Advanced Zinc–Air Batteries with Free-Standing Hierarchical Nanostructures of the Air Cathode for Portable Applications

Abstract

It is today advanced that the development of a free-standing (binderless) air cathode via direct growth of nonprecious metal electrocatalysts onto the surface of the conductive collector would be a cutting-edge strategy to reduce the interfacial resistance, improve the mechanical stability, and reduce the final weight and the cost of manufacturing. Here, for Zn–air batteries (ZABs), we propose an innovative binderless noble-metal-free hierarchical nanostructured bifunctional air cathode in which high-density MnO x nanorods (NRs) are directly grown on carbon nanotubes (CNTs) themselves synthesized on a microfibrous carbon paper (CP) substrate. All carbon/MnO x air cathodes achieved specific capacities very close to the theoretical value of 820 mAh gZn –1. A very stable voltage gap between the charge and discharge processes along hundred cycles was obtained, demonstrating the stability and good bifunctional electrocatalytic activities of these cathodes toward the oxygen reduction reaction/oxygen evolution reaction in a real ZAB device. As a proof-of-concept for handheld electronic applications, a ZAB assembled with CP/MnO x NRs as the air electrode and a Zn plate anode operated a timer for 14 days successfully, whereas two ZAB-based CNTs/MnO x cathodes connected in series powered a 2 V light-emitting diode (LED) bulb and a 3 V multimeter. The proposed strategy and results may pave the way for the rational design of hierarchical free-standing bifunctional electrocatalysts for ZABs, other metal–air batteries, and fuel cells.

Hybrid Carbon Sphere Chain–MnO2 Nanorods as Bifunctional Oxygen Electrocatalysts for Rechargeable Zinc–Air Batteries

“…Further performances of CSCs and CSC-MnO x nanorods as air cathodes were examined in a homemade ZAB. 15 , respectively, values that are close to 820 mAh g Zn −1 (theoretical value). 58 These results validate the good performance of the ZAB owing to the very good ORR/ OER electrocatalytic activities of the CSC/MnO x nanorodbased hybrid materials.…”

“…The CVs in the O 2 -saturated electrolyte show ORR waves at around 0.81, 0.82, and 0.78 V, respectively at the CSCs/MnO x , Func CSCs-0.2M/MnO x , and Func CSCs-2M/MnO x (Figure a). The LSV curves at the RRDE (Figure b) reveal that J L of CSC-based MnO x is remarkably much higher than those of pristine CSCs or Func CSC counterparts (Figure b) or CP/MnO x . The electron transfer number and the intermediate peroxide percentage results are shown in Figure c,d.…”

“…Details regarding hydrothermal synthesis can be found elsewhere . Briefly, 0.266 g (1.67 mmol) of KMnO 4 (99% purity, Sigma-Aldrich) was dissolved in 18.75 mL of distilled water (Millipore Milli-Q, 18.2 MΩ·cm of resistivity) with the injection of 0.42 mL of HCl (37% purity, Sigma-Aldrich).…”

“…However, MnO x ’s poor durability and low electrical conductivity prohibit its wide application in oxygen electrocatalysis. To remedy these problems, often MnO x has been associated with Co or Ni and/or carbon nanostructures such as carbon nanotubes (CNTs) or graphene. ,− Still, MnO x species, not possessing sufficient OER active sites, hamper its utilization as a bifunctional catalyst.…”

“…Details regarding hydrothermal synthesis can be found elsewhere. 15 Briefly, 0.266 g (1.67 mmol) of KMnO 4 (99% purity, Sigma-Aldrich) was dissolved in 18.75 mL of distilled water (Millipore Milli-Q, 18.2 MΩ•cm of resistivity) with the injection of 0.42 mL of HCl (37% purity, Sigma-Aldrich). CSC samples were then immersed in the abovementioned solution and the whole arrangement was placed in a 25 mL autoclave (Teflon-lined stainless steel).…”