Abid Ullah

Hydrogen energy has emerged as one of the most promising pathways for achieving sustainable, low-carbon, and net-zero energy systems in response to growing concerns regarding climate change, greenhouse gas emissions, and fossil fuel depletion. Owing to its high energy density, environmental compatibility, and versatility across multiple sectors, hydrogen is increasingly recognized as a key energy carrier for future clean energy infrastructures. In particular, hydrogen fuel cells and electrochemical conversion technologies offer highly efficient alternatives to conventional combustion-based systems while enabling significant reductions in carbon emissions across transportation, power generation, industrial manufacturing, and renewable energy integration. This review provides a comprehensive overview of recent advances in hydrogen energy and fuel cell technologies, focusing on material innovations, electrochemical mechanisms, durability, and sustainable applications. State-of-the-art hydrogen production pathways, including water electrolysis, photoelectrochemical hydrogen generation, thermochemical conversion, and biomass-assisted processes, are critically discussed together with emerging hydrogen storage and transportation technologies. Recent developments in advanced electrocatalysts, including noble-metal-free catalysts, high-entropy materials, perovskite oxides, MXene-derived catalysts, single-atom catalysts, and defect-engineered nanostructures, are evaluated in terms of catalytic activity, electronic structure modulation, stability, and scalability. The review further examines the fundamental electrochemical mechanisms governing hydrogen evolution, oxygen evolution, oxygen reduction reactions, proton transport, and oxygen-ion conduction in fuel cell systems. Various fuel cell technologies, including proton exchange membrane fuel cells, solid oxide fuel cells, proton ceramic fuel cells, and anion exchange membrane fuel cells, are comparatively analyzed with respect to operating principles, electrochemical performance, efficiency, degradation behavior, and commercial readiness. In addition, critical degradation pathways involving catalyst dissolution, carbon corrosion, electrolyte instability, and thermal degradation are discussed together with advanced durability enhancement strategies. Beyond materials and electrochemical perspectives, this review highlights sustainable applications of hydrogen technologies in fuel cell electric vehicles, heavy-duty transportation, stationary power generation, industrial decarbonization, and renewable energy storage systems. Techno-economic feasibility, lifecycle sustainability, carbon footprint analysis, infrastructure development, and global hydrogen market trends are also critically assessed. Finally, emerging future directions involving artificial intelligence-assisted materials discovery, digital hydrogen systems, integrated renewable hydrogen infrastructures, low-cost electrolyzers, and advanced hydrogen storage technologies are outlined to provide strategic insights into the future development of sustainable hydrogen economies and next-generation fuel cell technologies.

Hierarchical titanium dioxide (TiO₂) has emerged as a promising photocatalytic material owing to its excellent chemical stability, environmental benignity, low cost, and high density of surface-active sites. Nevertheless, its practical application is constrained by rapid photogenerated charge-carrier recombination and poor visible-light utilization resulting from its wide bandgap. In the present study, a hierarchical TiO₂/CdS quantum dot (QD) nanocomposite was engineered through a facile and cost-effective pseudo-successive ionic layer adsorption and reaction (p-SILAR) technique with controlled CdS QD deposition. The structural, morphological, optical, and electrochemical properties of the synthesized photocatalysts were systematically investigated using SEM, TEM, XRD, XPS, UV-Vis spectroscopy, photoluminescence (PL), and electrochemical impedance spectroscopy (EIS). The results confirmed the successful deposition of highly dispersed CdS QDs onto the hierarchical TiO₂ framework without altering its morphology or crystal structure. The formation of the heterojunction significantly enhanced visible-light absorption and reduced the optical bandgap from 3.19 eV for pristine TiO₂ to 2.37 eV for the TiO₂/CdS QD nanocomposite. Furthermore, PL and EIS analyses demonstrated suppressed electron–hole recombination and improved interfacial charge-transfer characteristics, respectively. Owing to these synergistic effects, the optimized TiO₂/CdS QD photocatalyst achieved 85.3% degradation of methylene blue under visible-light irradiation within 120 min, exhibiting substantially superior performance to pristine hierarchical TiO₂. Radical scavenging experiments revealed that superoxide radicals ^●O₂⁻ and photogenerated holes (h⁺) were the dominant reactive species governing the degradation process. The enhanced photocatalytic activity is attributed to the combined effects of efficient visible-light harvesting, accelerated charge separation, and effective interfacial charge migration across the TiO₂/CdS QD nanocomposite. These findings highlight the potential of hierarchically structured TiO₂/CdS QD nanocomposites as efficient and economically viable photocatalysts for environmental remediation and wastewater treatment applications.

This chapter explores the sustainability, environmental impacts, and potential solutions to the critical challenges faced by direct liquid fuel cells (DLFCs). A thorough discussion on DLFC utilization patterns, supported by life cycle assessment (LCA), highlights their role in fostering better development practices and environmental stewardship. The chapter also examines the evaluation of fuel cell systems through thermodynamic principles, particularly exergy analysis, emphasizing its utility in enhancing system performance. A detailed review of the present and future of DLFC systems is provided from exegetic, LCA, sustainability, and environmental perspectives. The chapter critically evaluates the ecological impacts, economic viability, and performance of DLFCs, offering a comprehensive analysis of their contribution to environmental and sustainability goals. It also delves into various types of liquid fuels derived from sustainable materials, including biomass, and outlines renewable fuel generation methods powered by solar, wind, geothermal, and hydroelectric energy sources. By addressing the significance of DLFC technology, this chapter aims to inspire researchers, engineers, scientists, and policymakers worldwide to advance liquid fuel cell systems for a sustainable future.

The development of direct formic acid fuel cells (DFAFCs) as a potential source of energy to meet the escalating demand for portable electronic devices. These fuel cells hold particular significance due to their notable attributes, including high electromotive force with a theoretical open circuit potential of 1.48 V, restricted fuel crossover, and commendable power densities achievable at low operating temperatures. This chapter endeavors to provide a comprehensive overview of the key components influencing DFAFC performance, primarily focusing on catalysts, membranes, and recent advancements in the field. Platinum-based catalysts, renowned for their proficiency in formic acid oxidation, have a rich history of application in DFAFCs. These catalysts are essential in facilitating the anodic reaction such that significantly impact overall cell efficiency. Understanding the nuances of catalyst design, synthesis techniques, and structural modifications is paramount for enhancing DFAFC performance. Exploration of alternative catalyst materials and formulations has also gained traction, seeking to mitigate the cost and scarcity associated with platinum, while concurrently optimizing ability and catalytic activity. Additionally, to catalysts, the selection and design of appropriate membranes are crucial considerations in DFAFC development. Membranes serve as the electrolyte separator, influencing ion conductivity and ensuring effective separation between the anode and cathode compartments. This chapter delves into the diverse range of membrane materials, their ion exchange properties, and their compatibility with the unique operational requirements of DFAFCs. By presenting a comprehensive analysis of catalysts, membranes, and the latest strides in DFAFC research, this work aims to foster a deeper understanding of the intricate interrelationships within these fuel cell systems.

In the field of fuel cell technology, the development of cost-effective catalysts is crucial for the commercialization of Alkaline Membrane Fuel Cells (AMFCs). Platinum (Pt) has traditionally been employed as the catalyst in AMFCs, but its high cost poses a major barrier to widespread adoption. In this study, a new catalyst material was developed by incorporating Manganese Dioxide (α-MnO₂) into Carbon Nanotubes (CNTs) using hydrothermal synthesis techniques. The synthesized catalyst was characterized using Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD), and its electrocatalytic activity was evaluated through Linear Sweep Voltammetry (LSV) and CV through Rotating Disc Electrode (RDE) experiments. The results showed that the α-MnO₂-CNT composite displayed strong durability in the alkaline environment and high electrocatalytic activity for oxygen reduction reaction (ORR). The LSV measurements revealed a current density of -4.1 mA/cm² and an overpotential of -0.3V relative to Standard Calomel Electrode (SCE) in a 0.1M KOH electrolyte. Additionally, the α-MnO₂-CNT composite displayed high methanol tolerance and long-term stability compared to commercial Pt/C catalysts. This study demonstrates that the use of α-MnO₂-CNT as a cost-effective alternative to Pt has the potential to facilitate the commercialization of AMFC technology.

Recently, a tremendous upsurge in the research of Solid oxide fuel cells (SOFCs) has been documented due to cheap electricity production and without harming the environment. The development of efficient SOFCs requires more robust cathode for oxygen reduction. Until yet a copious amount of research has been done on varieties of materials including LSCF. In this work, Ruthenium is doped on the LSCF forming nanostructured Ru-LSCF with various Ru stoichiometric quantities. The Ru-LSCF catalyst is prepared via simplistic technique “Glycine combustion process”, producing evenly embedded Ru in LSCF perovskite materials leading to increased oxygen reduction reaction (ORR). The nanostructured Ru-LSCF cathode showed polarization resistance of approximately 0.031 Ωm² at 750 ⁰C. The peak powers of approximately 1760.5, 1480.1, 893.3 mW/cm² were recorded at 750, 700, and 650 ⁰C, respectively. Ru LSCF was quantitatively optimized for enhanced power production with high precision calculation. The results show that the Ru-LSCF optimum fabricated nanostructured cathode is promising catalyst for the reduction of oxygen at the cathode side for highly durable SOFCs.

Polymer Electrolyte Membrane Fuel Cell (PEMFC), an electrochemical power generating technology, uses a precious metal Platinum (Pt) catalyst for Oxygen Reduction Reaction (ORR), which is a major hindrance in its commercialization. Using a non-precious group metal (NPGM) instead of Pt will reduces the cost of PEMFCs. Herein MnO2 carbon nanotubes (CNTs) were synthesized by impregnating the transition metal in large surface carbonaceous material CNTs by hydrothermal synthesis techniques. To enhance the catalytic reaction and increase the volumetric current density, the sample was pyrolyzed at 800 0C temperature under nitrogen atmosphere. During pyrolysis, the nitrogen was also doped in the framework of carbonaceous materials. The materials were then treated with acid, removing the unreacted metals and adding oxygen functional group to the CNT framework due to which the activity of the catalyst is amplified. The catalysts have been characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), Catalyst activity has been calculated by Rotating Disc Electrode (RDE) experiment. The resulting materials are stronger in experimental conditions in alkaline environment and have high electro catalytic activity for oxygen reduction reaction (ORR). Linear Sweep Voltammetry (LSV) depicts a current density of - 4.0 mA/cm2 and over potential of -0.3V vs. Standard Calomel Electrode (SCE) in 0.1M KOH electrolyte. Rotating Disk Electrode (RDE) was conducted at 400, 800, 1200, and 1600 rpm. The results of MnO2CNT show a desirable future aspect in fuel cell commercialization.

A highly active Platinum Group Metal (PGM) and non-PGM electrocatalysts with thermally extruded nanotubes have been prepared for Proton Exchange Membrane (PEM) fuel cell by sintering Nickel zeolitic imidazole framework (Ni-ZIF). Preeminent electro-catalytic activities have been observed through single fuel cell tests and rotating disk electrode (RDE). This study involves the comparison of Oxygen Reduction Reaction (ORR) activities and fuel cell (FC) test station performance of two catalyst Nickel and Platinum mixed Nickel nanotubes (Ni NT, Ni/Pt NT) respectively. The acidic cells with corresponding Ni and Ni/Pt catalysts delivers peak power densities of 325 mWcm^-2 and 455 mWcm^-2 at 75 °C inside fuel cell. Our results indicate that, the synthesized Nickel nanotubes has profound effect on catalytic performance of both PGM and non-PGM electro catalysts.

In this study, pristine MnO₂ catalyst was synthesized by hydrothermal technique and annealed at 400 and 600°C (MnO₂@400°C and MnO₂@600°C) transforming it into nanorods in a nitrogen atmosphere. The heat treatment process ameliorates the catalytic activity of the MnO₂ catalyst by inducing oxygen vacancies. The catalyst is characterized by scanning electron microscope, and X‐ray diffraction, Fourier transforms infrared spectroscopy (FTIR), Electron paramagnetic resonance (EPR), and X‐ray Photoelectron Spectroscopy, whereas the oxygen reduction reaction (ORR) activity examined through rotating disc electrode and fuel cell test station. To elucidate the effect of sintering temperature on the MnO₂ nanorods, the high angle annular dark‐field (HAADF) imaging was carried out on the samples. MnO₂@400°C showed preeminent robustness to withstand austere alkaline environment during the experiment and possessed high electrocatalytic activity for the ORR with current density and onset potential values of 6.4 mA cm^–2 and 0.80 V VS (RHE), respectively. The single‐cell test experiment of alkaline fuel cell delivered peak power density 81 mW/cm at 50°C. It is believed that this idiosyncratic behavior of MnO₂ nanorods is due to the preferential growth on (211) and (310) indices and coexistence of optimized Mn⁴⁺/Mn³⁺ oxidation states as well as the creation of optimum oxygen vacancies on MnO₂ nanorods. Moreover, the stretching of MnO₂ nanorods occurs with increasing temperature and thus increasing the surface area to volume ratio. Thus thermal treatment shows that MnO₂ is highly sensitive toward temperature variation and optimum ORR results can be obtained at adequate temperatures.