Mineral weathering is a geochemical process in which common rocks react with CO2 to form dissolved mineral bicarbonates. These bicarbonates wash into the ocean and over many thousands of years eventually precipitate as solid carbonate minerals. This process is the primary way that excess atmospheric CO2 is consumed and stored on geologic time scales, and explains why bicarbonate in seawater is the largest carbon reservoir on Earth's surface, holding the equivalent of 139,000 billion metric tonnes of CO2. For comparison, the atmosphere contains only about 3,100 billion metric tonnes of CO2. Each year some 1 billion metric tonnes of CO2, about 1/40 of human CO2 emissions, is consumed by this geochemistry.

Electro-geo-chemistry uses an electrochemical process to increase the rate of geochemical CO2 removal. This approach also produces energy in the form of hydrogen gas (H2). It uses saline water electrolysis in the presence of minerals to generate H2 while at the same time creating a highly reactive solution that acts like a chemical sponge, absorbing and converting CO2 into dissolved mineral bicarbonate. Adding this bicarbonate to the ocean not only provides long term carbon storage, but it also helps counteract ocean acidification. Thus, when powered by renewable electricity, this electro-geo-chemistry can be used to produce a non-fossil transportation fuel, H2, while simultaneously removing CO2 from the atmosphere and countering ocean acidification. The global abundances of the required materials and energy for this negative-emissions H2 process suggest that it can be done at very large scales.

How much CO2 it could absorb if everything worked perfectly?

A recent estimate ranges from about 90 to 900 billion tonnes (metric tons) per year as limited by the range of global renewable energy availability.
90-900Gt CO2
per year

Achieving even a fraction of such quantities would require the deployment of 10's of thousands of negative-emissions H2 plants. These would operate on the shoreline, in coastal waters, and/or in the open ocean on either stationary or mobile platforms at locations where seawater, renewable energy and minerals can be easily supplied, and where markets for the goods and services produced are close at hand.

In-depth description & science

The primary way that Nature consumes excess CO2 over geologic time scales is via rock/mineral weathering (Archer et al. 2009). Here, elevated CO2 acidifies the hydrosphere making carbonic acid that in turn reacts with the very large alkaline mineral reservoir on the Earth's crust to consume the acidity and CO2, forming dissolved mineral bicarbonates. These bicarbonates are then transported downstream to the ocean, explaining why, after a few billions years of mineral weathering, ocean bicarbonate is the largest carbon reservoir on the Earth's surface (38,000 Gt C primarily as dissolved bicarbonate or the equivalent of 139,000 Gt CO2). Ultimately, this C eventually precipitates from the ocean as carbonate minerals, thus entering even larger subsurface geologic storage. Given this very large global capacity to consume and store CO2, it is of interest to find ways of cost-effectively accelerating this process so that it is relevant on human/biologic rather than geologic time scales.

Over the past 10 years various methods of electrochemically accelerating the preceding mineral weathering have been discovered. All of these methods utilize the chemistry generated during water electrolysis to facilitate mineral decomposition and CO2 transformation to mineral bicarbonate, hence the term "electro-geo-chemistry". While this does require energy to effect air CO2 removal, at least half of the energy used can be recovered from the H2 produced in the process.

A recent analysis shows that the global potential for negative-emissions H2 to consume CO2 ranges from about 90 to 900 Gt CO2 /yr, based on the minimum and mean ranges in global renewable energy production potentials. For reference, annual human-caused CO2 emissions total about 40 Gt CO2/yr. Furthermore, negative-emissions H2 could also generate about 80,000 to 800,000 terrawatt hours per year (TWh/yr) of energy as H2. Current global energy use is about 160,000 TWh/yr meaning that negative-emissions H2 could in theory also satisfy global energy demand with zero emissions. The preceding capacities are significantly larger than the currently favored negative-emissions energy technology – Biomass Energy with Carbon Capture and Storage (BECCS). Yet negative-emissions H2 importantly avoids much of the land, water and nutrient impacts that would result from the enhanced land plant production required by BECCS.

But wait, there's more - Adding additional dissolved mineral bicarbonate to the ocean provides stable C storage and avoids the risk of having to transport and inject concentrated CO2 underground as required by CCS, BECCS and DAC. Also, amending seawater with additional mineral bicarbonate adds alkalinity, helping counter the effects of increasing CO2-derived ocean acidity and thus restoring ocean chemistry and biology (Marburini and Thake 1999, Albright et al. 2016), a process that naturally occurs via ambient global mineral weathering.

One variant of the preceding technology is to couple the negative-emissions H2 process with energy generated from direct microbial electrolysis as powered by the chemical energy contained in wastewater. This beneficially reduces waste organic matter in such effluent and converts the energy it contains to H2, while also removing the excess CO2 contained in the effluent and in air. The system is then net-positive in terms of energy generation and net negative with regard to CO2 emissions. In the process of feeding, housing and clothing 7.5 billion people on the planet, there is no shortage of wastewater with which to power such a negative-emissions energy system.

A second negative-emissions H2 variant is powered by Ocean Thermal Energy Conversion. OTEC has been researched for the past 100 years and utilizes the very large vertical thermal gradient in the ocean to generate electricity. One beneficial feature of OTEC is that it can be designed to cool the surface ocean. Since the surface ocean has received and stored more than 90% of the excess heat generated by human activity (IPCC 2013) and because this heat is impacting marine ecosystems, most notably the Great Barrier Reef, OTEC offers a way to help remove that heat to the deep ocean and hence help restore surface water ecosystems and provide global cooling. Conventionally, OTEC pumps seawater from a depth of 1000m to condense a working gas that vaporizes at the temperature of surface seawater. Placing a turbine electricity generator in the gas stream between the vaporizer and the condenser produces electricity. Releasing the cooling water at or near the ocean surface then cools the ocean downstream of the system. It also releases at the surface nutrients contained in the deep water, which could beneficially stimulate marine photosynthesis (natural or in aquaculture settings), effecting additional CO2 removal. We have also shown that such artificial upwelling of deep water by OTEC can be avoided (and OTEC efficiency increased) by allowing the working fluid (rather than seawater) to vertically transfer heat to the deep ocean.

What makes it a frontier technology?

Challenges - what is the non-starter:

The process is renewable-energy intensive.

However, other challenges exist as well. Without market incentives such as a carbon tax or credit, the cost of H2 production here will likely be uncompetitive with conventional sources of H2, e.g., H2 production via CO2-emissions intensive methane reforming. However, to get a better handle on negative-emissions H2 costs, benefits and impacts, significant investment in R&D is needed to better determine:

  1. optimum designs, energy sources, mineral sources, operating procedures and hence costs of this technology per tonne of H2 produced and CO2 consumed and stored.
  2. the environmental and social benefits and impacts of the technology. At large scales the integration/substitution of H2 into existing electricity and hydrocarbon fuel infrastructure would be required and likely disruptive.

What research needs to be done and which type of researchers would be required

Research is required to determine optimum electrolytes, electrodes, minerals types and sizes, cell configurations, and operating protocols. Both the upstream and downstream environmental impacts need to be determined and weighed against quantified environmental and climate benefits. Design, construction and testing at scale is required to determine economics, markets, siting, and social and geopolitical implications. The preceding would be done by individuals or companies with expertise in electrolytic H2 production, engineering and environmental assessment as well as those with economic, social, marketing and political expertise.

What infrastructure companies would be required for implementation

H2 manufacturers and distributors, renewable energy generators, together with engineering, environmental, economic, social and political consultants.

Energy requirements

It is estimated that 556 kWh of electricity is required by the negative-emissions H2 process to remove and store 1 t CO2. A 500 MW renewable energy power plant dedicated to negative-emissions H2 could therefore consume and store nearly 8 million tonnes of CO2 per day while generating a little more than 2 million kWh in the form of H2.

Energy Required

It is estimated that 556 kWh of electricity is required by the negative-emissions H2 process to remove and store 1 t CO2. Therefore, a 500,000 kW renewable energy power plant (generating 12 million kWh/day) dedicated to negative-emissions H2 could therefore consume and store nearly 21,600 tonnes of CO2 per day while generating about 6 million kWh of stored energy in the form of H2. The net energy consumption would then be 6 million kWh/day or in net, 278 kWh/tonne CO2 consumed. On the other hand, if one assumes that the energy produced must be in the form of electricity (not as stored H2) and assuming that the H2->electricity conversion efficiency (of H2 fuel cells) is 50%, then the net electricity consumption is 9 million kWh/day or 417 kWh/tonne CO2 removed. If the removal of 10 Gt CO2/yr (1/4 of annual anthropogenic CO2 emissions) is globally required, 5,560 TWh/yr of electricity or about 3.5% of current global energy use would be needed, while about 2,780 TWh/yr of stored energy would be created in the form of H2.

Connection to Other Ideas

  1. The technology could be powered by excess renewable energy to allow energy storage in the form of H2 that could then be converted back to electricity (via fuel cells) for use during periods of peak energy demand. Such energy storage is critically important for those forms of renewable energy that are intermittent, e.g., wind, solar, tidal, etc.
  2. Because gasoline refining uses large quantities of H2, use of negative-emissions H2 here could significantly reduce the net CO2 emissions footprint of conventional gasoline.
  3. The process could be coupled to and powered by waste water treatment, which would improve such treatment while generating energy and consuming CO2.
  4. If powered by OTEC, negative-emissions H2 would provide a negative-emissions method (H2) of transporting abundant offshore renewable energy onshore while also helping reduce surface ocean warming and ocean acidification. The downstream solution released by negative-emissions H2 will be rich in dissolved inorganic carbon and nutrients that could feed biological or chemical synthesis of valuable products.

Possible Business Models

Create a profitable business where the cost of conducting negative-emissions H2 is more than offset by the market value or $ credit of one or more of the following products/services:

  1. H2 as a negative-emissions fuel, energy storage medium or chemical feedstock
  2. CO2 removal and storage
  3. ocean antacid
  4. co-produced oxygen or chlorine gases
  5. co-produced silica
  6. C- and nutrient-rich solutions for subsequent biological or chemical synthesis

Initial analysis suggest that these revenue streams can significantly offset the cost of production, thus making a energy source, H2, that has very low or negative net cost, potentially the lowest of any energy source.

Estimated Costs

The estimated cost of energy production by negative-emissions H2 systems ranges from $0.07 to $0.63/kWh H2 while the predicted cost of CO2 removal ranges from $3 to $161/t CO2, such variations being a direct function of the cost of input renewable electricity, $0.01 to $0.29/kWh (Rau et al. 2018) and the market value of the H2 produced. These CO2 removal costs are equivalent to or substantially lower than those reported for DAC, CCS and BECCS. Therefore, if the global removal of 10 Gt CO2/yr is required, the estimated cost would be $30-1,610B/yr depending on the unit cost of renewable electricity ranging from $0.01 to $0.29/kWh and an H2 market value of $0.06/kWh(as stored H2).


Negative-emissions H2 has only been demonstrated at small scales although related, larger prototypes of electrochemical seawater C and H2 stripping have been tested. While conventional water electrolysis has an energy conversion efficiency of about 70%, it is not known if similar efficiencies can be attained by negative-emissions H2, given the additional complexity of adding minerals to the anolyte and removing the alkalinity generated. While seawater would be the perfect electrolyte from a cost and capacity standpoint, seawater electrolysis discharges chlorine gas, Cl2, rather than oxygen gas, O2, at the anode. However, this might be avoided by the use of demonstrated O2-selective anodes.

Also unknown are the downstream marine environmental impacts of alkalinity addition, if any. The ocean receives about 1 Gt CO2 in the form of dissolved mineral bicarbonate from natural mineral weathering with no ill effects to the ocean being apparent. The few, small-scale experiments done to investigate the effects of artificially elevated alkalinity have shown positive responses to resident biota. However, further research is needed to confirm that such addition at large scales would be benign if not beneficial and restorative. Upstream environmental impacts would stem from the increased mineral extraction, processing and transport needed to conduct negative-emissions H2 at large scales. A better understand of environmental and monetary costs/benefits is required before this technology can be widely deployed.

Assuming that seawater can be used as the water and electrolyte source and that the ocean will be the recipient of the bicarbonate produced, the negative-emissions H2 will be geographically limited to coastal, near-shore or open ocean settings (about 70% of the Earth's surface).

What is the 2040 vision for the idea?

Negative-emissions H2 is proven to have high global energy production and CO2 removal capacities while also providing additional environmental benefits, all at a cost that is very competitive with if not lower than other approaches. An entirely new global energy economy based on H2 arises that can safely and economically harness the vast coastal and open ocean renewable energy, drastically reducing global fossil energy use and CO2 emissions and the geopolitical and climate tensions thereof. The generation of this negative-emissions energy is accomplished without significantly impacting global food, fiber and fuel production as would BECCS at equivalent scales. A grateful world rejoices, Nobel Prizes awarded, etc.

2018 2040


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