Alkaline electrolyte interphase exchange membrane (PEM) electrolysis, solid oxide electrolyzer (SOEC), photocatalytic water splitting, methane pyrolysis, bio-stimulated hydrogen, naturally occurring hydrogen: a turning point for the hydrogen energy industry?
While prioritizing energy security over sustainability has slowed the momentum of low-carbon hydrogen development, the International Energy Agency (IEA) projects that the reserve for low-carbon hydrogen projects will reach approximately $8 billion by 2025, almost double that of 2024.
Analysts at PV Tech Research predict that green hydrogen will grow at an annual rate of 200% in Europe alone, with over 60 projects currently under construction. Microsoft's seven-year agreement with a green hydrogen company to use green hydrogen to produce steel for data centers suggests a potential surge in demand for green hydrogen from industries struggling to reduce emissions. Meanwhile, markets like the EU are increasing policy support (link to Joao's article for PEI, forthcoming), and technology is advancing.
Many sustainable production methods are still in the experimental or demonstration phase; which methods are most promising and worth watching?
Alkaline Electrolysis
Steam methane reforming (also known as grey hydrogen) remains the most widely used method for hydrogen production, accounting for 68% of global output, but emitting up to 12 kg of carbon dioxide per kilogram of hydrogen produced. Water electrolysis, considered "green" hydrogen production if using renewable energy, accounts for only 5%.
Of these methods, alkaline electrolysis is the most mature and widely used. It consists of two electrodes-an anode and a cathode-separated by a porous membrane. An alkaline solution surrounds the electrodes. When electricity is applied, water molecules separate at the negatively charged cathode, releasing hydrogen gas. This is a low-temperature electrolysis technology, typically operating at 50-80°C. While inexpensive, it is less sensitive to power fluctuations common when using renewable energy.
Proton Exchange Membrane (PEM) Electrolysis
Proton exchange membrane (PEM) electrolysis uses a similar low-temperature technology but replaces the membrane with a polymer membrane. This improves conductivity and gas tightness, making it more efficient than alkaline electrolyzers. PEM electrolyzers are less affected by power fluctuations than alkaline electrolyzers, but currently rely on platinum and iridium, two of the rarest elements in the world.
Solid Oxide Electrolyzers (SOECs)
Solid oxide electrolyzers (SOECs) have attracted considerable attention in recent years. They employ the same electrolysis process but require higher temperatures, between 600°C and 1000°C, and use ceramic membranes. Therefore, SOEC efficiencies can reach up to 85%, and Mitsubishi Heavy Industries (MHI) aims to increase the efficiency of its SOEC units to 90%, far exceeding the efficiencies of alkaline and proton exchange membrane (PEM) electrolyzers. SOECs originate from solid oxide fuel cells, a mature technology requiring only small amounts of rare metals.
Photocatalytic Water Splitting
As the name suggests, photocatalytic water splitting uses light energy to drive the electrolysis of water, with nanoparticles called spinel-type ferrites acting as catalysts. Due to their magnetic properties, they are easily recycled and reused. This process uses abundant materials such as iron, which promises to significantly reduce costs as the technology moves from academia to practical applications. Methane Pyrolysis
Mitsubishi Heavy Industries (MHI) is also developing methane pyrolysis technology to produce "blue-green hydrogen" by decomposing natural gas into solid carbon and hydrogen. MHI is working to improve the hydrogen production efficiency of this process. The carbon black produced can be used as an industrial material.
Biostimulated Hydrogen
In addition to numerous chemical methods, researchers are also exploring biological solutions-using microorganisms in depleted oil fields to convert residual petroleum into hydrogen. A recent field trial in California successfully produced hydrogen using this method.
Naturally Occurring Hydrogen
To date, synthesis has been the primary method for hydrogen production, but the Earth's crust also contains abundant natural hydrogen (or "white hydrogen") resources. An oil well in Mali has been producing natural hydrogen since 2012, and significant reserves have since been discovered in other parts of the world. The U.S. Geological Survey estimates that if 2% of the world's natural hydrogen resources could be sustainably extracted, approximately 100,000 tons of hydrogen could be produced-equivalent to twice the energy of all natural gas reserves.
A Turning Point for the Hydrogen Industry?
Despite some challenges, low-carbon hydrogen energy has entered a crucial stage of development, with the number of announced projects and policy support continuing to grow. Whether hydrogen energy can further become a major decarbonization pathway will depend on the establishment of a more predictable and sustainable policy framework to promote demand growth and attract investors, as well as the ability of technology providers to commercialize and scale up various solutions.
