Hydrogenated borophene with cobalt nickel compounds enables stable lithium hydroxide chemistry in water, activating oxygen sites for high energy storage and exceptional cycling performance in aqueous devices.
(Nanowerk Spotlight) Lithium batteries dominate phones, laptops, and electric cars, but their biggest weakness has little to do with lithium itself. The chemistry relies on organic electrolytes that are flammable and degrade over time. A safer alternative would be a battery that runs in water. In practice, water destroys most lithium-based chemistry. Add oxygen to the system, and the reactions become even less predictable. The compounds produced during discharge clog the electrodes and refuse to break apart again.
Researchers experimented with exotic additives and tailored catalysts, but the same pattern repeated: the chemistry worked once or twice, then failed, usually because oxygen produced the wrong reaction product.
Lithium hydroxide offered a possible escape route. It forms through a four-electron pathway that can, in principle, hold more charge per unit mass than lithium peroxide. It is also chemically more stable. The catch was making LiOH in a device that could charge and discharge reliably. The few successful demonstrations used nonaqueous electrolytes and special additives. Most attempts to run LiOH formation in water never made it past early tests. The oxygen intermediates reacted too fast or in the wrong direction, leaving behind debris and losing capacity.
The material they built is called HB/CoNiC. It is a composite of hydrogenated borophene and cobalt–nickel oxyhydroxides. Borophene is an ultra-thin sheet of boron atoms. When hydrogen is added to its surface, it becomes a strong electron donor. That matters because the surrounding cobalt and nickel absorb some of those electrons. They form small alloy particles rather than remaining fully oxidized. Around those particles, oxygen atoms no longer sit in their usual tightly bonded positions. Some of them become what chemists call “undercoordinated”: they are missing a bond. It sounds like a flaw, but it is precisely what the design needs. Those oxygens hold loose electrons and act as reaction sites.
a) Illustration of the electrochemical-electrophoretic deposition process and the electron energy levels of oxygen nonbonding states (ONB). b) Field emission scanning electron microscopy image of HB/CoNiC. c) Field emission transmission electron microscopy (FE-TEM, top) and energy dispersive X-ray spectroscopy (bottom) images of HB/CoNiC. d) High-resolution TEM (left) and magnified TEM images with fast Fourier transform (right) images in three different regions. e) X-ray diffraction patterns and f) Raman spectra. X-ray photoelectron spectroscopy (XPS) spectra in the g) B 1s and h) O 1s regions. (Image: Reproduced with permission from Wiley-VCH Verlag) (click on image to enlarge)
In most battery materials, oxygen stays in the background while the metal atoms do the work of storing and releasing charge. In HB/CoNiC, the oxygen becomes part of the work. The undercoordinated atoms can accept and release electrons without falling apart. They behave like flexible connectors that absorb and transfer charge between lithium, metal, and hydroxide. The borophene does not just sit at the surface. It reshapes the internal electronic landscape.
The team built the composite in layers. They electrochemically deposited cobalt–nickel oxyhydroxide onto carbon paper. Then they used an electrophoretic process to pull hydrogenated borophene into the structure. The result was a network of nanosheets with alloy particles embedded inside them. Microscopy and spectroscopy confirmed the alloying, the boron–hydrogen bonds, and the presence of undercoordinated oxygen. The key was not simply mixing the materials but forcing them into the right spatial and electronic arrangement.
They then tested the electrode in a water-based electrolyte containing two salts at equal concentration. One provided lithium ions. The other provided hydroxide ions. This dual environment allows two different reactions to occur at the same time: lithium insertion and proton transfer. Together, these reactions form LiOH during discharge and break it apart during charge. In the cobalt–nickel material without borophene, those steps never activated cleanly. In HB/CoNiC, they appeared sharply in the electrochemical data as distinct redox peaks.
The electrode behaved nothing like a conventional supercapacitor. Instead of storing charge mainly on its surface, it stored charge through fast chemical reactions at those oxygen sites. The researchers eventually built two HB/CoNiC electrodes into a device they describe as a supercapattery—a hybrid that charges quickly like a capacitor but stores energy with battery-like density. That device reached high energy output and maintained performance even under demanding cycling conditions.
The researchers tracked what was happening during charging and discharging. When the device charged, cobalt and nickel moved into higher oxidation states. Then something unusual occurred: the undercoordinated oxygens paired into O–O units. These dimers are short-lived intermediates that hold the reaction in a reversible state. During discharge, lithium ions attached to these pairs, forming Li₂O₂. That compound then protonated—essentially taking on hydrogen—to become LiOH. When the device charged again, the lithium hydroxide decomposed and the oxygen pairs re-formed, ready for another cycle. Nuclear magnetic resonance and X-ray spectroscopy confirmed the presence of LiOH only when the material was discharged. The control material showed no such chemistry.
Computer modeling explained why the cycle worked. In most cobalt or nickel systems, forming oxygen pairs is too costly. The reaction veers into dead ends that produce residues. In HB/CoNiC, the energy required for oxygen pairing is much lower. The undercoordinated oxygen atoms handle electron transfer more naturally, and the borophene reduces the surrounding metals so that the lattice can support those intermediates. The reaction moves through the intended four-electron pathway rather than collapsing into one- or two-electron dead zones.
The most striking aspect of this work is not the performance numbers, but the principle behind them. Rather than protecting lithium chemistry from water, the researchers embraced the features that made water difficult. They built a material that can use oxygen not as a structural bystander but as a genuine participant in storage. In doing so, they created a reversible cycle that has resisted aqueous lithium systems for years. It does not solve every challenge in energy storage. But it changes the conversation from “water is the problem” to “the electrode decides what water can do.”
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