The global quest for a sustainable energy future hinges significantly on the widespread adoption of hydrogen, a clean energy carrier often lauded as "the fuel of the future." Its potential to decarbonize vast sectors of the global economy is immense. When burned or utilized in fuel cells, hydrogen produces only water as a byproduct, offering a clean energy source. Furthermore, it can serve as a direct replacement for fossil fuels in many applications and act as a crucial chemical feedstock for industries that are notoriously difficult to decarbonize, such as steel and cement production. However, realizing this ambitious vision requires overcoming substantial hurdles, with two primary challenges demanding urgent attention: the cost-effective and low-carbon production of pure hydrogen, and the equally critical, yet often less discussed, issue of its efficient transportation and storage.
A team led by researchers at the MIT Energy Initiative (MITEI), in collaboration with ExxonMobil Technology and Engineering Co., has been diligently tackling the latter challenge. Their work addresses the fundamental problem that the optimal locations for hydrogen production are likely to be geographically distant from its points of consumption, necessitating robust and scalable transportation solutions. The inherent properties of hydrogen gas—its extreme lightness and low energy density by volume—pose significant logistical difficulties. Delivering a substantial amount of energy via hydrogen requires a considerable volume of the gas, demanding exceptionally well-sealed containment systems to prevent the minuscule hydrogen molecules from escaping. This contrasts sharply with the relative ease of transporting liquid fuels like gasoline. Without effective means of storing and transporting hydrogen, its promise as a cornerstone of a clean energy economy remains unfulfilled.
Addressing the Transportation Conundrum: The Genesis of HyCAT
The research initiative, funded by ExxonMobil Technology and Engineering Co. through MITEI, commenced in 2024. The multidisciplinary team, comprising MITEI researchers and their Exxon colleagues, embarked on a comprehensive examination of various hydrogen transportation methodologies. Their findings underscored a crucial realization: there is no universal "one-size-fits-all" solution. The economic viability and carbon footprint associated with any given transportation method are intrinsically linked to specific geographical contexts and local conditions. Rather than attempting to present a definitive ranking of "best" outcomes, the researchers developed an innovative analytical tool designed to empower users to navigate these complexities and select the most appropriate method for their unique use cases.
This groundbreaking study and the accompanying analytical tool are detailed in a recent paper published in the esteemed journal Fuel. The research was spearheaded by former MITEI postdocs Gasim Ibrahim, now an R&D Engineer/Scientist at Honeywell, and Guiyan Zang, a former MITEI group lead who has since become an Associate Professor at Washington State University. Several other MIT researchers contributed significantly to the project, including former postdocs Bosong Lin, Jacqueline Garrido, Woojae Shin, and Haoxiang Lai.
The Hydrogen Challenge and the Role of "Carriers"
The foundational assumption guiding the research was the necessity for hydrogen to be transported over long distances—across continents, oceans, or vast bodies of water—to achieve its global potential as a viable fuel. Given hydrogen’s gaseous nature, converting it into a liquid form prior to shipment emerged as the most practical strategy. The central questions then became: what are the most effective methods for achieving this conversion and subsequent transport, what are the associated costs, and how do these methods impact the carbon intensity of the delivered hydrogen?
"There hasn’t been a lot of attention paid to addressing those questions," noted Ibrahim in an interview, highlighting a significant gap in existing research. While some studies have explored these issues, their conclusions have often been inconsistent, and many uncertainties persist. These uncertainties stem from the inherent variability of costs and carbon emissions from place to place, compounded by a lack of extensive data on the practicalities of large-scale hydrogen transportation.
"So we decided the best thing to do was to develop an adaptive tool that would enable users to perform their own assessments—a tool that could be updated very easily," Ibrahim explained. "And we would make it open source, so anyone can see and update the numbers that we used in formulating and testing it. As the industry develops, and as scale becomes more a factor, the assumptions made in [our initial] assessments of the economics and the carbon intensity [of different shipping methods] will need to be updated."
To maintain a focused analysis on transportation and storage, the developed model, christened the Hydrogen Carrier Analysis Tool (HyCAT), deliberately excludes the upstream processes of hydrogen production and the downstream applications of its use. HyCAT’s core function is to quantify the costs and greenhouse gas (GHG) emissions incurred during the hydrogen’s journey from its point of origin to its point of delivery. While a comprehensive life-cycle assessment would encompass all environmental impacts, HyCAT zeroes in on GHG emissions as a primary metric.
Ibrahim described the tool as user-friendly, featuring an intuitive interface with drop-down menus for inputting assumptions. The analytical results are presented in clear bar charts, with accompanying links to detailed tables for deeper dives into the data.
He further clarified that although HyCAT operates within a well-defined boundary—"incoming hydrogen to outgoing hydrogen"—users are required to input specific local factors relevant to their situation. These inputs include the carbon intensity and cost associated with the production of the incoming hydrogen. "So that will inform the final values that come out of a HyCAT analysis," Ibrahim stated, explaining why the tool generates location-specific results.
Based on user-defined assumptions, HyCAT meticulously calculates the costs and GHG emissions across five critical stages of the hydrogen supply chain:
- Liquefaction/Conversion: The energy and emissions associated with transforming gaseous hydrogen into a transportable form.
- Storage: The costs and emissions related to storing the hydrogen at the production site before shipment.
- Shipping/Transport: The primary logistics phase, accounting for the energy consumed and emissions generated during transit.
- Regasification/Reconversion: The energy and emissions required to convert the hydrogen back into its usable gaseous state at the destination.
- Storage at Destination: The costs and emissions associated with storing the hydrogen after it arrives.
Exploring Liquefaction and Carrier Options
A pivotal decision in any hydrogen transportation plan revolves around how to convert the gaseous hydrogen into a liquid or a carrier compound, and subsequently, how to recover the hydrogen gas at the destination.
One direct approach involves liquefying gaseous hydrogen. However, this process demands extreme sub-zero temperatures. "You would need to consume about a third of the energy content of the hydrogen to make the gaseous hydrogen cold enough to liquefy," Ibrahim noted. A further challenge arises from the potential for the liquefied hydrogen to re-gasify and escape during storage and transit if the containment vessels are not adequately insulated. The primary advantage of liquefaction is that it does not involve chemical reactions.
An alternative strategy employs hydrogen "carriers." These are liquid chemical compounds capable of absorbing hydrogen atoms under specific conditions and releasing them under others. This method transforms the transportation problem into one of moving a liquid chemical compound that carries hydrogen. The process inherently involves two chemical reactions: one to bind the hydrogen to the carrier and another to release it at the point of use.
In their analytical demonstrations, the researchers evaluated three potential carrier compounds, each possessing distinct advantages and disadvantages:
Toluene-Based Carriers
One investigated carrier is derived from toluene, a hydrocarbon. While the chemical reaction of adding hydrogen to toluene is not extensively studied, a significant drawback is the typical origin of toluene from the oil and gas industry, resulting in a relatively high initial carbon intensity. Furthermore, some toluene is inevitably lost over time, necessitating periodic replenishment.
Synthetic Methane
The researchers also examined "synthetic methane," produced by reacting hydrogen with carbon dioxide (CO2). This reaction is well-established, and a notable benefit is that it consumes CO2, often captured from the atmosphere, thus offering a carbon sequestration component. However, a byproduct of this reaction is water, which leads to a loss of some hydrogen with each reaction cycle.
Ammonia
The third option analyzed is ammonia (NH3), formed by reacting hydrogen with nitrogen from the air. This reaction is extensively studied and is already employed commercially for ammonia production. "We’ve been producing ammonia for a long time," Ibrahim stated, emphasizing the availability of existing infrastructure for its transportation and storage. Ibrahim regards ammonia as a "most promising option," though he points out that the reaction required to release the hydrogen from ammonia has not yet received substantial research attention.
Varying Conclusions and Future Outlook
The sample runs conducted using HyCAT revealed a consistent theme: the optimal transportation pathway is highly dependent on specific circumstances. "As we developed the tool, we saw that the ‘best’ carrier was very specific to the supply chain at hand," Ibrahim observed. "It’s a function of how far you’re trying to ship your hydrogen, energy and shipping costs at your exporting and importing countries, the capital cost of building the needed facilities at both ends, and more."
Ibrahim and his team are now planning a follow-up study that will leverage HyCAT to analyze specific supply chains under a range of defined conditions. This next phase will involve identifying assumptions with high degrees of uncertainty and exploring the potential range of values for those assumptions. "Then we’ll be able to say, ‘under these conditions, this carrier is better than that one,’ or ‘this carrier is better at cost, but worse at carbon intensity’," Ibrahim explained.
For the immediate future, the primary takeaway from the current study, according to Ibrahim, is that "there’s no conclusion." He cautions decision-makers against generalizing or extrapolating findings from existing literature to their unique operational contexts. Instead, he strongly recommends utilizing HyCAT to thoroughly explore available options. By integrating the tool’s insights with their specific objectives and organizational values, stakeholders can optimize their hydrogen supply chains and accelerate the realization of clean-burning hydrogen as a global energy solution. The development of HyCAT represents a significant step forward in demystifying the complex logistical challenges inherent in deploying hydrogen at scale, paving the way for its widespread adoption and contributing to a more sustainable future.
