also economically viable, offering a competitive LCOH and attractive DPBP that align with the strategic objectives of Saudi Vision 2030. Full article

Hydrogen production by alkaline water electrolysis is a promising pathway for sustainable energy systems; however, conventional electrolyzers rely on membranes or diaphragms that increase cost, electrical resistance, and maintenance requirements. This study reports the development and experimental evaluation of a low-cost, membrane-less, flow-by tubular alkaline electrolyzer integrated with a dedicated gas–liquid separation and volumetric gas-measurement system. The electrolyzer was designed, constructed, experimentally validated, and electrochemically characterized using polarization curves. The effects of KOH concentration (0.50–2.00 mol L⁻¹), electrolyte flow rate (1.00–4.00 L min⁻¹), and applied voltage (2.20–3.20 V) on hydrogen production were investigated through a full factorial 3³ experimental design combined with analysis of variance, response surface methodology, and numerical optimization using the desirability function. The applied voltage was identified as the dominant operating variable, followed by KOH concentration and electrolyte flow rate, while significant interactions involving voltage were also observed. The quadratic regression model showed excellent predictive performance (R² = 0.9614), and within the investigated operating domain, the highest hydrogen production rate was obtained at 2.00 mol L⁻¹ KOH, 1.00 L min⁻¹ electrolyte flow rate, and 3.20 V, resulting in an experimental hydrogen production rate of 0.4395 mL s⁻¹. These findings demonstrate the potential of the proposed membrane-less flow-by electrolyzer as a simplified, low-cost, and experimentally validated platform for investigating and optimizing membrane-less alkaline water electrolysis under the evaluated operating conditions. Full article

Reactive oxygen species (ROS) regulate cellular signaling at physiological concentrations and drive tissue damage when their generation exceeds antioxidant defenses. The conceptual reframing of the field into oxidative eustress (low, controlled redox signaling) and oxidative distress (supraphysiological levels causing biomolecular damage), alongside parallel advances in detection chemistry and genetically encoded biosensors, has transformed how investigators measure ROS in living systems. This review provides a critical, methods-focused update covering the contemporary toolkit, with particular emphasis on advances from 2015 to 2026 while incorporating earlier foundational work where it remains indispensable to interpretation. Consistent with the title and reflecting both the maturity of the available chemistry and the weight of the recent literature, our emphasis falls on hydrogen peroxide and mammalian experimental systems; superoxide, the hydroxyl radical, and singlet oxygen are addressed primarily where their detection intersects with the platforms reviewed here, and non-mammalian models are considered only selectively. Readers seeking dedicated coverage of these other species or of plant, microbial, and invertebrate systems are directed to the specialized reviews cited throughout. Five complementary measurement platforms are evaluated: (i) electron paramagnetic resonance spectroscopy with classical nitrone spin traps and the newer cyclic hydroxylamine probes; (ii) small-molecule fluorescent probes, with particular emphasis on the boronate-based, activity-based sensing platform that has supplanted 2′,7′-dichlorofluorescin diacetate for hydrogen peroxide imaging; (iii) genetically encoded biosensors of the HyPer and roGFP families, which now permit ratiometric, organelle-resolved, and longitudinal measurements; (iv) mass-spectrometry-based quantification of oxidation products and radical adducts, including isoprostanes, 2-hydroxyethidium, and redox-modified cysteines via chemical proteomics; and (v) electrochemical and nanosensor approaches enabling real-time single-cell measurements. The selectivity, sensitivity, temporal resolution, spatial resolution, and quantitative capability of each platform are critically compared. Reliance on a single non-specific probe is no longer sufficient as the sole evidence base for quantitative or species-specific claims; contemporary investigators are expected to apply complementary approaches and to validate findings across modalities. Standardization of reporting, integration with single-cell omics, and clinical translation of validated mass-spectrometry biomarkers are identified as priorities for the coming decade. Full article