On October 9, 2026, Germany's Technical University of Darmstadt announced a new catalyst that lets zinc-air batteries charge and discharge stably for more than 300 hours. The catalyst combines iron and nickel oxide with a specially structured carbon material, and its durability was confirmed in prototype cells built in the laboratory.
What stands out about this result is not only the catalyst's chemical composition. The researchers also designed the material's microstructure so that the sites where oxygen and electrolyte react can be maintained over a long period. However, the figure of 300 hours is the total test time over repeated charge and discharge cycles. It does not mean the battery can run for 300 hours on a single charge.
The challenge for zinc-air batteries: two different oxygen reactions during charging and discharging
A zinc-air battery uses oxygen from the air in the reaction at its positive electrode. Because oxygen does not need to be stored inside the battery, it could achieve a high theoretical energy density, and it is being researched as one alternative to lithium-ion batteries for energy storage.
Rechargeable zinc-air batteries, however, face a major challenge: performance declines with repeated use.
During discharge, the positive electrode undergoes the oxygen reduction reaction (ORR), in which oxygen accepts electrons. During charging, the opposite process is needed: the oxygen evolution reaction (OER), which generates oxygen.
The two reactions differ in nature, and driving both efficiently is not easy. In particular, keeping the catalyst's performance intact through repeated charging and discharging is a key issue for extending battery life.
Materials that promote both reactions are called bifunctional catalysts.
The research team led by Professor Jörg J. Schneider at TU Darmstadt focused on an oxide called nickel ferrite (NiFe₂O₄).
Nickel ferrite is a compound of nickel, iron, and oxygen with a crystal structure known as spinel. It has long been studied as a material that promotes electrochemical reactions involving oxygen, but it has had problems with poor electron flow and with stability under repeated reactions.
Rather than trying to improve nickel ferrite on its own, the team combined it with a carbon material that carries electrons easily.
The key point is that getting electrons to the catalyst surface is not enough to make the reactions run efficiently.
At the air electrode of a zinc-air battery, three components must meet: the solid catalyst, the liquid electrolyte that carries ions, and gaseous oxygen. This contact region is called the three-phase interface, and it is where the electrochemical reactions of oxygen take place.
In its official announcement on October 9, TU Darmstadt also stressed the importance of keeping this three-phase interface stable.
Even if a catalyst is highly reactive, the battery cannot reach its potential unless enough oxygen and electrolyte reach it. Sustaining reactions over a long period requires both the catalyst's intrinsic properties and a structure that lets the necessary substances move in and out.
A new catalyst combining carbon nanohorns with nitrogen and phosphorus
The team developed a composite catalyst in which small cubic nickel ferrite particles are anchored to a carbon material called carbon nanohorns.
Carbon nanohorns are nanoscale carbon structures with horn-like pointed tips, and many of them gather to form spherical aggregates.
The interiors of these aggregates and the gaps between particles contain tiny spaces that can serve as pathways for oxygen and electrolyte to move through.
The researchers used this structure as the support for nickel ferrite. They also added nitrogen and phosphorus to the carbon nanohorns to tune the carbon's electronic state and surface properties.
The addition of nitrogen and phosphorus is intended to promote electron transfer and increase the number of active sites available for oxygen reactions.
Firmly fixing the nickel ferrite particles to the carbon structure is also expected to suppress particle aggregation and the dissolution of metal components into the electrolyte.
In other words, this study did not simply synthesize a new oxide. Its distinguishing feature is the integrated design of nickel ferrite, which promotes oxygen reactions, and carbon nanohorns, which help move electrons and reactants.
The carbon material carries electrons, and its fine spaces serve as pathways for oxygen and electrolyte. The aim is a structure that raises the catalyst's reactivity while maintaining performance through repeated charging and discharging.
The team also examined the material in detail after the long charge-discharge tests.
No nickel ions were detected in the electrolyte after use, and the iron concentration was about the same as in the electrolyte before use.
Electron microscope observation further showed that the cubic nickel ferrite particles anchored to the carbon material kept their shape, with no noticeable aggregation or structural collapse.
These results support the conclusion that the catalyst structure remained stable under the test conditions used.
However, this does not prove that metal dissolution or degradation will not occur under all operating conditions. Long-term stability under harsher conditions will need further verification.
Over 300 hours of charge-discharge demonstrated, but test conditions matter
The findings were published online on September 27, 2026, in the journal Advanced Science as a peer-reviewed paper by Sudheer Kumar Yadav and colleagues. The paper is titled "Nickelferrite on Pnictogen Functionalized Carbon Nanohorns. Bifunctional ORR and OER Catalysts in Rechargeable Zinc-Air Batteries" (DOI: 10.1002/advs.77749).
The durability of more than 300 hours was confirmed in a prototype cell that used the new catalyst in the air electrode and a zinc oxide-carbon composite (ZnO/C) as the negative electrode.
The electrolyte was a potassium hydroxide aqueous solution with a concentration of 4.0 mol/L.
In the test, the current density was set to 0.55 mA/cm², each charge-discharge cycle lasted three hours, and the cell was charged and discharged repeatedly at constant current.
As a result, the voltage gap between charging and discharging stayed nearly constant even after more than 300 hours of continued cycling.
This indicates that stable operation was maintained over roughly 100 cycles.
To reiterate, though, 300 hours is not the length of time the cell can supply power continuously. It is the total duration of the test over repeated charging and discharging. It is different from an indicator of the battery's storage capacity or of how long it can be used on a single charge.
The paper also reports a durability test of a different configuration that used zinc foil as the negative electrode.
This configuration achieved 250 hours of charge-discharge operation, but it differs not only in anode material but also in current density and cycle length.
Based on Figures 9 and 10 (pages 13–14) of the paper published by the research team, the two test conditions can be summarized as follows.
| Test condition | ZnO/C composite anode | Zinc foil anode |
|---|---|---|
| Current density | 0.55 mA/cm² | 5 mA/cm² |
| Duration of one cycle | 3 hours | 1 hour |
| Charge-discharge duration | Over 300 hours | 250 hours |
| Relevant figure in paper | Figure 9 | Figure 10 |
The zinc foil test used a current density of 5 mA/cm², higher than in the ZnO/C composite anode test.
For that reason, one cannot conclude from the 300-hour and 250-hour figures alone that the ZnO/C composite anode offers a longer lifespan.
Because current density and cycle conditions differ, the comparison does not isolate performance differences due solely to the anode material.
The two tests should each be assessed as results showing that the cell can be charged and discharged repeatedly under different conditions.
In addition, the prototype cell that achieved over 300 hours used a composite material not only in the air electrode's new catalyst but also in the negative electrode.
Battery lifespan depends on interactions among the positive electrode, negative electrode, electrolyte, and other components, so the improved durability of the whole cell cannot be attributed solely to the new catalyst.
Maximum power density about 1.9 times higher, but larger-cell validation is needed for practical use
The study compared not only charge-discharge durability but also the power the battery can deliver.
The maximum power density of the zinc-air battery using the new catalyst was 54 mW/cm².
By comparison, the precious-metal-based catalyst used as a reference reached 28 mW/cm².
The reference catalyst was a 1:1 mass-ratio mixture of a carbon-supported catalyst containing 20% platinum (Pt/C) and ruthenium oxide (RuO₂).
Based on polarization curves measured within the same study, the cell using the new catalyst showed a maximum power density about 1.9 times higher.
This suggests that a catalyst combining nickel ferrite and carbon nanohorns may improve the output performance of the battery as a whole.
Power density and energy density, however, are different measures.
Power density indicates how much electric power can be drawn per unit area of the electrode. Energy density, by contrast, indicates how much energy a battery can store.
The figure of 54 mW/cm² does not support the conclusion that the battery can supply more power for longer than a lithium-ion battery.
The new catalyst also did not outperform existing precious-metal-based catalysts on every metric.
For example, when the oxygen evolution reaction was measured in a 0.1 mol/L potassium hydroxide aqueous solution, the overpotential needed to reach a current density of 10 mA/cm² was 290 mV for the new catalyst.
The reference ruthenium oxide required 260 mV.
Overpotential is the voltage that must be applied beyond the theoretical voltage needed to drive an electrochemical reaction, and a smaller value is generally preferable.
On this OER metric, therefore, the new catalyst falls short of the reference ruthenium oxide.
In charging and discharging a zinc-air battery, however, performance is affected not only by the oxygen evolution reaction but also by the oxygen reduction reaction, the electrode structure, and how easily electrons flow.
For that reason, one must evaluate not just specific measurements of the catalyst alone but also output, charge-discharge efficiency, and durability when it is built into an actual battery.
Another expected advantage of this research is that it could yield a catalyst that does not depend on precious metals such as platinum and ruthenium.
A material composition centered on iron, nickel, and carbon could help reduce raw-material costs.
However, this study did not verify the processes needed for mass production of the catalyst or its manufacturing cost.
Actual production costs depend not only on raw-material prices but also on how carbon nanohorns are produced, the steps for adding nitrogen and phosphorus, and the cost of forming and anchoring the nickel ferrite particles.
Furthermore, the over-300-hour durability result comes from a small cell built in the laboratory.
For use as a practical storage battery, long-term durability at higher current densities, oxygen supply inside larger electrodes, and electrolyte management will also have to be verified.
Zinc-air batteries could take advantage of their high theoretical energy density and relatively accessible materials, but many technical challenges remain before they can be put to practical use as rechargeable batteries.
What this study shows is that designing the catalyst's chemical composition, which promotes oxygen reactions, together with a microstructure that carries electrons and reactants may improve charge-discharge performance and durability.
Charge-discharge operation exceeding 300 hours and a maximum power density about 1.9 times that of the reference catalyst are experimental results that support its effectiveness.
The next questions are whether performance can be maintained under harsher operating conditions, whether similar results can be obtained in larger cells, and how far manufacturing costs can be reduced.
Whether the new catalyst stays a laboratory achievement or leads to practical rechargeable zinc-air batteries will depend on accumulating this kind of verification.