Generating Hydrogen from Rocks: A Sustainable Solution for CO2 Storage

To tackle climate change, the demand for clean hydrogen is rising, especially for sectors that renewable electricity cannot power. Innovative methods may enable us to extract substantial hydrogen from deep underground rocks while simultaneously capturing carbon dioxide.

Researchers from the University of Texas at Austin have demonstrated the viability of this process with common rock types in controlled lab settings and are seeking partnerships for practical demonstration projects.

“Our goal is to provide evidence that hydrogen can be produced economically alongside CO2 sequestration,” explains Orsolya Gerensel. Additionally, this approach could generate geothermal energy.

Burning hydrogen solely emits water vapor, eliminating contributions to global warming. Thus, hydrogen has the potential to significantly help achieve net-zero targets by decarbonizing critical industrial processes, such as fertilizer manufacturing and steel production.

Currently, hydrogen is predominantly derived from fossil fuels, which release substantial CO2 emissions during production. A sustainable method involves using renewable energy sources, like wind and solar, to electrolyze water, yielding hydrogen and oxygen.

While this practice is emerging, hydrogen produced via these methods remains costlier and requires significant renewable energy resources—often limiting alternatives for shifting away from coal power.

This increasing need for natural or geological hydrogen has led to renewed interest. Several processes allow for hydrogen production within rocks, and under optimal conditions, the gas can be harnessed similarly to natural gas. This could be a cleaner and cheaper source, although the extent of accessible natural hydrogen remains uncertain. While some experts predict vast reserves, others, including Gerensel, caution that natural hydrogen resources may be finite.

Currently, nearly pure natural hydrogen is extracted in the small village of Bourakebugou in Mali. However, it is produced on a minimal scale.

“This is a unique scenario,” Gerensel states. Due to the typically low hydrogen production rates and the small size of its molecules, suitable overlying rock formations rarely hold hydrogen effectively, she adds.

Hence, numerous teams worldwide are investigating ways to facilitate hydrogen production from rocks directly, a method known as stimulated hydrogen generation, with various trials already in progress.

One approach involves pumping groundwater to react with certain rock types, initiating serpentinization to produce hydrogen—potentially a substantial natural hydrogen source. More water can accelerate this reaction.

Gerensel and her team posited that introducing carbon dioxide into the water will react with rocks, mineralizing into carbonates. The company Carbfix is pioneering this concept in Iceland, where they mineralize CO2 by injecting it into water pumped underground near geothermal energy plants.

Through laboratory tests using iron-rich volcanic rock, Gerensel’s team simulated deep conditions, heating samples and assessing reactions with either CO2-enriched water or inert argon. Results indicated that CO2-laden water produced significantly more hydrogen, likely due to carbonic acid formation which aids rock dissolution and enhances water interaction. The presence of nickel chloride as a catalyst may further boost hydrogen production, as shared at a recent European Geosciences Union meeting in Vienna.

Theoretically, the reaction between water and rock could release approximately 0.5% of the hydrogen. Achieving a 1% efficiency threshold is crucial for practicality, and exploring deeper areas with higher temperatures may facilitate this, albeit at increased costs. However, these higher temperatures could also benefit geothermal energy generation.

There are vast amounts of iron-rich rock globally, and even at a 1% efficiency, the potential hydrogen yield could far surpass the current global production of 100 million tons.

Barbara Sherwood Lollar from the University of Toronto remarks on the growing interest in these innovative methods. “A collaborative approach that combines stimulated geological hydrogen production with CO2 mineralization shows great promise,” notes Aliaksey Patnia from the University of Oxford. “Numerous startups and research groups are exploring variations of this concept.”

If projects can successfully trap CO2, like Carbfix does, additional revenue could decrease risks, enhancing attractiveness to investors, Patonia explains. However, the viability of these strategies remains to be determined.

Sherwood Lollar urges an exploration of stimulated hydrogen production beyond the limited known natural hydrogen sources. Her team’s findings indicate that a mine in Timmins, Ontario, emits around 140 tons of hydrogen annually, presenting opportunities for local exploitation.

“There isn’t a single solution,” she emphasizes. “All these promising approaches can and should play a role, and we must address them promptly.”