Vitamin B12 Works as a Catalyst in Rechargeable Zinc-Air Batteries, Spanish Researchers Show

Vitamin B12, widely known as a dietary supplement, is drawing attention as an electrode catalyst for next-generation batteries. The FQM-204 physical chemistry research group at the University of Córdoba's Institute for Inorganic and Nanochemistry (IQUEMA) in Spain, together with collaborators, has developed a technique that covalently bonds vitamin B12 molecules to the surface of single-walled carbon nanotubes (SWCNTs) and uses the result as an air-electrode catalyst in rechargeable zinc-air batteries. The work shows that the molecular structure can be immobilized without high-temperature decomposition, and that it can promote the electrode reactions needed for both charging and discharging. The results were published in the Royal Society of Chemistry's peer-reviewed journal Journal of Materials Chemistry A. The paper was received on April 1, 2026, accepted on July 11, and published online on July 13 (DOI: 10.1039/D6TA02773C).

This is not, however, a battery that generates power by using vitamins as fuel. A zinc-air battery uses metallic zinc as the negative electrode and oxygen at the air electrode (the positive electrode). The research team used the cobalt complex in the vitamin B12 molecular structure as a catalyst. Specifically, it promotes the oxygen reduction reaction (ORR) during discharge and the oxygen evolution reaction (OER) during charging. The chemical reactions that store the battery's energy are driven by zinc and oxygen; vitamin B12 is incorporated as a material that lowers the overpotential required for the electrode reactions.

Zinc-air batteries have a high theoretical volumetric energy density, and using an aqueous electrolyte avoids the risks associated with flammable electrolytes, which is why they have been seen as promising for applications such as stationary energy storage. However, both the oxygen reduction and oxygen evolution reactions at the air electrode are slow, so efficient charging and discharging require a bifunctional catalyst that promotes both. Research has so far focused on expensive noble-metal catalysts such as platinum and iridium oxide, as well as catalysts made by heat-treating transition metals with carbon materials. The distinguishing feature of this study is that a metal complex that functions in living organisms was anchored to a carbon material with its molecular structure intact, and put to work as a catalyst while limiting its dissolution into the electrolyte.

Anchoring vitamin B12 to nanotubes to promote oxygen reactions

Cyanocobalamin, a form of vitamin B12, has a macrocyclic structure called a corrin ring with a cobalt atom at its center. This cobalt complex could potentially serve as a catalyst for reactions involving electron transfer, but vitamin B12 is highly soluble in water. Simply mixing it into an electrode material would let it dissolve into the electrolyte, making it difficult to keep it working as a catalyst over a long period. A method was therefore needed to fix it to the electrode surface while preserving the molecule's catalytic activity.

The team used single-walled carbon nanotubes with carboxyl groups introduced on their surface, and formed covalent bonds between them and vitamin B12. Specifically, they carried out a carbodiimide reaction using EDC and NHS in a phosphate buffer at pH 6.5, anchoring the B12 molecules to the nanotube surface through amide bonds. After the reaction, unreacted material was washed away and the product was dried at 40°C for three days to obtain the composite "VitB12-SWCNT." Unlike conventional catalyst production, which involves firing at high temperatures, this method has the advantage of leaving the vitamin B12 molecular framework intact without thermal decomposition.

The resulting material was analyzed using high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), resonance Raman spectroscopy, and other techniques, confirming that the cobalamin framework was anchored to the nanotube surface. In addition, resonance Raman spectra in alkaline electrolyte suggested a change to a "base-off" structure, in which the 5,6-dimethylbenzimidazole group, the lower axial ligand of the B12 molecule, is displaced from the cobalt center. In this structure, the cobalt atom is thought to be slightly exposed from the plane of the corrin ring, making it easier for oxygen molecules and reaction intermediates to bind. The team believes this change in molecular structure contributes to the improved catalytic activity.

Catalytic performance was evaluated in a three-electrode setup using a rotating ring-disk electrode (RRDE) in 0.1 M potassium hydroxide (KOH) aqueous solution saturated with oxygen. Compared with unmodified SWCNTs and non-immobilized vitamin B12 at a rotation speed of 1600 rpm, VitB12-SWCNT showed an oxygen reduction onset potential shifted more positive and a larger limiting current density. The onset potential was reported as about +0.85 V versus the reversible hydrogen electrode (RHE), with an experimental overpotential of about 0.38 V. The number of electrons transferred in the reaction was estimated at about 4, consistent with oxygen being reduced mainly through a four-electron pathway.

For the oxygen evolution reaction needed during charging, on the other hand, an overpotential of 0.77 V was required to reach a current density of 10 mA cm⁻². This is larger than the 0.45 V of the commercial cobalt oxide (Co₃O₄) nanoparticles used as a comparison, so for oxygen evolution alone it falls short of the inorganic oxide catalyst. It nonetheless showed clearly higher activity than unmodified SWCNTs, confirming that a single composite material can promote both oxygen reduction and oxygen evolution. In other words, it did not surpass existing high-performance catalysts across the board, but the work demonstrates that a bifunctional catalyst based on vitamin B12 is viable.

The team also examined the reaction mechanism using density functional theory (DFT). The calculations used a simplified model in which the axial ligand, ribose, phosphate group, and other parts of the B12 molecule were reduced. The results suggested that the oxygen reduction reaction can proceed at the Co(III) site without the cobalt center first being reduced from trivalent to divalent. However, this is a reaction pathway derived from a computational model, not one confirmed by directly observing each reaction intermediate on an actual electrode surface.

Charge-discharge demonstrated in small zinc-air cells; capacity figures need careful reading

Following the electrochemical measurements, the team assembled zinc-air batteries using VitB12-SWCNT as the air-electrode catalyst and evaluated their power output and discharge capacity. In interpreting the figures reported here, however, it is necessary to distinguish the configuration of the experimental cells from the mass by which discharge capacity is divided. In particular, specific capacity based only on catalyst mass differs greatly from the storage performance per weight of a finished battery.

The liquid-electrolyte cell used in the experiments was a small cell with an effective electrode area of 1.1 cm², using 1 mL of 6 M KOH aqueous solution as the electrolyte. A 0.5 mm-thick zinc plate served as the negative electrode, and carbon cloth was used as the gas diffusion layer of the air electrode. The mass of VitB12-SWCNT catalyst coated on the carbon cloth was 0.625 mg. The total mass of the air electrode, including the current collector and gas diffusion layer, was about 48.28 mg, roughly 77 times the mass of the catalyst itself.

This liquid-electrolyte cell had a maximum power output of about 30 mW, exceeding the roughly 25 mW of a control cell using unmodified SWCNTs. The result indicates that immobilizing vitamin B12 improved air-electrode performance, but what was measured is a small, milliwatt-class experimental cell. Whether similar performance can be obtained in practical systems with large-area electrodes or multiple cells combined has not been verified.

In the discharge capacity measurement, the cell was discharged at a constant current of −1 mA to the cutoff voltage, and a total discharge charge of 124.6 mAh was recorded for the whole cell. The team divided this charge by the catalyst mass of 0.625 mg and calculated a specific capacity of 199.4 Ah g⁻¹ (199,400 mAh g⁻¹) at a specific current of 1.6 A g⁻¹. The paper also lists a value based on the total air-electrode mass of about 48.28 mg: 4.13 Ah g⁻¹ (4,130 mAh g⁻¹) at a specific current of 0.021 A g⁻¹.

However, there is an arithmetic inconsistency in these specific capacities as stated in the paper. Dividing the discharge charge of 124.6 mAh by the total air-electrode mass of 48.28 mg gives about 2.58 Ah g⁻¹, which does not match the 4.13 Ah g⁻¹ given in the paper. Moreover, the ratio of the total air-electrode mass to the catalyst mass is about 77, but the ratio of the two stated specific capacities is only about 48. The paper does not specify the calculation steps or correction conditions that explain this difference, so 4.13 Ah g⁻¹ should be treated as a value published in the paper and distinguished from the value obtained by simple calculation from the same discharge result.

More important still, the value of 199.4 Ah g⁻¹ uses only the catalyst mass as the denominator, not that of the whole battery. Including electrode components other than the catalyst reduces the specific capacity sharply, and basing it on the mass of the entire cell, including the zinc negative electrode, electrolyte, and casing, would lower it further. Directly comparing this figure with the specific capacity of a few hundred mAh g⁻¹ of commercial lithium-ion battery electrode materials therefore says nothing about the performance gap as practical batteries. In addition to the liquid-electrolyte cell, the team also built a quasi-solid-state cell using a gel electrolyte combining polyvinyl alcohol (PVA) and KOH, and confirmed that it can charge and discharge in a flexible cell structure.

{
  "type": "bar",
  "title": "Air-electrode discharge capacity by normalization basis",
  "unit": "Ah/g",
  "categories": ["Normalization basis for discharge capacity"],
  "series": [
    {
      "name": "Catalyst mass basis (0.625 mg)",
      "values": [199.4]
    },
    {
      "name": "Calculated value on total air-electrode mass basis (48.28 mg)",
      "values": [2.58]
    }
  ],
  "caption": "Calculated from a discharge test at a constant current of −1 mA (total charge 124.6 mAh). Including electrode components other than the catalyst sharply reduces the specific capacity. The 4.13 Ah/g based on total air-electrode mass stated in the paper does not match the value calculated from these conditions.",
  "source": "Journal of Materials Chemistry A 14 (2026), 34201–34213"
}

"250 cycles of durability" does not mean 250 full charge-discharge cycles

The study also reports results from charge-discharge tests spanning around 250 cycles. However, the durability of a rechargeable battery cannot be judged by cycle count alone; conditions such as charge-discharge current, the charge per cycle, and depth of discharge must be checked. In particular, this test was not a full charge-discharge that uses a large share of the battery's capacity, but a shallow test that repeatedly cycled only a small fraction of it.

Specifically, the charge-discharge current was set to ±2 mA, and the charge per cycle was limited to 0.2 mAh. This corresponds to 6 minutes of discharge and 6 minutes of charge, and is only about 0.16% of the single-discharge capacity of 124.6 mAh described above. The cycle life reported here must therefore be distinguished from results of deep-cycle tests, in which a battery is discharged deeply and then recharged.

In cells using liquid 6 M KOH electrolyte, the control cell with unmodified SWCNTs lost its ability to hold voltage after 100 cycles, whereas the VitB12-SWCNT cell maintained a discharge voltage of 1.0 V or higher over 180 cycles. In the quasi-solid-state cell using PVA-KOH gel electrolyte, the unmodified SWCNT control cell could no longer sustain charging and discharging by the second cycle, while the VitB12-SWCNT cell operated for far longer. According to the paper's detailed description, the gel cell showed stable behavior over 225 cycles, maintaining a discharge voltage of 1.0 V or higher at 180 cycles and 0.9 V or higher at 235 cycles. The 0.2 mAh moved in and out per cycle under these conditions corresponds to 320 mAh g⁻¹ on a catalyst-mass basis.

The main measurement results and caveats for evaluating them are summarized below.

The paper's summary section and the University of Córdoba's announcement use phrases such as "durability of more than 250 cycles" or "up to 250 cycles." This does not mean, however, that the initial voltage and capacity were maintained through 250 charge-discharge cycles. The detailed measurements show that the discharge voltage stayed at 1.0 V or higher up to 180 cycles, fell to 0.9 V or higher by 235 cycles, and the cell continued to operate to around 250 cycles.

Still, given that the unmodified SWCNT control cells degraded early, the large improvement in charge-discharge stability from immobilizing vitamin B12 is an important result. At the same time, because the tests used shallow conditions that barely draw on the battery's capacity, they do not demonstrate the deep charge-discharge or thousands-of-cycles durability that matter for practical batteries. Comparing cycle counts alone with existing rechargeable batteries, without accounting for differences in test conditions, would not be appropriate.

Degradation stems from byproduct buildup on the electrode, not catalyst breakdown

To investigate why performance declined over long-term cycling, the team analyzed the electrodes after testing using XPS and SEM-EDX, which combines scanning electron microscopy with energy-dispersive X-ray spectroscopy. The results showed that the cobalt complex derived from vitamin B12 remained on the electrode surface, suggesting that decomposition of the catalyst molecule itself or its dissolution into the electrolyte is unlikely to be the main cause of degradation. Instead, byproducts deposited on the electrode surface were found to be interfering with the catalyst's function.

In zinc-air batteries that use an alkaline electrolyte, "zinc species crossover" occurs, in which zincate ions (Zn(OH)₄²⁻) generated at the negative electrode migrate toward the air electrode. In addition, when carbon dioxide in the air is absorbed into the KOH electrolyte, carbonate formation proceeds. The post-test analysis also found deposits containing potassium carbonate, zinc oxide, and other compounds on the air-electrode surface. These byproducts are thought to form a passivation film that covers the catalytic sites on the nanotube surface, hindering the movement of oxygen and ions.

This result supports the idea that anchoring vitamin B12 molecules by covalent bonds helps retain the catalyst on the electrode. On the other hand, even if the catalyst molecules are stable, covering the electrode surface with byproducts degrades the performance of the battery as a whole. Practical use will therefore require not only higher catalytic activity but also designs that suppress zinc species migration and carbonate formation and maintain the oxygen supply to the air electrode. Under deeper charge-discharge or long-term operation open to the atmosphere, zinc dendrite growth and evaporation of water could also become problems, so how much lifetime can be secured in real-world conditions will need to be verified.

The performance evaluation also has limitations tied to the experimental scale. The main cell characteristics in the paper are presented as measurements from individual experimental cells, and neither statistical reproducibility across multiple cells nor error ranges showing variation in the measurements are stated. Synthesis of the catalyst material remains at laboratory scale of under a gram, and production methods for large-area electrodes, costs at mass production, and long-term environmental impact have not been examined. Independent replication by third parties has not been shown either, so questions of performance reproducibility and manufacturing challenges remain on the path to practical use.

The University of Córdoba's official announcement also presents an outlook in which zinc-air batteries could become an energy storage technology that is lighter, safer, lower in cost, and lower in environmental impact than lithium-ion batteries. However, this describes the theoretical advantages and future potential of zinc-air battery technology as a whole; it does not mean the experimental cells in this study achieved performance exceeding existing lithium-ion batteries. A direct advantage over commercial batteries in whole-battery energy density, charge-discharge efficiency, lifetime, and manufacturing cost has not yet been demonstrated.

The value of this result lies in showing that vitamin B12, an organometallic complex, can be fixed to a carbon electrode with its molecular structure intact and used for both oxygen reduction and oxygen evolution. An electrode design that exploits molecular structure and catalytic function without relying on high-temperature treatment could offer a new option for developing non-precious-metal catalysts. To advance this into a practical rechargeable battery, however, it will be necessary to verify durability under deep charge-discharge conditions, prevent passivation film formation, and assess energy density at the level of the whole cell, including the electrodes and electrolyte. The next focus of the research is whether the catalyst's advantages, confirmed at the molecular level, can be maintained in an actual battery system.