Massachusetts Institute of Technology (MIT) engineers have introduced a pioneering solar energy reactor system tailored for the production of green hydrogen. This groundbreaking concept, known as “solar thermochemical hydrogen,” was recently unveiled in the esteemed Solar Energy Journal.
The system, detailed in the MIT team's publication, focuses on harnessing the sun's heat to directly split water molecules for hydrogen production, all while maintaining a remarkable level of efficiency and a minimal environmental footprint, devoid of greenhouse gas emissions.
Despite the existence of other methods for green hydrogen production, the majority of today's hydrogen is still derived from natural gas and fossil fuels, resulting in significant carbon emissions. This process is often referred to as “gray” fuel due to its potential for carbon-neutral utilization but its carbon-intensive production.
In stark contrast, the MIT team's solar thermochemical hydrogen (STCH) system is entirely reliant on solar energy and, notably, free from carbon emissions.
Traditionally, solar energy has exhibited an efficiency rate of approximately 7 percent for hydrogen production. The newly devised MIT system promises to unlock the potential of harnessing up to 40 percent of the sun's heat for the hydrogen generation process. This achievement overcomes past limitations related to low yield and high costs, paving the way for a more economically viable and scalable solution in the journey towards decarbonizing the transportation sector.
Ahmed Ghoniem, the Ronald C. Crane Professor of Mechanical Engineering at MIT, Director of the Center for Energy and Propulsion Research, and the Reacting Gas Dynamics Laboratory, led the study and emphasized the significance of producing affordable green hydrogen. Ghoniem stated, “We're thinking of hydrogen as the fuel of the future, and there's a need to generate it cheaply and at scale. We're trying to achieve the Department of Energy's goal, which is to make green hydrogen by 2030, at $1 per kilogram. To improve the economics, we have to improve the efficiency and make sure most of the solar energy we collect is used in the production of hydrogen.”
Ghoniem was joined by a collaborative team of researchers, including MIT postdoc Aniket Patankar, MIT professor of materials science and engineering Harry Tuller, Xiao-Yu Wu from the University of Waterloo, and Wonjae Choi from Ewha Womans University in South Korea.
The MIT system, while akin to other solar energy designs that utilize sunlight's heat, distinguishes itself through a circular array comprising hundreds of mirrors. These mirrors concentrate and direct collected sunlight toward a central receiving tower. Subsequently, the STCH system captures the heat from the receiver and employs it to separate water molecules, leading to the production of green hydrogen.
This approach deviates from the conventional method, where solar energy generates electricity that, in turn, powers an electrolyzer to split water into hydrogen and oxygen. The MIT system instead leverages solar heat directly for water splitting.
The core of the conceptual STCH system involves a thermochemical process consisting of two key steps. Initially, water vapor encounters a metal, whereby the metal seizes the oxygen from the steam, leaving hydrogen as the byproduct. This oxidation process bears resemblance to the way iron rusts upon contact with water, albeit at a much swifter pace.
Following the separation of hydrogen through solar heat and interaction with the metal, the oxidized metal is reheated within a vacuum. This reverses the rusting process by eliminating oxygen from the metal. Once the oxygen is removed, the metal cools and is subsequently re-exposed to steam, repeating the cycle numerous times.
This pioneering development not only offers a promising avenue for green hydrogen production but also underscores the transformative potential of clean energy solutions in the quest for a sustainable and eco-friendly future.