Seawater Electrolysis Enables Multipathway Climate Change Mitigation through Atmospheric Carbon Dioxide Removal, Renewable Hydrogen Production, and Cement and Concrete Decarbonization

[Geoengineering News]

https://pubs.acs.org/jacsat/article/doi/10.1021/jacs.6c13870/5430630

Authors: Xin Chen; Dale Prentice; Ross Arnold; Aaron Sabin; Camly Tran; Steven Bustillos; Adriano Leão; Marie Collin; Nicolas Alfonso Vargas; Mathieu Bauchy; Aditya Kumar; Narayanan Neithalath; Venkatasubramanian Viswanathan; Thomas Traynor; Lorenzo Corsini; Dante Simonetti; Torben Gadt; David Jassby; Fabian Rosner; Gaurav Sant; Erika La Plante 

15 September 2026

Abstract

Thermodynamically favorable (“downhill”) reactions that convert carbon dioxide (CO2) into stable solid and dissolved carbonates via reaction with alkaline materials offer a promising route to immobilize gigatonnes of CO2 drawn from dilute sources such as the atmosphere, oceans, and low-concentration flue gases. While subsurface geological CO2 mineralization is technically viable, it depends on specific geological conditions, water availability, and, critically, the availability of unbuilt infrastructure (e.g., pipelines, monitoring stations) and access to concentrated CO2, whose separation from dilute sources is both energy- and cost-intensive. Considering the dual need to remove CO2 from the atmosphere and to decarbonize emission-intensive industries, this perspective highlights electrolysis-driven pH-swing approaches that (a) accelerate CO2 removal from air or flue gases, with overall economics strengthened by the coproduction of hydrogen (H2), and (b) enable low-carbon cement (and hence, concrete) production. First, we present a seawater electrolysis strategy that enables atmospheric carbon dioxide removal (CDR) and produces (Ca,Mg) carbonates/hydroxides and H2 for a gross energy intensity (gEI) of ∼2 MWh per tonne of CO2 (MWh/tCO2). Here, key considerations include acid management and the mitigation of chlorine evolution at scale. Second, we highlight electrochemical methods to synthesize portlandite (Ca(OH)2) and H2 at ambient temperature and pressure from calcium-rich minerals and industrial residues, at ∼2 MWh per tonne Ca(OH)2. We discuss efficient means for calcium extraction and electrolytic Ca(OH)2 precipitation as critical aspects of this pathway. Collectively, these electrolysis-based methods offer scalable, energy-efficient solutions for gigatonne-scale CDR and “hard-to-abate” industrial sectors, particularly when powered by renewable energy.

Source: ACS PUBLICATIONS 

[Michael Hayes]

Many thanks to Geoengineering News for highlighting this exceptional piece of work from Chen et al.. The authors have provided our community with an incredibly rigorous thermodynamic and kinetic blueprint for leveraging downhill mineralization paths to capture gigatonne-scale CO₂. Their success in mapping a gross energy intensity of ~2 MWh/tCO2 sets a vital benchmark for the marine CDR sector.

As we look toward translating these critical chemical equations into scalable field deployments, we can build directly upon the boundaries outlined by the authors. By taking the paper’s core electrochemical mechanism and moving the operational boundary inside a free-floating subwave refinery using 100m enclosed HDPE reactor hulls stationed in an oceanic gyre, we can directly address the practical engineering bottlenecks—such as chlorine evolution (ClER) and outgassing—that the authors rightfully flag as major scale headaches, and more.

Below is an engineering framework demonstrating how this enclosed, co-product-driven architecture optimizes and operationalizes the pathways discribed by the authors:

1. Volumetric vs. Diffuse dMRV (Solving the Registry Uncertainty Discount)

Uncontained open-water frameworks or coastal outfalls rely heavily on complex hydrodynamic tracer modeling to infer atmospheric drawdown across shifting surface layers, which typically forces registries to apply steep uncertainty discounts to generated credits. By enclosing the electrochemical loops within 100-meter-long, high-density polyethylene (HDPE) hulls, we establish a closed system boundary. Measuring the alkalinity directly at sealed intake and outtake gates provides a precise, volumetric ledger. Coupled with an integrated surface snorkel and sea-air induction system, we can verify direct gas stripping and mineralization internally before the water is ever returned to the ambient ocean layer.

2. Thermal Mitigation (ΔT = 0) to Maximize Air-Sea Gas Exchange

Large-scale electrolysis loops inherently introduce Joule heating from electrical resistance. Discharging even slightly warm alkaline effluent into the open sea lowers CO₂ solubility (Henry's Law), raising local pCO₂ and delaying or blocking atmospheric carbon drawdown until the thermal plume dissipates. We utilize deep thermocline water intakes alongside passive skin-effect radiative cooling across the vast surface area of the 100m hulls. This ensures that the high-alkalinity discharge hits the exact ambient surface temperature equivalent at the exit gate, allowing the plume to remain stratified in the top-meter air-sea boundary layer for maximum, uninhibited atmospheric drawdown kinetics.

3. In-Situ Chlorine Scrubbing via Freshwater Azolla Aquaponics

To address the chlorine evolution (ClER) bottlenecks highlighted in the paper, the enclosed subwave hull routes the acidic, chlorine-bearing water from the anode compartment, and Biorock operations, directly into a fresh Azolla harvesting stream. The Azolla floating fern—cultivated within a strictly freshwater, cold-water RAS aquaponics loop alongside premium, high-Omega-3 finfish (like Landlocked Atlantic Salmon or Rainbow Trout)—possesses a rigid macromolecular structure rich in reactive polyphenols and lignin. These aromatic groups act as a highly effective chemical sponge, capturing free chlorine species via spontaneous electrophilic substitution and neutralizing them before any open-ocean discharge.

Furthermore, utilizing a freshwater biotic loop below the waves creates an absolute, fail-safe environmental barrier. In the event of a structural breach, the freshwater biota experiences immediate osmotic shock and dies off instantly in the surrounding 35‰ salinity open ocean, eliminating any risk of genetic or ecological contamination.

4. Autogenous Polymer Cracking Loops

In the subsequent sub-critical Hydrothermal Liquefaction (HTL) phase (280°C–350°C at 15–20 MPa), the organically bound chlorine acts as an in-situ acid catalyst, accelerating biomass hydrolysis. The halogens cleanly split from the hydrocarbon fragments and bind with ambient seawater cations (forming inert minerals like CaCl₂), leaving a pristine, halogen-free bio-crude oil as the sub-critical water phase cleanly partitions the stripped chlorine into inert inorganic salts via structural cation binding. This bio-crude can be catalytically cracked directly on the platform into the HDPE polymer needed to autonomously patch, reinforce, and expand the refinery's own structural hulls.

5. Native Mineral Generation via Biorock Electro-Mineral Accretion

The authors emphasize the massive logistical demand for alkaline materials and mineral inputs to sustain large-scale pH-swing loops. To eliminate the need for terrestrial mineral supply chains, the refinery integrates Biorock electro-mineral accretion as a low-tech, on-site generator of critical minerals. By running a low-voltage DC current through an internal structural mesh, the system triggers localized high-pH zones that precipitate thick, accessible layers of calcium carbonate (aragonite) and magnesium hydroxide (brucite) directly from seawater. This autogenous mineral pool supplies the necessary alkaline buffers for the fish-farming pools and provides the exact metal-hydroxide catalysts required to maximize oil yields in the downstream hydrothermal liquefaction and carbonization processing lines. Any outgassing from Biorock production can be fed into the biomass HTL/HTC processing loops.

---

This enclosed, freshwater-aquaponics modification aims to provide a reliable structural envelope for the authors' groundbreaking chemistry—resolving open-ocean containment risks, minimizing registry uncertainty discounts, and turning competitive anodic byproducts into a self-replicating material asset.

I would love to get the group's thoughts on how this closed-system boundary might alter your own deployment models for electrochemical OAE.

Warm regards,

--
You received this message because you are subscribed to the Google Groups "Carbon Dioxide Removal" group.
To unsubscribe from this group and stop receiving emails from it, send an email to CarbonDioxideRem...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/CAHJsh98boX4uC2xn4hZBr597EF%3DTcM6hj%3DVWxoxKkqAp%3DeQDLg%40mail.gmail.com.

[Michael Hayes]

The attached images show contained subsurface processing units. The large high density polyethylene hulls can be largely self-replicating using captured CO2 and oceanic nutrient inputs.

Apologies for the second post.

On Sun, Sep 20, 2026, 3:36 AM Geoengineering News <geoengine...@gmail.com> wrote:

--