Same Cheap Tubes GO Powers Both CDI Water Desalination and CapMix Salinity-Gradient Energy Harvesting

Sustainable freshwater supply and carbon-free electricity are two of the largest engineering problems of the next decade, and the boundary between them is electrochemistry. The Lamberti group at Politecnico di Torino has demonstrated, across two peer-reviewed papers two years apart, that the same functionalized Cheap Tubes graphene oxide can do both: 17 mg/g salt removal at 98% charge efficiency when run as a capacitive deionization (CDI) desalination electrode (Pedico et al., Advanced Materials Technologies 2022), and 12 mW/m² net power output when run as an asymmetric CapMix electrode harvesting energy from salinity gradients where freshwater meets seawater (Pedico et al., Advanced Sustainable Systems 2024). One material, two opposite directions of the same electrochemistry — the kind of dual-application demonstration that compresses R&D risk for buyers evaluating graphene oxide for water-energy systems.

The Research Context

Capacitive Deionization and Capacitive Mixing are two faces of the same physical principle — ion adsorption / desorption at high-surface-area electrodes in an aqueous electrolyte. Run the cycle in desalination mode (input electrical energy to drive salt ions onto the electrode, then discharge to release them) and you remove salt from water. Run the same architecture in CapMix mode (alternately expose the electrodes to high-salinity seawater and low-salinity freshwater, and the open-circuit voltage swing across the cycle drives current through an external load) and you harvest energy from the salinity gradient instead of consuming it. The electrode chemistry that makes one work efficiently is the same chemistry that makes the other efficient. The Lamberti group's Pedico-led work shows that the same Cheap Tubes single-layer GO, functionalized with a quaternary-ammonium acrylate monomer, performs at the front of the literature in both modes.

Materials and Methods (Common to Both Papers)

Graphene oxide — Cheap Tubes single-layer (300-800 nm lateral)

From the CDI 2022 paper (Materials section, verbatim): "GO flakes (single-layer GO, 300-800 nm of lateral dimension, Cheap Tubes Inc.) and PVDF powder … were dispersed in dimethyl sulfoxide."

From the CapMix 2024 paper (Materials section, verbatim): "GO flakes (Single layer GO, 300-800 nm of lateral dimension, CheapTubes Inc.) were functionalized following a two-step procedure described in previous work [28]." (Reference [28] points to the 2022 CDI paper — same material, same functionalization route, two applications.)

Functionalization route — quaternary-ammonium acrylate grafting

Pristine Cheap Tubes GO is functionalized in two steps with (2-(acryloyloxy)ethyl)trimethylammonium chloride, producing a positively charged graphene oxide surface (fGO+) that can be paired against carbon-black-based negative electrodes in the asymmetric configuration both papers exploit. The Lamberti group describes this as a "simple and scalable" route — no exotic reagents, no microwave or autoclave step, no surfactant exchange.

Electrode fabrication

• CDI 2022: fGO mixed with activated carbon and PVDF binder, coated onto metallic current collector.
• CapMix 2024: activated carbon coated with fGO and sulfonated poly(ether ether ketone) (SPEEK), assembled in an asymmetric architecture in a polymer-micromachined cell.

Key Results — CDI Mode (Pedico 2022)

The functionalized GO electrode reached ~17 mg/g salt adsorption capacity with a charge efficiency of 98%. Charge efficiency — the fraction of the electrical charge that goes into salt-ion adsorption rather than parasitic side reactions — is the metric that determines whether a CDI cell is energy-efficient enough to displace reverse osmosis at low salinity. 98% is at the top of the published range for capacitive deionization electrodes and improves measurably on activated-carbon-only baselines.

Key Results — CapMix Mode (Pedico 2024)

The CapMix device, with positively-charged functionalized GO on one electrode and sulfonated PEEK (negatively charged) on the other, delivered a net power output of 12 mW/m² by alternately exposing the cell to simulated seawater and freshwater — up to ~6× the power output of a symmetric activated-carbon baseline. The world's salinity-gradient resource is estimated at the terawatt scale (river mouths and coastal estuaries), so even modest per-area power outputs project to meaningful aggregate generation when devices are deployed at industrial scale.

Why the Same GO Works Both Ways

• The electrochemistry is symmetric. CDI applies external voltage to drive salt-ion adsorption; CapMix lets a salinity-driven open-circuit voltage swing drive current through an external load. The same electrode chemistry — high specific surface area + charge-selective surface functionalization — works for both directions.
• Cheap Tubes single-layer GO (300-800 nm lateral) delivers high SSA per gram and clean surface chemistry. Quaternary-ammonium functionalization grafts onto the abundant epoxy and hydroxyl groups on the GO basal plane, producing a uniformly positively charged surface that is selective for anions in solution.
• One functionalization route, two devices. The 2024 CapMix paper explicitly cites the 2022 CDI paper for the GO functionalization procedure (reference [28] in the CapMix paper). The same material, the same chemistry, the same supplier — just rewired for a different operating mode.

Application Areas

• Capacitive Deionization (CDI) desalination — brackish-water treatment, agriculture irrigation conditioning, mine-water treatment, and other low-salinity desalination markets where reverse osmosis is energetically inefficient.
• CapMix / Reverse Electrodialysis (RED) salinity-gradient energy harvesting — estuarine power plants, coastal renewable energy, off-grid coastal installations.
• Hybrid CDI-CapMix cycles — some research groups operate the same cell alternately as a desalination unit and as a CapMix harvester, using the same hardware investment for both functions.
• Membrane-CDI (MCDI) and electrodialysis — charge-selective functionalized GO is also competitive as the active layer in ion-exchange membrane composites for related electrochemical water-treatment processes.
• Trace-contaminant removal from water — GO-based electrodes / membranes also enable removal of BTX hydrocarbons, antibiotics, and heavy metals from wastewater (a related line of work from the same group).

Order the Cheap Tubes GO Used in This Study

The single-layer graphene oxide used by the Lamberti group at Politecnico di Torino — single-layer GO, 300-800 nm lateral dimension — is available directly from Cheap Tubes. Order the same specification: Single Layer Graphene Oxide. Other GO formats (powder, gel, reduced GO, larger lateral grades) are available in the Graphene Oxide product category. Research and production volumes, SDS / TDS / CoA included, custom dispersions on request.

Frequently Asked Questions

Citations

---