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# Turning sun and seawater into disinfectant

Yaovi Holade, Mikhael Bechelany

► To cite this version:

Yaovi Holade, Mikhael Bechelany. Turning sun and seawater into disinfectant. Nature Sustainability, 2025, 8 (6), pp.586-587. 10.1038/s41893-025-01564-2. hal-05445901

HAL Id: hal-05445901

https://hal.science/hal-05445901v1

Submitted on 7 Jan 2026

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Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
Email: yaovi.holade@umontpellier.fr

Hypochlorite is in wide industrial and domestic use as disinfectant, but its manufacture, involving the processing and transport of hazardous chemicals, is problematic. Now a safer, more sustainable alternative, powered by sunlight and seawater, has been developed.

Sodium hypochlorite (NaClO) is manufactured industrially in large quantities and widely used for disinfection, bleaching and wastewater treatment<fnref n="1" />,<fnref n="2" />. Currently, the main means of production involves reacting prefabricated hazardous chemicals, namely sodium-hydroxide solution and chlorine gas, but this poses safety, cost and environmental issues in relation to materials, transport and storage. Writing in *Nature Sustainability*, Gao and colleagues<fnref n="3" /> present — in an experimental and computational tour de force — an innovative approach to hypochlorite production that combines solar energy, seawater and a visible-light-absorbing material to selectively transform seawater, and the sodium and chloride ions naturally present there, into hypochlorite. Furthermore, in their scheme, electricity consumption is drastically reduced and high-value products, such as green hydrogen, are co-generated.

Given that seawater naturally contains the constituents of sodium hypochlorite, it is logical to think of using seawater for the manufacture of hypochlorite. However, the manufacture from seawater of chlorine⁴ — with an electrolyzer, which uses electricity to split out the constituent elements — tends to be hindered either by the competitive process of water oxidation to oxygen⁵ or by the release of toxic chlorine gas. Instead, Gao et al.<fnref n="3" /> have developed an electrolyzer with a specially designed ‘photoanode’ (see Fig. 1). This alternative electrolyzer is powered by renewable electricity and supplied with seawater and solar energy. The photoanode steers competing reactions towards the conversion of chlorides to hypochlorite, while simultaneously co-generating hydrogen, magnesium hydroxide and calcium carbonate — all high-value chemicals. The photoanode is composed of niobium-oxide-modified bismuth vanadate with inserted chloride (NbClO/BiVO₄), which regulates

<footnote n="1">¹Institut Européen des Membranes, University of Montpellier, ENSCM, CNRS, Montpellier, France</footnote>

<footnote n="2">²Institut Universitaire de France, Paris, France</footnote>

<footnote n="3">³Functional Materials Group, Gulf University for Science and Technology, Mubarak Al-Abdullah, Kuwait</footnote>
the population of chloride and hydroxyl species on the photoanode surface to achieve their optimal
coupling to hypochlorite, thereby quenching unwanted recombination of neighbouring chlorides or
hydroxyls to form either chlorine or oxygen⁶.

Notably, this approach can 'freeze' the chloride inserted in the niobium-oxide-modified bismuth vanadate while ensuring efficient electron transfer by amplifying the ability, on one side, of the bismuth and vanadium species to lose electrons and, on the other, of the niobium to capture electrons. This effect has been corroborated by more than 500 hours of continuous operation: the chlorine present within the photoanode is not transferred into hypochlorite. Gao and co-workers also found that the presence of niobium oxide with inserted chloride and bismuth vanadate resulted in an ultrafast charge-transfer rate up to five times faster than the unmodified bismuth vanadate and a solar-to-hypochlorite conversion efficiency four times higher than the bismuth vanadate, meaning that all the electricity consumed by the electrolyzer was devoted to disinfectant production and ruling out parasitic production of chlorine or oxygen²,⁴⁻⁶. Their computations of 300 possible reaction sites revealed that bismuth bonded to niobium, at the $BiVO_4-NbClO$ interface inside the photoanode, are the optimal active sites.

Having tested the photoanode in simulated sunlight, Gao et al. have also demonstrated its — remarkably similar — performance under real sunlight in outdoor tests with seawater. Their findings underline the robustness of this electrolyzer in withstanding the harsh conditions of solar energy and seawater, going beyond most other reported attempts which tend to focus on the use of solar simulators⁷. The researchers have also tested the disinfection capability of their process, using representative pathogenic bacteria and a series of control experiments for validation⁸: bacteria incubated in the electrolyzed seawater solution demonstrated a sterilization rate of almost 100%.

A basic economic analysis, comparing this system with a commercially available, dimensionally stabilized anode in the classical configuration, revealed that producing the same amount of hypochlorite using the new photoanode reduces electricity costs by 77% and carbon dioxide emissions by 75%. In addition, at the cathode (based on platinum) 100% electricity-to-hydrogen-fuel conversion was achieved, along with precipitation of valuable magnesium hydroxide and calcium carbonate (owing to basicity increase triggered by water-molecule decomposition⁵). These results highlight the potential of the approach, but the technology is certainly open to further development to improve reaction conditions (with, for example, a cost-effective cathode and flow field) and drive its transition from basic to applied research, suitable for mass production⁹. Further refinement of the
photoanode structure is needed, to understand how the applied electrochemical conditions
influence the structure of the material and also the consequences of chloride occurring beyond the
targeted niobium-oxide host and penetrating deeply into the bismuth vanadate.

Gao and colleagues³ have certainly contributed outside-the-box thinking on the challenge of one-site manufacture of hypochlorite disinfectant. Their elegant, greener and safer approach ensures hazardous chemicals such as chlorine gas and sodium hydroxide no longer need to be prepared and transported over long distances, and also enables the co-generation of three other useful chemicals. Using abundant seawater and solar energy within an electrolyzer powered by renewable energy addresses sustainability — by offering versatility in terms of energy sources, location, environmental and economic facilities — and a means of meeting the growing demand for local manufacture of key commodity chemicals.

## References

1. Cheng, X. et al. *Sci. Total Environ.* **803**, 150085 (2022).

2. Karlsson, R. K. B. & Cornell, A. *Chem. Rev.* **116**, 2982–3028 (2016).

3. Gao, R.-T. et al. *Nat. Sustain.* https://doi.org/10.1038/s41893-025-01530-y (2025).

4. Zhao, S. et al. *Nat. Sustain.* **7**, 148–157 (2024).

5. Dresp, S., Dionigi, F., Klingenhof, M. & Strasser, P. *ACS Energy Lett.* **4**, 933–942 (2019).

6. Vos, J. G., Wezendonk, T. A., Jeremiasse, A. W. & Koper, M. T. M. *J. Am. Chem. Soc.* **140**, 10270–10281 (2018).

7. Ito, S. et al. *Sol. Energy Mater. Sol. Cells* **82**, 421–429 (2004).

8. Collivignarelli, M. C., Abbà, A., Benigna, I., Sorlini, S. & Torretta, V. *Sustainability* **10**, 86 (2018).

9. Siegmund, D. et al. *JACS Au* **1**, 527–535 (2021).

## Competing interests

The authors declare no competing interests.
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Fig. 1 | A co-generation electrolyzer powered by renewable electricity and supplied with seawater and solar energy produces disinfectant (hypochlorite), hydrogen fuel, magnesium hydroxide and calcium carbonate. Gao and colleagues³ have developed a photoanode using bismuth vanadate (BiVO₄) modified on its surface by niobium oxide with inserted chloride (NbClO). This absorbs visible light to selectively oxidize chloride ions in seawater — overcoming competing oxidation reactions — and generate hypochlorite (ClO⁻), which coexists with the sodium ions (Na⁺) and chloride ions (Cl⁻) present in seawater, resulting in a potent disinfectant. Meanwhile the platinum cathode decomposes water molecules to generate hydrogen (H₂), precipitating calcium and magnesium ions in the form of magnesium hydroxide (Mg(OH)₂) and calcium carbonate (CaCO₃).