Zinc-air batteries get dramatic boost from low-cost metal breakthrough
Researchers say they’ve found an efficient and cost-effective solution that could dramatically improve zinc-air batteries, a clean and safe energy storage option but, until now, has been hampered by performance issues.
The race to find high-density, cost-effective and environmentally friendly batteries is a major obstacle to achieving an electrified world, as most renewable energy sources, being intermittent, require good energy storage solutions. ‘energy.
Rechargeable zinc-air batteries are powered by oxidizing zinc with oxygen from the air. They are considered a possible candidate for next-generation energy storage because, in the theory, they could have an ultra-high energy density. Not only that, but they can be recycled, disposed of safely and recharged with new zinc.
Breaking down barriers to scaling technology
Zinc-air batteries are already used in hearing aids and some electric vehicles, but current examples tend to be hampered by slow electrochemical reactions, a major obstacle to scaling up the technology.
The problem lies in a pair of reactions, called oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), that occur at the air cathode during battery charging and discharging.
“Redox kinetics for ORR and OER are very slow and lead to severe polarization, reduced energy efficiency and limited life of practical rechargeable zinc-air batteries,” says study author Bo- Quan Li, associate professor at the Beijing Institute of Technology.
To solve the problem, Li and his co-authors looked at two families of metals, noble metals and transition metals (nickel, cobalt, manganese and iron), both of which can catalyze ORR and OER reactions by accelerating the transfer of electrons between the electrode and the reactants.
“Noble metal electrocatalysts demonstrate state-of-the-art electrocatalytic activity and serve as widely accepted benchmarks,” Li said. “But high cost, earth scarcity, and poor durability hinder their large-scale practical applications.”
Transition metals offer hope
Transition metals, on the other hand, include relatively abundant and inexpensive metals like iron (Fe) and nickel (Ni). The researchers combined these two transition metals and embedded the composite on a substrate; iron stimulated the ORR reaction, while nickel successfully stimulated the OER reaction.
“A single type of active site can hardly promote both ORR and OER kinetics simultaneously to provide outstanding bifunctional electrocatalytic activity,” says Li.
“The composition of different active sites with respective electrocatalytic activity has been verified as an effective strategy to achieve multifunctionality.”
In fact, their electrocatalyst performed better than previously demonstrated noble metal versions.
“The composite electrocatalyst demonstrated outstanding bifunctional electrocatalyst activity that outperforms the noble metal-based electrocatalyst and most reported bifunctional electrocatalysts based on analogous active sites,” Li said.
It’s a win-win: not only would an iron-nickel catalyst achieve high power density and long life, but both iron and nickel are abundant and cost-effective, providing energy storage without harming the planet or driving battery prices beyond feasibility.
The race to provide an efficient zinc-air system for energy storage is accelerating. Other researchers have addressed the zinc-air performance problem by introducing a photoactive catalyst to speed up the reactions. The American company Zinc8 has been producing a rechargeable zinc-air hybrid flow battery since 2020.
Amalyah Hart is a science journalist based in Melbourne.