Design of a sectionalized MnO₂-Co3O4 electrode via selective electrodeposition of metal ions in hydrogel for enhanced electrocatalytic activity in metal-air batteries

Highlights: • Metal ions-containing agarose gel is prepared through a simple gelation process. • Agarose gel acts as a metal-ion reservoir and an ion-transport channel. • Sectionalized electrodes are easily fabricated by agarose gel-mediated electrodeposition. • Sectionalized electrodes exhibit enhanced electrocatalytic activity for both OER and ORR. • Sectionalized electrodes show excellent cyclability and stability in Zn-air batteries. Tailored designing of highly active electrocatalysts plays a key role in determining the overall electrochemical performance of metal-air batteries for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). We report herein a facile agarose gel-mediated strategy for the selective electrodeposition of MnO₂ and Co₃O₄ onto 3D porous nickel foam, in an attempt to produce a sectionalized MnO₂-Co₃O₄ electrode with low physical interference on catalytic function. The as-prepared agarose hydrogel with metal precursor ions allows the electrochemical deposition only onto the contact area between the gel and the substrate. The resulting electrodes are completely sectionalized by two different catalyst (MnO₂ and Co₃O₄) coating layers within the 3D porous nickel foam. This novel structure enhances both the ORR/OER catalytic activities compared to those of bare metal oxide catalyst electrodes and even after 400 h of operation (equivalent to ~100 cycles), the sectionalized MnO₂-Co₃O₄ electrode shows excellent cycling performance and long-term stability in rechargeable Zn-air batteries. As such, this novel sectionalized electrode configuration has potential for wide applications in the fabrication of other electrode structures employing various metal oxides.