Researchers at Singapore’s government-led Agency for Science, Technology and Research (A*STAR) discovered that nanoparticles containing three different layers of material can boost the performance of zinc-air batteries.
Historically, zinc-air batteries are cheap and long-lasting. But the sluggish reaction between the water-based electrolyte and oxygen limits the battery’s voltage output and its performance at high current.
As a result, finding a catalyst to speed up the reaction could yield higher power and energy densities, thus opening up more applications.
In response, researchers developed a nanoparticle catalyst. The particles are 20-50 nm across, with a cobalt core encased by an inner shell of cobalt oxide (Co3O4) and surrounded by an outer shell of pyrolyzed polydopamine (PPD)—a form of carbon “dotted” with nitrogen atoms.
These nanoparticles coat a porous carbon support that acts as an electrode. Their structure helps prevent them from leaching cobalt or clumping together, and the protective outer shell boosts durability.
These three-layer nanoparticles transform oxygen to hydroxide in a single step. Researchers suggest nitrogen atoms in the PPD shell help attract and make oxygen atoms more reactive on their way to catalytic sites in the cobalt oxide and PPD. Meanwhile, the cobalt core and PPD shell help electrons flow efficiently to the oxygen atoms.
In contrast, particles containing only cobalt and cobalt oxide, or only PPD, transformed oxygen in a two-step process that produced hydroperoxide, a corrosive intermediate.
The researchers tested their electrode in a zinc-air battery and found that it produced a current of five mA/cm2 of electrode at 1.36 V for five days, outperforming an electrode that relied on a conventional platinum catalyst. Their next step is to facilitate large-scale synthesis of the nanoparticles.
Source: A*STAR, research.a-star.edu.sg.