The demand for clean hydrogen is escalating as it is crucial for processes that cannot solely rely on renewable electricity. Innovative methods are emerging to generate substantial amounts of hydrogen from underground rocks while effectively sequestering carbon dioxide.

Researchers from the University of Texas at Austin have validated this hydrogen production process using common rock types in laboratory settings. They are actively seeking partnerships with industry players to launch demonstration experiments.

“Our goal is to prove that hydrogen can be produced economically while simultaneously capturing CO2,” states Orsolya Gerensel. She also mentions the potential for concurrent geothermal energy generation.

Hydrogen combustion results in only water vapor, making it a clean energy source that can significantly contribute to achieving net-zero emissions. It is particularly valuable for decarbonizing industrial processes like fertilizer and steel production.

However, the current majorities of hydrogen production stem from fossil fuels, which release considerable CO2. Transitioning to renewable methods, like using wind or solar power to split water, can mitigate these emissions.

Although the use of renewable energy for hydrogen production is gaining traction, current costs remain high, and large-scale production requires massive amounts of green energy, limiting its availability for other critical areas like phasing out coal plants.

This has sparked renewed interest in natural hydrogen from geological sources. Various processes can generate hydrogen in sedimentary rocks, and under optimal conditions, it can be extracted similarly to natural gas. While some researchers are optimistic about abundant natural hydrogen reserves, others, including Gerensel, express caution about its potential limitations.

Presently, the village of Bourakebugou in Mali is the only known location extracting nearly pure natural hydrogen, albeit on a small scale.

“This is a unique situation,” Gerensel explains. Due to typically low hydrogen production rates and the challenge of accumulating it beneath impermeable rocks, large-scale natural deposits are rare.

To overcome this, many teams worldwide are researching ways to artificially stimulate hydrogen production from rocks. This method is termed stimulated hydrogen generation, and various trial techniques are already in progress.

One approach involves pumping groundwater. When water interacts with specific rock types, it produces hydrogen through a process known as serpentinization, offering a substantial hydrogen source. Increasing water flow can further accelerate this process.

Gerensel and her research team found that adding CO2 to the water could enhance the reaction with rocks, sequestering the carbon in the form of carbonates. A firm named Carbfix is already mineralizing CO2 in Iceland by injecting it into water at geothermal plants.

In their lab tests using iron-rich volcanic rock, the team replicated deep subsurface conditions by heating rock samples to 90 degrees Celsius under pressure, supplementing with water containing CO2 or an inert gas. The results indicated that CO2-rich water released more hydrogen, likely due to the formation of carbonic acid that promotes rock dissolution, thus enhancing the hydrogen production reaction. Furthermore, the addition of nickel chloride as a catalyst significantly boosted production, Gerensel shared at a recent European Geosciences Union meeting in Vienna.

Theoretically, they could release about 0.5 percent hydrogen from the water-rock reaction, though achieving 1% efficiency is necessary for economic viability. One strategy to improve this is by drilling deeper into high-temperature areas to foster serpentinization, even if it raises costs. The potential exists to utilize higher temperatures for geothermal power generation.

Vast deposits of iron-rich rocks exist globally, and even achieving just 1% efficiency could yield significantly more hydrogen than the current annual global production of 100 million tons.

“Good work” praises Barbara Sherwood Lollar from the University of Toronto.

“Interest is clearly rising in strategies that link stimulated geological hydrogen production with CO2 mineralization,” comments Aliaksey Patnia from the University of Oxford, UK. “Numerous groups and startups are probing various adaptations of this concept.”

If firms can sequester CO2 effectively, as Carbfix does, they can enhance project viability and attract investors through potential revenue streams. Nonetheless, the practical feasibility of either method remains to be evaluated.

Sherwood Lollar argues for a deeper exploration of stimulated hydrogen production techniques beyond relying solely on known natural reserves. Her team discovered that a mine in Timmins, Ontario, emits about 140 tons of hydrogen annually, presenting local exploitation opportunities.

“There isn’t a single answer,” she asserts. “Multiple potential strategies must be explored and expedited.”