Request for Information (RFI): Stimulating Geochemical Reactions in the Subsurface for in-situ Generation of Hydrogen and Helium Production

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Request for Information (RFI): Stimulating Geochemical Reactions in the Subsurface for in-situ Generation of Hydrogen and Helium Production This is a Request for Information (RFI) only. This RFI is not accepting applications for financial assistance. The purpose of this RFI is solely to solicit input for ARPA-E consideration to inform the possible formulation of future programs. The purpose of this RFI is to solicit input for a potential future ARPA-E research program focused on enabling technical advances which could lead to subsurface chemical reactors and gas separations. ARPA-E is seeking information to test the hypothesis that the subsurface can be used as a reactive environment to produce hydrogen at $1/kg, per DOE’s Hydrogen Shot target , and helium with no carbon emissions. Subsurface reactions have and do occur every day without human intervention, ranging from the mundane like abiogenic methane formation to the exotic like nuclear fission. The subsurface has a number of features which could make it amenable to performing chemical synthesis including hot temperatures (200-400+°F), high pressures, and catalytically relevant metals contained in rocks. It is already known that geothermal heat is a significant source of renewable energy. There are several initiatives devoted to resource discovery and development through the DOE’s Geothermal Technology Office which aim to use this thermal energy to produce electricity or to provide hot water and space heating. However, it may be possible to use this thermal energy for chemical synthesis. Typical deep geothermal temperature ranges (175-400°F) overlap well with chemical and other high-temperature processes. In addition to warm thermal conditions, the subsurface is characterized by high pressures. The pressure gradient at depth is related to hydrostatic pressure change (10 kPa/m). Pressures relevant to typical industrial processes can be accessed at depths that are well within the normal range of subsurface activities today. For example, a typical Haber Bosch process is done at pressures of 400 atm: approximately the same pressure found at a depth of 2 km. Finally, rocks may contain metals which are catalytically relevant for several industrial chemical processes. Nickel-iron alloys are frequently found in rocks and both nickel and iron are common catalytic metals in industrial processes. In this RFI, ARPA-E seeks to test the hypothesis of whether the temperature, pressure, and metals in the subsurface could be exploited for chemicals synthesis. ARPA-E is specifically interested in information to understand the technical potential of stimulating hydrogen generation in hard rock and hydrocarbon-rich basins. Within the context of hard rock, hydrogen is naturally produced via radiolysis where radioactive decay interacts with water to produce hydrogen and oxygen or via serpentinization where mafic and ultramafic rocks containing iron react with water in an oxidation-reduction reaction; the iron is oxidized and the water reduced to produce hydrogen and oxygen. Estimates of annual natural hydrogen production rates in terrestrial seeps place these rates equivalent to anywhere from 0.1-33% of today’s global hydrogen production from fossil fuels . Exact production rates are unknown, thereby contributing to the large variation in estimates, but it is clear that hydrogen-forming reactions occur in old, Precambrian rock which constitutes approximately 70% of the global continental crustal surface area. ARPA-E seeks information regarding the technical potential to stimulate hydrogen-forming reactions in old Precambrian rock as a way to produce clean hydrogen, using the subsurface as a georeactor. Another avenue that ARPA-E is exploring for producing hydrogen in the subsurface is by cracking hydrocarbons. Today, hydrogen is predominantly produced from hydrocarbons at the surface, either from steam methane reforming (76% of hydrogen production) or coal gasification (23%) . However, these processes are associated with significant carbon emissions, ranging from 9 tons CO2 per ton H2 in steam methane reforming to 19 tons CO2 per ton H2 in coal gasification. Minimizing the carbon footprint from hydrogen production in these instances will require retrofitting current processes to capture and sequester significant amounts of carbon, increasing the cost of hydrogen production overall and adding complexity to the process. ARPA-E is seeking insight to test the hypothesis that it can be more economical to produce hydrogen from fossil fuels in the subsurface, keeping the carbon in place and extracting only hydrogen at the surface. Producing hydrogen this way mitigates adding a separate carbon capture and sequestering step, but it is not clear if this is technically feasible or if it has the potential to be more economical than hydrogen production from fossil fuels with carbon capture and storage at the surface. To read the RFI in its entirety, please visit https://arpa-e-foa.energy.gov.

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