EPFL-led team builds a water-based supercapacitor from clay and graphene
Researchers report a water-based supercapacitor that uses clay, graphene and confined water as its sole electrolyte, stable over 60,000 charge cycles.
Photo by liu lei on Pexels
Researchers led by EPFL in Switzerland have built a water-based supercapacitor that stores electrical charge using only clay, graphene and water, with no conventional liquid electrolyte. The device, which the team calls a “blue capacitor”, is described in the study “All-water supercapacitor enabled by 1-nm clay channels”, published in the journal “Nature Communications” on 5 June 2026. It held charge across more than 60,000 charge–discharge cycles with no detectable degradation, and reached an energy content the authors describe as comparable to commercial supercapacitors.
The work was carried out by Vasily Artemov, Aleksandra Radenovic and colleagues, with co-authors at the Austrian Institute of Technology, Hamburg University of Technology, the DESY synchrotron in Hamburg, and the Massachusetts Institute of Technology. The paper appears as Nature Communications volume 17, article 5014, with the identifier 10.1038/s41467-026-73924-1.
How the water-based supercapacitor works
The water-based supercapacitor is built from layered natural clay and conductive graphene, assembled into a single film by vacuum filtration. Stacking the materials produces channels about one nanometre wide. Water drawn into those channels acts as the only electrolyte, replacing the concentrated salt solutions or organic solvents used in conventional devices.
The film is a three-layer “membrane-electrode unit”: two graphene–clay electrodes separated by a layer of pure clay, between 100 and 200 micrometres thick in total, with the one-nanometre water channels running continuously through all three layers. Two graphite collectors are attached to the outside to carry current.
Inside the one-nanometre channels, water behaves differently from ordinary bulk water: it conducts protons quickly and stores charge at the graphene surface through a process the study attributes to electrical double-layer capacitance. The team reports that drying the film cuts its capacitance by orders of magnitude, and that rehydrating it restores the response, evidence that the confined water, not the dry clay frame, does the work.
What the device can and cannot do
The reported numbers place the blue capacitor in the range of existing supercapacitors rather than high-capacity batteries. The study measures a stable operating voltage of up to 1.6 ± 0.1 volts, a specific capacitance of up to 40 farads per gram, and 97 ± 2% coulombic efficiency.
| Property | Reported value |
|---|---|
| Stable operating voltage | up to 1.6 ± 0.1 V |
| Specific capacitance | up to 40 F g⁻¹ |
| Coulombic efficiency | 97 ± 2% |
| Cycling stability | more than 60,000 cycles, no detectable degradation |
| Specific energy | about 10 Wh kg⁻¹ of electrode material |
| Film thickness (electrode–separator unit) | 100–200 μm |
| Optimal graphene content in electrodes | about 35% |
All figures from Artemov et al. (2026), “All-water supercapacitor enabled by 1-nm clay channels”, Nature Communications.
One result the authors single out is the voltage window. Bulk water normally breaks down through electrolysis at about 1.23 volts, which limits water-based devices. In the one-nanometre channels, the team measured an electrolysis threshold of 1.6 ± 0.1 volts, leaving a wider usable range before the water splits.
The study is a laboratory demonstration. The authors report a specific energy of about 10 watt-hours per kilogram of electrode material, which they describe as comparable to commercial supercapacitors, and note that thinning the clay separator to cut resistance is limited by short-circuiting and needs further work. They do not claim battery-level energy density, and they do not report large-format cells or manufacturing costs.
Why a water-only electrolyte matters for sustainability
Most batteries and supercapacitors rely on concentrated electrolytes, organic solvents or metal oxides, which the authors note can limit sustainability and scalability. The blue capacitor instead uses clay and graphene, both abundant, and water, with electron microscopy detecting only the core clay atoms — oxygen, aluminium and silicon — plus carbon from graphene. The team links the long cycle life to this purity, because the absence of side reactions avoids the electrode corrosion that ages other devices.
Low-cost, non-toxic storage built from common materials is relevant well beyond the laboratory. Storage is often raised as the answer to the question of whether renewable energy is unreliable due to intermittency, and the cost and materials of batteries feed into the slow adoption of electric vehicles versus combustion engines. A device that swaps scarce or hazardous components for clay and water is aimed at that gap, though supercapacitors and batteries serve different roles: supercapacitors deliver and absorb power quickly over many cycles, while batteries store more energy for longer.
Background
The device builds on a decade of research into how water behaves when squeezed into spaces a few molecules wide. Experiments reported since the late 2010s found that nanoconfined water can have an unusually low dielectric constant and can conduct protons far faster than bulk water, hinting that it might carry charge without a conventional electrolyte. Natural clays such as montmorillonite swell to form roughly one-nanometre water layers when wet, giving researchers an abundant, self-assembling host for those channels.
Earlier studies were mostly confined to nanoscale test structures that are hard to reproduce or scale. The EPFL-led team’s contribution is a macroscopic, free-standing film that uses confined water as its sole electrolyte. An earlier version of the work was posted as a preprint, titled “Bulk electricity storage in 1-nm water channels”, before peer review. With the peer-reviewed paper now published in “Nature Communications”, the authors frame the blue capacitor as a platform for exploring sustainable, water-based energy storage rather than a finished product, leaving cost, scale-up and energy density as the open questions.
Sources: Nature Communications; arXiv (preprint)
Featured image: photo by liu lei on Pexels (free Pexels license).
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I specialize in sustainability education, curriculum co-creation, and early-stage project strategy. At WINSS, I craft articles on sustainability, transformative AI, and related topics. When I’m not writing, you’ll find me chasing the perfect sushi roll, exploring cities around the globe, or unwinding with my dog Puffy — the world’s most loyal sidekick.
