Marine Carbon Capture
Executive Summary
We found four viable paths to 5-year marine survival. The simplest borrows directly from desalination—polarity reversal every 15-30 minutes dissolves scale and kills biofilms before they mature. If you want a commercially proven approach, Equatic has validated chlorine-accepting architecture at pilot scale. The higher-risk alternative is designing for replacement rather than survival: modular hot-swap electrodes that make 1-year component life acceptable.
Do you want to use a commercially proven approach (chlorine-accepting) or pursue potentially lower-cost alternatives (polarity reversal, Mg anode)? The first gives you speed, the others give you potential cost advantage.
Solvable
Multiple paths exist, including one that's commercially proven. The technical problem is more solved than you might expect.
Start with Equatic outreach to understand their licensing/partnership options—if acceptable, you have a fast path. In parallel, run a 3-month polarity reversal validation ($50-100K) to test the lower-cost alternative. This gives you answers on both paths quickly.
The Brief
Electrochemical ocean alkalinity enhancement produces NaOH at sea to absorb atmospheric CO2. But marine electrolysis faces severe corrosion, biofouling, and membrane fouling. Need electrolyzer architecture that survives 5+ years in marine environment at <$80/ton CO2 equivalent alkalinity cost.
Problem Analysis
Seawater destroys electrochemical systems through three simultaneous attack vectors: chloride ions corrode metals and degrade membranes within weeks; biofilms establish within 24-48 hours and mature into impermeable layers within weeks; and at cathode pH >10, Mg(OH)₂ and CaCO₃ precipitate directly onto electrode surfaces, creating insulating scale that kills efficiency. Current approaches designed for purified brine fail catastrophically—chlor-alkali membranes tolerate <50 ppb divalent cations while seawater contains 400 ppm Ca²⁺ and 1300 ppm Mg²⁺, a 10,000x mismatch.
The fundamental challenge is thermodynamic: chlorine evolution (1.36V) is kinetically favored over oxygen evolution (1.23V) on most catalysts in chloride-rich solutions, despite oxygen being thermodynamically preferred. The 490mV window exists but requires precisely engineered catalyst surfaces to exploit. Simultaneously, the cathode operates at pH >10 where both Mg(OH)₂ (Ksp = 1.8×10⁻¹¹) and CaCO₃ (Ksp = 3.4×10⁻⁹) are supersaturated by orders of magnitude—precipitation is thermodynamically inevitable. And biofilm formation follows predictable kinetics: conditioning film (proteins, organics) in minutes, bacterial attachment in hours, mature community in days. You cannot thermodynamically prevent any of these; you can only manage them kinetically.
E_cell = E°_OER - E°_cathode + η_OER + η_cathode + iR_solution + iR_membrane + iR_fouling
Cell voltage includes thermodynamic minimum (1.23V for OER) plus overpotentials at each electrode plus ohmic losses. The fouling resistance term (iR_fouling) grows exponentially with time in seawater, eventually dominating. At 100 μm biofilm thickness, mass transport resistance increases 10-100x.
Optimize for $/kg-NaOH-lifetime, not component longevity
The 5-year electrode life target may be self-imposed rather than economically optimal. If electrode replacement is cheap and fast enough (modular cartridges, quick-connect interfaces), designing for 6-12 month disposable electrodes might beat 5-year hardened electrodes on total cost. The offshore wind industry accepts regular blade inspections and component replacement; the question is whether the electrolyzer industry's longevity obsession reflects optimal economics or inherited assumptions from chlor-alkali plants that operate with purified brine.
Adapted chlor-alkali cells with Nafion membranes and DSA anodes
Designed for purified brine; membranes foul in days-weeks with seawater; DSA anodes preferentially produce chlorine over oxygen
Bipolar membrane electrodialysis (BPMED)
30-40% lower energy than direct electrolysis but membrane life in seawater is weeks without aggressive pretreatment
Heavy pretreatment to chlor-alkali standards
Adds $20-40/ton NaOH equivalent; defeats the purpose of using seawater directly
Selective OER catalysts (NiFe LDH)
Lab-proven >99% selectivity but long-term stability in real seawater (with organics, suspended solids) unvalidated
Equatic (UCLA spin-out)[1]
Flow-through mesh electrodes accepting chlorine co-production, downstream mineral neutralization
$100-150/ton CO2 at pilot scale (disclosed in DOE ARPA-E documentation)
$50-70/ton CO2 at commercial scale by 2027
Ebb Carbon[2]
Electrochemical ocean alkalinity enhancement with proprietary electrode design
Not disclosed; pilot operations in 2023
Commercial deployment by 2026
Planetary Technologies[3]
Electrochemical production of Mg(OH)₂ from industrial waste streams
Pilot scale; cost not disclosed
1 Mt CO2/year capacity by 2030
Kuang et al. (Stanford)[4]
NiFe LDH catalyst achieving >99% OER selectivity in seawater
100+ hours stability at 400 mA/cm² demonstrated
Academic research; no commercialization timeline
[1] DOE ARPA-E award documentation and company disclosures, 2022-2023
[2] Press releases, unverified
[3] Company announcements
[4] PNAS 2019
[1] DOE ARPA-E award documentation and company disclosures, 2022-2023
[2] Press releases, unverified
[3] Company announcements
[4] PNAS 2019
Constraints
- Must operate in seawater (~19,000 ppm Cl⁻, ~400 ppm Ca²⁺, ~1300 ppm Mg²⁺)
- Must produce net alkalinity (NaOH, Mg(OH)₂, or equivalent)
- Cannot release significant chlorine to environment (<5% of current as Cl₂)
- Must be deployable offshore or coastal
- 5+ year system life (component replacement acceptable)
- <$80/ton CO2 equivalent (may be negotiable with carbon credit pricing)
- Continuous operation preferred but intermittent acceptable
- Minimal pretreatment preferred but some acceptable if cost-effective
- Temperate coastal waters (~15°C average); tropical deployment would accelerate biofouling 2-3x
- Grid-connected or offshore wind power at $30-60/MWh
- Direct operational cost only; MRV costs excluded (would add $10-30/ton)
- Electrochemical approach required; mineral dissolution alternatives noted but not primary focus
Alkalinity production cost
Unit: $/ton CO2
Mean time between maintenance
Unit: months
Capacity factor
Unit: percent
Energy consumption
Unit: kWh/kg
Chlorine selectivity (OER vs CER)
Unit: percent Faradaic efficiency
First Principles Innovation
Instead of asking 'how do we make components survive 5 years in seawater,' we asked 'how do we make component replacement so cheap and fast that survival doesn't matter.'
Solutions
We identified 7 solutions across three readiness levels.
Start with the Engineering Path. Run R&D in parallel if you need breakthrough potential or competitive differentiation.
Engineering Path
Proven technologies, often borrowed from other industries. The work is adaptation, integration, and validation, not discovery.
Polarity Reversal + Modular Cartridge Architecture
Combine proven EDR-style polarity reversal (5-15 minute cycles for seawater) with modular cartridge electrodes designed for 6-12 month hot-swap replacement. The system accepts that seawater will degrade components and optimizes for total cost of ownership rather than component longevity.
Polarity reversal works by periodically switching anode and cathode. When current reverses, the former cathode (where Mg(OH)₂ and CaCO₃ precipitated at high pH) becomes the anode (low pH), dissolving the scale. Biofilms lose the ion gradient cues they need for attachment and detach. The Mikhaylin & Bazinet 2016 review documents 5-10x membrane life extension with this single intervention in brackish water; seawater may require more frequent reversal (5-15 minutes vs. 15-30 minutes) due to higher divalent cation load. Modular cartridges use standardized quick-connect interfaces allowing tool-free electrode stack replacement without cell disassembly. This follows the black liquor electrolysis philosophy of 'managed degradation'—accept that electrodes will wear, design for easy replacement, and optimize $/kg-NaOH-lifetime rather than $/year-operation. Cartridge materials can be simpler (carbon, nickel) rather than exotic alloys because they don't need to survive 5 years.
CaCO₃ solubility increases ~100x from pH 10 to pH 4; Mg(OH)₂ dissolves completely below pH 9.5. When polarity reverses, the former cathode experiences acidic conditions that dissolve accumulated scale. Biofilm EPS matrix loses structural integrity when local ionic strength and pH oscillate—the Mikhaylin & Bazinet review documents 50-80% biofilm detachment per reversal cycle. The key is reversing frequently enough that scale and biofilm never reach the 'mature' stage where they become mechanically robust and difficult to remove.
Periodic electrochemical stress disrupts fouling equilibrium before irreversible attachment occurs
Desalination industry (electrodialysis reversal). EDR systems reverse polarity every 15-30 minutes to prevent membrane fouling in brackish water treatment
The physics is identical—scale dissolution at low pH, biofilm disruption from ionic oscillation. Seawater just requires more frequent reversal.
The electrolyzer industry inherited chlor-alkali assumptions about continuous operation with purified feed. EDR is standard in desalination but the communities don't overlap. The 5-year electrode life target may be self-imposed rather than economically optimal.
Solution Viability
Core physics is proven in EDR desalination (Mikhaylin & Bazinet 2016 documents 5-10x membrane life extension). The adaptation to seawater alkalinity production requires validation of reversal frequency and energy penalty in real seawater conditions.
What Needs to Be Solved
Optimal polarity reversal frequency for seawater with 10,000x higher divalent cation load than brackish water
If reversal needs to be too frequent (e.g., every 2-3 minutes), energy penalty may exceed 20%, making this approach uneconomical vs. chlorine-accepting alternatives.
EDR literature shows 15-30 minute cycles for brackish water. Seawater has ~10,000x more Ca²⁺/Mg²⁺, so more frequent reversal is expected, but exact requirement unknown.
Path Forward
3-month seawater exposure test with reversal frequency optimization. Vary cycles from 5-15 minutes, measure electrode degradation, fouling, and energy consumption.
Physics is well-understood. Mikhaylin & Bazinet review shows consistent results across different systems. Main uncertainty is optimization, not fundamental viability.
You (internal team)
Weeks
$50-100K
If You Pursue This Route
Contact Xylem/Evoqua (856-507-9000) or Veolia Water Technologies for EDR system quotes and technical consultation on seawater adaptation.
If 3-month test shows <30% electrode degradation and <15% energy penalty, proceed to pilot. Otherwise, evaluate chlorine-accepting fallback.
Run a New Analysis with this prompt:
“Detailed reversal protocol optimization study: "Design an EDR-based alkalinity production system optimized for direct seawater feed"”
If This Doesn't Work
Accept Chlorine + Downstream Mineral Neutralization
Energy penalty >20% or electrode degradation >50% in 3-month test indicates reversal frequency required is too high for economic operation.
2.8-3.2 kWh/kg NaOH (5-15% energy penalty from reversal)
6-12 months to pilot validation
$0.5-2M for pilot system
- Polarity reversal frequency required for seawater may be so high that energy penalty exceeds 20%
- May not work in tropical/humid environments where drying is slow
- Capacity factor loss (5-15%) may exceed fouling-related gains
3-month seawater exposure test with polarity reversal protocol optimization
Method: Deploy test electrodes in real seawater; vary reversal frequency; measure electrode weight loss, surface morphology, electrochemical performance, fouling coverage
Success: Electrode performance degradation <30% over 3 months; scale thickness <50 μm; biofilm coverage <20% of surface area
If degradation >50% or scale >100 μm, increase reversal frequency or pivot to chlorine-accepting architecture
Accept Chlorine + Downstream Mineral Neutralization
Stop fighting chlorine evolution at the anode. Accept mixed Cl₂/O₂ production and react chlorine with olivine or limestone slurry downstream.
This is the Equatic approach, commercially validated at pilot scale. At the anode, seawater electrolysis produces both O₂ and Cl₂ (ratio depends on catalyst and conditions). Cl₂ hydrolysis produces HOCl/HCl. This acidic stream contacts olivine (Mg₂SiO₄): 2HCl + Mg₂SiO₄ → MgCl₂ + H₄SiO₄. The net reaction consumes acid and produces dissolved cations that represent alkalinity when discharged to the ocean.
HOCl (pKa 7.5) and HCl from chlorine hydrolysis attack mineral surfaces. Olivine dissolution: Mg₂SiO₄ + 4H⁺ → 2Mg²⁺ + H₄SiO₄. Each mole of Cl₂ produces 2 moles of H⁺, which can dissolve ~1 mole of Mg from olivine. The Mg²⁺ released represents 2 equivalents of alkalinity. Net effect: chlorine becomes a positive contributor to alkalinity production.
Solution Viability
This is the Equatic approach, commercially validated at pilot scale. DOE ARPA-E documentation shows $100-150/ton CO2 at pilot with roadmap to $50-70 by 2027. The physics is proven—it's an operational and scale-up challenge, not a technical one.
What Needs to Be Solved
Olivine sourcing at scale and regulatory pathway for ocean discharge
Olivine availability and permitting could constrain deployment location and speed, but these are business challenges, not technical blockers.
Equatic and Planetary Technologies have both secured mineral supplies and initial permits. The pathway exists.
Path Forward
Secure olivine supply contract and engage with EPA/NOAA on ocean discharge permits for your target deployment site.
Equatic and Planetary have both navigated this. EPA Science Advisory Board has reviewed OAE favorably. Regulatory risk is real but manageable.
Industry Partner
Months
$200-500K for permitting process
If You Pursue This Route
Contact Equatic (UCLA spin-out) about licensing or partnership. They've solved the mineral integration at pilot scale.
If polarity reversal energy penalty proves >20%, this becomes the primary path forward.
Run a New Analysis with this prompt:
“Detailed analysis: "Compare chlorine-accepting vs. selective OER architectures for marine alkalinity enhancement"”
If This Doesn't Work
Sacrificial Magnesium Anode Architecture
If mineral sourcing or permitting proves intractable at your target scale/location, the Mg anode approach eliminates both issues.
If selective OER catalysts prove unreliable in real seawater, or if polarity reversal energy penalty is unacceptable, the chlorine-accepting architecture becomes primary. Also preferred if mineral co-benefits (silica for agriculture, Mg for ocean chemistry) have value.
Geothermal-Inspired Precipitation Steering
Install sacrificial 'scaling targets' upstream of electrodes that preferentially nucleate Mg(OH)₂ and CaCO₃.
Replace scaling targets on maintenance cycles while electrodes remain clean. This is standard practice in geothermal power plants like Wairakei (NZ), which has operated for 60+ years with severe silica and carbonate scaling. Heterogeneous nucleation of mineral scale preferentially occurs on surfaces with high surface area, surface defects/roughness, and favorable surface chemistry. By placing intentionally rough, high-surface-area targets in the flow path before electrodes, supersaturated Ca²⁺ and Mg²⁺ preferentially nucleate on these sacrificial surfaces.
Nucleation theory: critical nucleus formation requires overcoming an energy barrier that depends on surface energy. Rough surfaces with high defect density provide low-energy nucleation sites. If scaling targets provide 10-100x more favorable nucleation sites than smooth electrode surfaces, >90% of precipitation occurs on targets rather than electrodes.
Solution Viability
Standard practice in geothermal plants like Wairakei (NZ), operating for 60+ years with severe silica and carbonate scaling. Nucleation physics is well-understood and directly transferable. This is proven technology requiring only adaptation.
What Needs to Be Solved
No fundamental blocker—this is complementary to all primary approaches
The only risk is whether scaling targets are effective enough in high-flow marine conditions. Lab validation recommended but not gating.
Geothermal precedent is strong. Main uncertainty is adaptation to marine electrolyzer geometry and flow rates.
Path Forward
Include sacrificial scaling targets in the 3-month pilot test. Compare electrode fouling with and without targets.
Nucleation theory is robust. If rough, high-surface-area targets provide 10-100x more favorable nucleation sites than smooth electrodes, >90% of precipitation should occur on targets.
You (internal team)
Days
$5-10K for materials and installation
If You Pursue This Route
Add scaling targets to your pilot design. Use porous ceramic or roughened stainless steel plates upstream of electrodes.
If targets reduce electrode fouling by >50% in pilot, include in production design. Otherwise, rely on polarity reversal alone.
Run a New Analysis with this prompt:
“Detailed analysis: "Optimize precipitation steering geometry for marine electrolyzer systems"”
If This Doesn't Work
Polarity Reversal + Modular Cartridges
If scaling targets prove ineffective in marine conditions, polarity reversal alone should still achieve acceptable fouling management.
This is complementary to all other approaches—should be included in any system design regardless of primary architecture. Low cost, low risk, proven physics.
Intermittent Drying Cycle Operation
Optimize for intermittent operation with deliberate drying cycles rather than continuous submersion.
When electricity is unavailable (renewable intermittency) or during scheduled intervals, drain cells and allow surfaces to dry. Biofilms die without moisture (90-99% mortality after 4-8 hours drying); mineral scale becomes brittle and spalls from thermal expansion mismatch. This turns the weakness of intermittent renewables into a fouling management strategy. The intertidal zone demonstrates this naturally—organisms in the splash zone face much lower fouling pressure than continuously submerged surfaces.
Biofilm EPS is 90%+ water; desiccation causes irreversible collapse of the hydrogel structure. Gram-negative bacteria (dominant marine foulers) are particularly sensitive. CaCO₃ scale has thermal expansion coefficient ~6×10⁻⁶/°C vs ~12×10⁻⁶/°C for metals; temperature cycling during drying creates interfacial stress that propagates cracks.
Solution Viability
Biology is solid—biofilms are 90%+ water and die within 4-8 hours of desiccation. Scale becomes brittle from thermal expansion mismatch. The intertidal zone demonstrates this naturally. However, effectiveness in enclosed electrolyzer cells vs. open surfaces needs validation.
What Needs to Be Solved
Whether drying cycles are practical in enclosed electrolyzer cell geometries
If cells cannot be properly drained and dried without disassembly, this approach adds complexity without benefit.
The physics is proven for exposed surfaces. Enclosed cell geometries may trap moisture and prevent effective drying.
Path Forward
Design electrolyzer cells with drain ports and test drying effectiveness. Measure residual moisture after drain cycle and correlate with biofilm mortality.
Cell geometry modifications are straightforward. Main uncertainty is whether practical drying times (4-8 hours) align with renewable intermittency patterns.
You (internal team)
Weeks
$20-30K for cell modification and testing
If You Pursue This Route
Add drain capability to pilot cell design. Track biofilm coverage vs. drying cycle frequency and duration.
If drying cycles reduce biofilm coverage by >80% without excessive operational complexity, include in production design.
Run a New Analysis with this prompt:
“Detailed analysis: "Optimize electrolyzer architecture for intermittent operation with offshore wind power"”
If This Doesn't Work
Polarity Reversal + Modular Cartridges
If drying proves impractical, rely on polarity reversal for biofouling control. Drying may still be valuable in tropical deployments where biofouling is most severe.
Complementary to polarity reversal. Particularly valuable for offshore wind-powered systems where intermittency is inherent. May become primary fouling management in tropical deployments where biofouling is most severe.
R&D Path
Fundamentally different approaches that could provide competitive advantage if successful. Pursue as parallel bets alongside solution concepts.
Sacrificial Magnesium Anode Architecture
Flip the paradigm: instead of protecting electrodes from corrosion, design the anode to corrode productively. Magnesium sacrificial anodes dissolve to produce Mg(OH)₂ directly—the anode IS the alkalinity product. No membrane needed because there's no chlorine production. Pair with inert cathode for hydrogen evolution. Magnesium metal spontaneously oxidizes in seawater: Mg → Mg²⁺ + 2e⁻. At the cathode, water reduces: 2H₂O + 2e⁻ → H₂ + 2OH⁻. The Mg²⁺ and OH⁻ combine to form Mg(OH)₂ (brucite), which is sparingly soluble and disperses as alkaline suspension. This eliminates the membrane entirely—there's no chlorine to separate because there's no oxidation of water or chloride at the anode, only metal dissolution. It eliminates biofouling on the anode because the surface is constantly dissolving. It eliminates the chlorine selectivity problem because no chlorine can form.
Magnesium dissolution proceeds through direct electrochemical oxidation: Mg → Mg²⁺ + 2e⁻ (E° = -2.37V vs SHE). In seawater, the reaction is spontaneous and fast. The Mg²⁺ immediately hydrolyzes: Mg²⁺ + 2OH⁻ → Mg(OH)₂. Each mole of Mg produces 2 moles of OH⁻ equivalents = 3.4 g OH⁻/g Mg. No chlorine can form because there's no oxidation reaction at the anode—only metal dissolution. Energy requirement is theoretically zero (galvanic); <0.5 kWh/kg NaOH equivalent with enhancement current.
The electrode can BE the product—dissolution is production, not failure
If it works: Eliminates membrane, chlorine, and fouling problems simultaneously. Simplest possible architecture.
Improvement: Energy consumption could drop from 2.5-3.5 kWh/kg to <0.5 kWh/kg (galvanic + enhancement)
Solution Viability
The electrochemistry is sound—Mg sacrificial anodes have 70+ years of field data in cathodic protection (DNV-RP-B401 standard). The paradigm shift is treating dissolution as production, not failure. Key uncertainty is whether Mg(OH)₂ passivation can be managed at practical dissolution rates.
What Needs to Be Solved
Mg(OH)₂ passivation layer may slow dissolution below economically useful rates
If dissolution rate falls below ~5 mm/year, the system cannot produce alkalinity fast enough to justify infrastructure cost. The passivation layer that forms naturally is the key uncertainty.
Cathodic protection literature shows variable passivation behavior depending on alloy composition, flow rate, and current density. Controllable but needs optimization.
Path Forward
Bench test: Buy marine-grade Mg anodes from cathodic protection supplier (Galvotec 956-630-3500 or Farwest sales@farwestcorrosion.com). Deploy in seawater with inert cathode. Test dissolution rate under varying current densities and flow rates. Target >5 mm/year sustained dissolution.
Cathodic protection data suggests controllable dissolution is achievable. Main uncertainty is whether passivation management adds unacceptable complexity or cost.
You (internal team)
Weeks
$20-40K
If You Pursue This Route
Order AZ91 or AM60 Mg alloy anodes from Galvotec (956-630-3500) or Farwest (sales@farwestcorrosion.com). These alloys have controlled dissolution characteristics.
If sustained dissolution >5 mm/year is achievable with reasonable flow/current, proceed to pilot. If passivation kills dissolution, reject this approach.
Run a New Analysis with this prompt:
“Detailed analysis: "Design a sacrificial Mg anode system for marine alkalinity production"”
If This Doesn't Work
Accept Chlorine + Downstream Mineral Neutralization
If passivation cannot be managed cost-effectively, the chlorine-accepting architecture is the proven fallback. Equatic has demonstrated it works.
Electrochemical Olivine Weathering Cell
Electrochemically accelerate olivine dissolution instead of splitting water
Ceiling: Lower energy than direct electrolysis; complete elimination of chlorine problem; mineral acts as both feedstock and buffer
Key uncertainty: Silica gel formation from H₄SiO₄ polymerization could clog reactors; mineral passivation by secondary precipitates could limit conversion
Elevate when: If silica management proves straightforward and energy consumption is <2 kWh/kg, this becomes primary path due to lower energy than direct electrolysis and elimination of chlorine problem.
NASICON Solid-State Membrane Architecture
Replace polymer membranes with ceramic Na⁺ conductors impermeable to seawater
Ceiling: Eliminates biofouling, organic fouling, and chloride attack on cathode side entirely. Potential for very long membrane life.
Key uncertainty: Mechanical brittleness of ceramics makes large-area membranes challenging; sealing ceramic to housing in seawater environment is unproven
Elevate when: If polymer membrane costs or PFAS regulations become prohibitive, and if ceramic manufacturing scales, this becomes primary path for long-term durability.
Frontier Watch
Technologies worth monitoring.
Galinstan Liquid Metal Cathode
PARADIGM2
Self-renewing liquid surface that cannot be permanently fouled
Mercury cells operated reliably for 80+ years; abandonment was environmental, not technical. If Galinstan electrochemistry proves viable, this could be the ultimate fouling-resistant architecture.
Sodium solubility in Galinstan (~0.5-1 at.%) may limit practical rates. Gallium embrittlement of structural metals requires careful material selection. Gallium and indium supply chains are constrained (~300 and ~800 tons/year respectively). Fundamental electrochemistry research needed.
Trigger: Publication demonstrating >1 at.% Na solubility in Ga-based alloy, or Ambri-style liquid metal battery commercialization proving large-scale liquid metal handling
Earliest viability: 5-7 years
Monitor: Prof. Michael Dickey, NC State (liquid metal electronics); Ambri (liquid metal batteries); Dr. Qian Wang, Chinese Academy of Sciences (gallium electrochemistry)
Membraneless Laminar Co-Flow Electrolyzer Array
EMERGING_SCIENCE3
Eliminate membrane by using laminar flow to keep products separate
Eliminates membrane failure mode entirely. Kjeang et al. demonstrated >1 W/cm² in membraneless fuel cells. If manufacturing scales, this could be the ultimate membrane-free architecture.
Manufacturing millions of parallel microchannels at acceptable cost is a major challenge. Clogging from seawater particles is serious concern. 3-5 year timeline and $5-20M development cost. The physics works; the manufacturing doesn't exist.
Trigger: Cost of microchannel arrays drops below $100/m² (currently ~$1000/m²), or 3D printing of metal microchannels becomes viable at scale
Earliest viability: 5-10 years
Monitor: Prof. Erik Kjeang, Simon Fraser University (membraneless fuel cells); Microchannel heat exchanger manufacturers (Heatric, Alfa Laval); MEMS foundries with high-volume capability
NiFe LDH + ALD-Protected Electrodes
EMERGING_SCIENCE4
Combine selective catalyst with atomic-layer protection for seawater durability
Both components are independently proven. Kuang et al. demonstrated >99% OER selectivity for 100+ hours. Díaz et al. demonstrated 10,000+ hour corrosion protection with ALD. The combination could achieve chlor-alkali efficiency in seawater.
Long-term NiFe LDH stability in real seawater (with organics, suspended solids) is less proven than lab demonstrations. ALD coating at electrode scale is more challenging than semiconductor wafers. Manufacturing integration is the gap.
Trigger: Publication demonstrating >1000 hours NiFe LDH stability in real seawater, or commercial ALD service offering electrode coating
Earliest viability: 2-3 years
Monitor: Prof. Hongjie Dai, Stanford (NiFe LDH catalyst development); Prof. Markus Antonietti, MPI Colloids (earth-abundant catalysts); ALD equipment manufacturers (Beneq, Picosun) for electrode-scale coating
Risks & Watchouts
What could go wrong.
Seawater variability (temperature, salinity, biology) may cause performance inconsistency across deployments
Design for operational flexibility; include sensors and adaptive control; test across multiple sites
Carbon credit pricing may not support $60-80/ton CO2 cost in near term
Target voluntary carbon market premium buyers (tech companies, airlines); pursue government procurement; design for cost reduction pathway
Ocean discharge of alkalinity or chlorine may face environmental permitting challenges
Engage regulators early; develop robust MRV (monitoring, reporting, verification); start with pilot permits in favorable jurisdictions
Offshore deployment and maintenance requires specialized marine operations capability
Partner with offshore wind or oil & gas operators; design for shore-based maintenance where possible
Polarity reversal frequency required for seawater may be so high that energy penalty exceeds 20%
Validate reversal protocol early in pilot; have fallback to chlorine-accepting architecture if penalty is unacceptable
Self-Critique
Where we might be wrong.
Medium
High confidence in the physics of polarity reversal and precipitation steering (proven in adjacent industries). Medium confidence in the economics (seawater is harder than brackish water; energy penalty may be higher than estimated). Lower confidence in the paradigm-shifting concepts (sacrificial Mg, NASICON) which have clear mechanisms but unvalidated economics.
Seawater may be fundamentally harder than brackish water—10,000x higher divalent cation load may overwhelm polarity reversal
The 5-15% energy penalty estimate for reversal may be optimistic; real penalty could be 20-30%
Sacrificial Mg economics may never work due to Mg cost and carbon footprint constraints
Regulatory barriers for ocean alkalinity enhancement may be higher than anticipated
Biological integration—cultivating beneficial biofilms rather than preventing all biofilms
Hybrid thermal-electrochemical approaches using waste heat to accelerate reactions
Capacitive deionization variants that shuffle ions without water splitting
Seawater may be fundamentally harder than brackish water
First validation step explicitly tests in seawater, not brackish water. 3-month exposure will reveal if polarity reversal is sufficient.
Energy penalty for reversal may be higher than estimated
Validation protocol includes energy consumption measurement. If penalty exceeds 20%, fallback to chlorine-accepting architecture.
Sacrificial Mg economics may never work
Parallel bench test on Mg anodes will validate dissolution rate, but full economics require lifecycle analysis including Mg sourcing. Recommend commissioning LCA if dissolution rate is promising.
Regulatory barriers may be higher than anticipated
Regulatory engagement is outside technical validation scope. Recommend parallel workstream on regulatory strategy, but this doesn't gate technical development.
Assumption Check
We assumed your constraints are fixed. If any can flex, here's what changes—and what to reconsider.
If passive approaches prove viable at scale, the entire electrochemical architecture may be unnecessary. Monitor Project Vesta and similar efforts.
The 'managed degradation' philosophy may extend further than we've proposed. Disposable electrolyzer cartridges replaced annually could beat hardened systems.
At $0.50/m³ desalination cost, pretreatment adds ~$5-10/ton NaOH—potentially acceptable if it enables proven chlor-alkali technology.
If regulatory framework permits <1 ppm Cl₂ in discharge, system design simplifies dramatically. This is a policy question, not a technical one.
Final Recommendation
Personal recommendation from the analysis.
If this were my project, I'd start with the boring stuff that works. Get an EDR system from Evoqua or Suez, modify it for seawater with more frequent polarity reversal (start at 15 minutes, optimize down to 5 if needed), and add precipitation steering targets upstream of the electrodes. This combination addresses both biofouling and mineral scaling with proven physics and minimal development risk. Run it for 3 months in real seawater and measure everything—electrode weight loss, surface morphology, electrochemical performance, fouling coverage. That's your baseline.
While that's running, I'd set up a parallel bench test on sacrificial Mg anodes. This is the paradigm-shifting concept that could change everything, and it's cheap to test. Buy some marine-grade Mg anodes from a cathodic protection supplier, put them in seawater with a cathode, and measure dissolution rate under various conditions. The key question is whether Mg(OH)₂ passivation can be managed. If you can sustain >5 mm/year dissolution with reasonable flow or current, you've got something. If passivation kills it, you've spent $20K to learn that and can move on.
The one thing I would NOT do is chase the exotic materials (NASICON, Galinstan, membraneless microchannels) until the simpler approaches hit a wall. Those are 5-year bets with major manufacturing uncertainty. The polarity reversal + modular cartridge approach can probably hit $80/ton CO2 with existing technology—that's the near-term path. Save the paradigm shifts for the next generation.