In Situ Coupling of Strung Co₄N and Intertwined N–C Fibers toward Free-Standing Bifunctional Cathode for Robust, Efficient, and Flexible Zn–Air Batteries

Abstract

Flexible power sources with high energy density are crucial for the realization of next-generation flexible electronics. Theoretically, rechargeable flexible zinc-air (Zn-air) batteries could provide high specific energy, while their large-scale applications are still greatly hindered by high cost and resources scarcity of noble-metal-based oxygen evolution reaction (OER)/oxygen reduction reaction (ORR) electrocatalysts as well as inferior mechanical properties of the air cathode. Combining metallic Co4N with superior OER activity and Co-N-C with perfect ORR activity on a free-standing and flexible electrode could be a good step for flexible Zn-air batteries, while lots of difficulties need to be overcome. Herein, as a proof-of-concept experiment, we first propose a strategy for in situ coupling of strung Co4N and intertwined N-C fibers, by pyrolyzation of the novel pearl-like ZIF-67/polypyrrole nanofibers network rooted on carbon cloth. Originating from the synergistic effect of Co4N and Co-N-C and the stable 3D interconnected conductive network structure, the obtained free-standing and highly flexible bifunctional oxygen electrode exhibits excellent electrocatalytic activity and stability for both OER and ORR in terms of low overpotential (310 mV at 10 mA cm(-2)) for OER, a positive half-wave potential (0.8 V) for ORR, and a stable current density retention for at least 20 h, and especially, the obtained Zn-air batteries exhibit a low discharge-charge voltage gap (1.09 V at 50 mA cm(-2)) and long cycle life (up to 408 cycles). Furthermore, the perfect bendable and twistable and rechargeable properties of the flexible Zn-air battery particularly make it a potentially power portable and wearable electronic device.

Sequentially Electrodeposited MnOX/Co-Fe as Bifunctional Electrocatalysts for Rechargeable Zinc-Air Batteries

“…The addition of Ni(OH) 2 into MnOx by reducing an amorphous MnO 2 /C suspension, in the presence of Ni 2+ with NaBH 4 , has also been reported to stabilize the morphology and phase of the active material. 51 ORR activity was improved due to the higher MnOOH content after adding the reducing agent NaBH 4 . 52 An increasing level of Mn 3+ may be expected to decrease the conductivity of MnOx; however, EIS results demonstrate that the electrical properties of MnOx/Co-Fe are enhanced by the Co-Fe coating, as will be shown later.…”

“…Sodium dodecyl sulfate (surfactant), L-ascorbic acid (antioxidant) and boric acid (buffering agent) were added to the baths to enhance the uniformity of the coating and its adhesion to the substrate. MnO X was anodically electrodeposited onto GDL at a constant current of 40 mA for 10 min in an electrolyte containing MnSO 4 . For sequentially deposited MnOx/Co-Fe, a layer of MnOx was anodically deposited first, followed by a layer of cathodically deposited Co-Fe.…”

“…3 Also, catalyst stability is a problem, because the catalyst can detach from the current collector or pulverize during battery cycling. 4 Currently, some precious metals such as Pt, Ru and Ir are recognized as the most active ORR or OER electrocatalysts. 5,6 However, their application in zinc-air batteries is limited by their high cost and low abundance.…”

Graphene-templated synthesis of sandwich-like porous carbon nanosheets for efficient oxygen reduction reaction in both alkaline and acidic media

“…Although Pt-based precious metal catalysts possess the most intriguing catalytic performance in prototype devices, the high cost associated with poor durability is a severe issue preventing their further development [11,12]. Therefore, it is urgent to develop alternative non-precious metal catalysts (NPMCs) with high electrocatalytic activity and long-term stability to promote the commercialization of metal-air batteries and fuel cells in the near future [13][14][15][16][17][18][19].…”

Enhancement of Oxygen Transfer by Design Nickel Foam Electrode for Zinc−Air Battery

“…This performance was derived from the intimate interfacial contact between the P-g-C 3 N 4 and carbon fiber paper, which facilitated the electron transfer between the two components. Despite the efforts made in the development of integrative oxygen electrodes, 35,[37][38][39][40][41][42][43][44][45][46][47][48] most of these studies have focused on the exploitation of new catalysts, whereas efforts to investigate the mass-transfer structure of the porous electrode are currently lacking. Oxygen reduction is a typical triphase reaction process, involving oxygen from the gas phase, hydroxide from the aqueous solution, and electron conduction in the solid, with charge transfer occurring at the triphase interfaces (liquid-gas-solid interfaces).…”