Marine CDR (mCDR) Green H₂ Co-Product Alkalinity Enhancement

Direct Ocean Carbon Capture & mCDR Lab

Model marine dissolved inorganic carbon (DIC) extraction, bipolar membrane electrodialysis (BPMED), ocean alkalinity enhancement (OAE), green hydrogen co-products, and 20-year net LCOR ($/t CO₂).

Calibrated Marine Facility Presets:
Net LCOR (with H₂)
$0.0/t
After green H₂ credit
Gross LCOR
$0.0/t
Gross Capex + Opex
20-Yr Project NPV
$0.0M
Unlevered DCF
Unlevered IRR
0.0%
Internal rate of return
Capital Payback
0.0 yrs
Cumulative cash break-even
Total Initial Capex
$0.0M
Plant + MRV sensors
mCDR Facility & Chemical Inputs
1. Scale & Ocean Chemistry
MT CO₂/yr
2. Specific Energy & Power
kWh/ton
$/kWh
3. CDR Credits & Hydrogen Value
$/ton net
$/kg H₂
4. Capital Cost & Hurdle Rate
$/t/yr
Annual Production & Operating Pro-Forma Summary
Ocean Water & H₂
Seawater Intake: 0 m³/day
Green H₂ (kg/yr): 0 kg
Green H₂ (MT/yr): 0 MT
Specific Energy: 0 kWh/t
Annual Financials ($M)
CDR Credit Rev: $0.00M
Green H₂ Offtake: $0.00M
Gross Revenue: $0.00M
Annual EBITDA: $0.00M
Cost of Removal ($/t)
H₂ Co-Product Credit: -$0.0/t
Electricity Cost: $0.0/t
Capital Recovery: $0.0/t
O&M + MRV: $0.0/t
5×5 Sensitivity Matrix: Electricity Tariff ($/kWh) vs CDR Credit Price ($/t CO₂)

Displays 20-Year Project NPV ($M) and Net Levelized Cost of Removal (LCOR $/t CO₂) across varying clean electricity tariffs and voluntary carbon market credit prices.

Technical Reference: Ocean Carbon Chemistry, Electrodialysis & MRV
1. Marine Carbonate System & DIC Equilibrium

The global oceans store roughly 38,000 gigatons of carbon, making seawater the largest active reservoir of carbon on the planet. Dissolved Inorganic Carbon (DIC) exists in dynamic chemical equilibrium across three species:

CO2 (aq) + H2O ⇔ H2CO3 ⇔ H+ + HCO3- (≈ 90%) ⇔ 2 H+ + CO3(2-) (≈ 9%)

At typical seawater pH (\(7.8\text{--}8.2\)), over \(90\%\) of inorganic carbon is stored as bicarbonate (\(\text{HCO}_3^-\)). Because seawater holds \(\sim 2.1\text{ mmol DIC/kg}\) (equivalent to \(90\text{--}100\text{ g CO}_2/\text{m}^3\)), it is roughly \(120\text{ to }150\text{ times more carbon-dense than ambient air}\). Direct Ocean Capture avoids the colossal volumetric air-handling infrastructure required by Direct Air Capture (DAC).

2. Bipolar Membrane Electrodialysis (BPMED) & Seawater Splitting

BPMED stacks contain alternating cation, anion, and bipolar ion-exchange membranes. Applying a direct electrical current causes water dissociation at the bipolar catalyst layer:

H2O → H+ (acid channel) + OH- (base channel)

Acidifying an ocean slip-stream to \(\text{pH }4.0\text{--}4.5\) shifts the carbonate equilibrium completely toward gaseous \(\text{CO}_2\), which is degassed in packed vacuum contactor towers. Concurrently, electrochemical reduction at the cathode generates green hydrogen:

2 H2O + 2 e- → H2 ↑ + 2 OH- (∼ 38.5 kg H2 per metric ton CO2 stripped)

The alkaline stream is recombined with the degassed seawater, restoring or elevating the pH to prevent localized acidification before discharge.

3. Ocean Alkalinity Enhancement (OAE) & Permanent Mineral Storage

Ocean Alkalinity Enhancement (OAE) dissolves basic minerals—such as olivine \(((\text{Mg, Fe})_2\text{SiO}_4)\), slaked lime \((\text{Ca(OH)}_2)\), or brucite \((\text{Mg(OH)}_2)\)—into coastal surface waters. This consumes dissolved aqueous carbonic acid and forms stable bicarbonate:

CO2 (aq) + H2O + OH- → HCO3- (Dissolved Marine Bicarbonate)

Bicarbonate ions have an oceanic residence time exceeding \(10,000\text{ to }100,000\text{ years}\). Furthermore, increasing ocean total alkalinity (TA) directly counteracts anthropogenic ocean acidification, restoring carbonate saturation states (\(\Omega_{\text{arag}}\)) essential for coral reefs and calcareous plankton.

4. Measurement, Reporting & Verification (MRV) Protocols

High-integrity carbon credit issuance requires robust MRV. Marine CDR projects deploy continuous sensor buoys measuring partial pressure of carbon dioxide (\(p\text{CO}_2\)), pH, Total Alkalinity (TA), and Dissolved Inorganic Carbon (DIC) across upstream intakes and downstream plume dispersion zones. Coupled hydrodynamic biogeochemical models (e.g. ROMS or FVCOM) verify air-sea gas exchange equilibration and quantify atmospheric drawdown over 6 to 18-month cycles.

Formative Assessment: Ocean Chemistry & Marine CDR Quiz
Frequently Asked Questions (FAQ)

Direct Ocean Capture (DOC) and Marine Carbon Dioxide Removal (mCDR) encompass technological and chemical processes that remove dissolved inorganic carbon (DIC) directly from ocean waters or enhance ocean alkalinity to draw down atmospheric CO2. The Earth's oceans hold approximately 38,000 gigatons of carbon—over 45 times more than the atmosphere. By capturing CO2 from seawater or enhancing its chemical buffering capacity, mCDR leverages the ocean's natural equilibrium with the atmosphere to achieve permanent, gigaton-scale carbon dioxide removal without competing for arable land or freshwater.

Bipolar membrane electrodialysis (BPMED) applies an electric current across specialized ion-exchange membranes to dissociate water into protons (H+) and hydroxide ions (OH-) without adding hazardous chemicals. By mixing the generated acid stream with a portion of incoming seawater, the pH is lowered to approximately 4.0 to 4.5. This shifts the carbonate equilibrium (HCO3- + H+ -> CO2 + H2O), releasing dissolved bicarbonate as concentrated gaseous CO2 that is easily extracted using a vacuum contactor or membrane degasser. The alkaline stream (OH-) is subsequently used to neutralize the effluent back to normal marine pH (7.8 to 8.2) before ocean return.

Direct Air Capture (DAC) must process ambient air where CO2 is extremely dilute (~420 ppm, or ~0.77 g CO2 per m3), requiring massive fans and enormous land footprints. In contrast, seawater holds approximately 90 to 100 grams of CO2 equivalent per m3—over 120 times more concentrated than air. As a result, Direct Ocean Capture moves over two orders of magnitude less fluid volume per ton of CO2 captured, avoiding giant air contactor capital costs and benefiting from seawater's high electrical conductivity.

Ocean Alkalinity Enhancement (OAE) accelerates the natural silicate and carbonate weathering cycle by adding alkaline minerals (such as ground olivine, calcium silicate, or electrochemical hydroxides) into surface waters. The added alkalinity reacts with excess aqueous carbonic acid (H2CO3) to form stable, non-volatile bicarbonate (HCO3-) and carbonate (CO3(2-)) ions. This permanently locks carbon away for 10,000 to 100,000 years while de-acidifying marine ecosystems, protecting coral reefs and shellfish from ongoing anthropogenic ocean acidification.

In electrochemical seawater splitting systems, water reduction at the cathode produces approximately 35 to 40 kg of pure green hydrogen (H2) for every metric ton of CO2 removed. Selling this clean hydrogen to industrial or mobility off-takers at $3.00 to $5.00/kg generates $110 to $190 in co-product revenue per ton of CO2. This revenue stream directly offsets electric power tariffs and membrane capital recovery, lowering the net levelized cost of carbon removal (LCOR) from a gross cost of $250-$350/t down to an effective net cost of $120-$180/t.
Explore Carbon Removal & Clean Transition Simulations
Direct Air Capture
DAC Carbon Removal Lab

Model solid sorbent vs liquid solvent direct air capture, thermal regeneration, and levelized net CDR costs.

Launch DAC Lab →
Point-Source CCS
CCUS & 45Q Storage Lab

Model amine capture, parasitic power, saline aquifer storage, and Section 45Q tax credits ($85/ton).

Launch CCUS Lab →
Biochar Sequestration
Biochar Carbon Removal Lab

Model biomass slow pyrolysis, carbon permanence, soil application, and voluntary CORC carbon credits.

Launch Biochar Lab →
Clean Hydrogen
Green Hydrogen LCOH Lab

Model PEM vs alkaline water electrolysis, stack degradation, power tariffs, and levelized hydrogen costs.

Launch LCOH Lab →