Hydrogen-Based Energy Systems for Sustainable Transportation

Rising concerns about climate change, the need to innovate and connect diverse energy sectors, and the challenge of energy dependency are boosting global interest in hydrogen-based technologies. The heart of the energy transition towards sustainable solutions is above all the transport sector, responsible for a significant share of global greenhouse gas emissions. Innovation in the transport sector is mainly driven by a combination of technological, economic, and regulatory factors, which aim to reduce environmental impact, improve energy efficiency, and promote the adoption of innovative concepts.

The international government’s momentum is essential to reach the decarbonization target, i.e., climate neutrality by 2050, through the implementation of increasingly stringent emission regulations and the provision of subsidies and incentives for the design, production, and purchase of new technologies for vehicles and refuelling infrastructures.

In this line of reasoning, Gandiglio and Marocco, in [1], highlight all hydrogen-related financing initiatives in Italy, offering an in-depth overview of the activities associated with these projects. Among them, numerous PNRR initiatives are presented, discussing the project proposals on hydrogen production in brownfield areas (52 expected plants by 2026), hydrogen in hard-to-abate sectors, and the construction of hydrogen refuelling stations for roads (48 stations by 2026) and railways (10 lines). In addition, a valuable goal of this paper is to implement connections between existing and planned projects, encourage the development of new initiatives in the whole hydrogen chain, enhance stakeholder interest in hydrogen, and promote collaboration.

Starting from these considerations, the main elements of the hydrogen value chain are analyzed in this Special Issue, namely production, distribution/storage, and use.

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Concerning production, Pizoń et al. [2] analyze a data-driven artificial neural network model for methane steam reforming processes. The model is trained using experimental, interpolated, and theoretical data, with weights assigned to each data type. The feedforward network investigates the output mixture composition based on operating parameters such as temperature, steam-to-methane ratio, nitrogen-to-methane ratio, methane flow, and nickel catalyst mass.

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The distribution/storage field is investigated by Sgambitterra and Pagnotta in [3], where the mechanisms that cause damage to polymers and polymer-based materials used in hydrogen storage and distribution systems are examined. Since these mechanisms are driven by permeability and since hydrogen storage systems operate under high pressure and varying temperatures, understanding how these factors impact polymer integrity is crucial to preventing catastrophic failures and optimizing designs. In this line, this paper investigates distribution and storage solutions for hydrogen, focusing on the physics of permeability and damage mechanisms, and it highlights challenges and limits in designing reliable polymer-based hydrogen systems.

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For hydrogen use, a particular focus is oriented on proton exchange membrane fuel cells (PEMFCs), the most commonly used fuel cells in transport applications. In detail, Wei Liu et al. [4] investigate PEMFC operations at high current densities (up to 6 A/cm²) using perforated metal plates as gas diffusion layers. A three-dimensional computational model (Ansys-CFX) confirms optimal performance near 100% relative humidity and highlights efficient hydration and performance at low stoichiometric flow ratios (between 1.5 and 2). Along with this paper, Muhammad Habib Ur Rehman et al., in [5], evaluate the impact of sulfonated graphene oxide (GOsulf) on Nafion’s transport properties and electrochemical performance. GOsulf enhances water retention, the bound-water fraction, and diffusivity (1.5 × 10⁻⁵ cm²/s at 130 °C). This results in superior proton conductivity (44.9 mS/cm at 30% RH) under harsh conditions, demonstrating improved hydration and functionality.

In addition to the discussion regarding the potential improvements in the main hydrogen chain steps, this Special Issue also focuses on innovative concepts for heavy-duty transport applications. Firstly, Baldinelli et al., in [6], analyze alternatives to diesel for heavy-duty internal combustion engine vehicles, focusing on hydrogen, e-fuels, and biofuels. They present a methodology for well-to-wheel analysis, assessing energy consumption and CO₂ emissions. According to their results, hydrogen can reduce CO₂ emissions by 29% compared to diesel but requires a 40% higher primary energy consumption. An important and present alternative is hydrotreated vegetable oil, which provides a 35% reduction in energy consumption. In this line, but with particular attention on an innovative vision, Fragiacomo et al., in [7], investigate the performance of an SOFC stack, focusing its applications in sustainable mobility sectors like the maritime and aviation industries. Experimental tests at 750 °C achieved 165 W of electrical power (52% efficiency) and 80 W of thermal power (25% efficiency). Their findings highlight SOFCs’ potential for transport systems, addressing multidisciplinary challenges like material durability, system integration, and regulatory standards, with the aim of supporting future heavy-duty applications.

The papers collected in this Special Issue highlight how hydrogen mobility represents a crucial step toward sustainable transportation, offering significant potential to decarbonize this sector. While technical and economic barriers persist, advancements in fuel production, storage, and infrastructure are accelerating its viability. By fostering innovation, hydrogen can play a decisive role in achieving global climate goals, complementing other renewable energy solutions.