Hierarchical Co3O4 Nano-Micro Arrays Featuring Superior Activity as Cathode in a Flexible and Rechargeable Zinc-Air Battery

Abstract

All-solid-state zinc-air batteries are characterized as low cost and have high energy density, providing wearable devices with an ideal power source. However, the sluggish oxygen reduction and evolution reactions in air cathodes are obstacles to its flexible and rechargeable application. Herein, a strategy called MOF-on-MOF (MOF, metal-organic framework) is presented for the structural design of air cathodes, which creatively develops an efficient oxygen catalyst comprising hierarchical Co₃O₄ nanoparticles anchored in nitrogen-doped carbon nano-micro arrays on flexible carbon cloth (Co₃O₄@N-CNMAs/CC). This hierarchical and free-standing structure design guarantees high catalyst loading on air cathodes with multiple electrocatalytic activity sites, undoubtedly boosting reaction kinetics, and energy density of an all-solid-state zinc-air battery. The integrated Co₃O₄@N-CNMAs/CC cathode in an all-solid-state zinc-air battery exhibits a high open circuit potential of 1.461 V, a high capacity of 815 mAh g^-1 Zn at 1 mA cm^-2, a high energy density of 1010 Wh kg^-1 Zn, excellent cycling stability as well as outstanding mechanical flexibility, significantly outperforming the Pt/C-based cathode. This work opens a new door for the practical applications of rechargeable zinc-air batteries in wearable electronic devices.

Keywords: Co3O4; nano‐micro arrays; cathodes; superior activities; zinc–air batteries.

Figure 1

a) Schematic illustration of the formation process of ZIF‐L‐D‐Co₃O₄/CC; b–d) SEM images and e–g) TEM images of ZIF‐L/CC, ZIF‐L‐D/CC, and ZIF‐L‐D‐Co₃O₄/CC; h,i) HRTEM and SAED images of ZIF‐D‐Co₃O₄ and j,k) ZIF‐L‐Co₃O₄.

Figure 2

a,b) SEM images and d,e) TEM images of ZIF‐D‐Co₃O₄/CC and ZIF‐L‐Co₃O₄/CC; The comparison of c) active material loading and f) double layer capacitance of ZIF‐D‐Co₃O₄/CC, ZIF‐L‐Co₃O₄/CC, and ZIF‐L‐D‐Co₃O₄/CC.

Figure 3

a) Polarization curves, b) Tafel plots, c) polarization curves before and after 10 000 potential sweeps between 1.4 and 1.6 V at 50 mV s⁻¹ for OER test; d) Polarization curves, e) Tafel plots, f) polarization curves before and after 10 000 potential sweeps between 0.8 and 1.0 V at 50 mV s⁻¹ for ORR test; g) Comparison of stability test between ZIF‐L‐D‐Co₃O₄/CC and Pt/C as the air cathode in aqueous ZABs.

Figure 4

a) Discharge and charge polarization curves, b) power–current density curves, c) voltage–capacity curves of solid‐state ZABs with air cathodes of ZIF‐L‐D‐Co₃O₄/CC and Pt/C. d) Mechanical flexibility and stability tests of the solid‐state rechargeable ZABs under continuously mechanical altering (digital images in inset) for every three cycles. e) Discharge–charge voltage profiles of ZIF‐L‐D‐Co₃O₄/CC at 1 mA cm⁻² (10 min for discharging and 10 min for charging) at the flat condition and different bending conditions.

Figure 5

a) Schematic representation of three all‐solid‐state ZABs in series. Three‐series ZABs power 75 red LEDs with “SCNU” shape in different bending angles of b) 180°, c) 135°, d) 90°, e) 45°, and f) 0°. Photograph of g) a red LED breastpiece (3 V) activated by three‐series ZABs in flat state, h) three‐series ZABs as a wearable bracelet and i) power the breastpiece. Three‐series ZABs power a red LED breastpiece (3 V) in different bending radius of j) 4, k) 3, and l) 2.5 cm.