Double-Faced Atomic-Level Engineering of Hollow Carbon Nanofibers as Free-Standing Bifunctional Oxygen Electrocatalysts for Flexible Zn–Air Battery

Abstract

Flexible solid-state zinc–air batteries (ZABs) with low cost, excellent safety, and high energy density has been considered as one of ideal power sources for portable and wearable electronic devices, while their practical applications are still hindered by the kinetically sluggish cathodic oxygen reduction and oxygen evolution reactions (ORR/OER). Herein, a Janus-structured flexible free-standing bifunctional oxygen electrocatalyst, with OER-active O, N co-coordinated Ni single atoms and ORR-active Co3O4@Co1–x S nanosheet arrays being separately integrated at the inner and outer walls of flexible hollow carbon nanofibers (Ni-SAs/HCNFs/Co-NAs), is reported. Benefiting from the sophisticated topological structure and atomic-level-designed chemical compositions, Ni-SAs/HCNFs/Co-NAs exhibits outstanding bifunctional catalytic activity with the ΔE index of 0.65 V, representing the current state-of-the-art flexible free-standing bifunctional ORR/OER electrocatalyst. Impressively, the Ni-SAs/HCNFs/Co-NAs-based liquid ZAB show a high open-circuit potential (1.45 V), high capacity (808 mAh g–1 Zn), and extremely long life (over 200 h at 10 mA cm–2), and the assembled flexible all-solid-state ZABs have excellent cycle stability (over 80 h). This work provides an efficient strategy for developing high-performance bifunctional ORR/OER electrocatalysts for commercial applications.

[2,1,3]-Benzothiadiazole-Spaced Co-Porphyrin-Based Covalent Organic Frameworks for O2 Reduction

“…Prolonged reaction times were needed for Co@rhm-PorBTD (7 days) while Co@ sql-PorBTD crystallization occurred within 3 days (Figures S4 and S5). Co@rhm-PorBTD possesses a tessellated structure due to the use of the vertex elongated linker (BTD [4]), while Co@sql-PorBTD possesses a square lattice due to the polycondensation between the porphyrin-based square neutral structure and the linear BTD [2] linker. Fourier transform infrared spectra (Figure S6) showed peaks located at 1599 and 1602 cm −1 for Co@sql-PorBTD and Co@ rhm-PorBTD, respectively, which are characteristic of the C� N stretching band along with a decrease of the C�O (1690 cm −1 ) stretching band of BTD [2] and BTD [4].…”

“…87 Single-Molecule Calculations. The geometries and electronic structures of COF subunits BTD [2], BTD [4], and Co@Por(NH 2 ) 4 were calculated at the density functional theory (DFT) level using the long-range corrected ωB97X-D functional 88 as implemented in the Gaussian 09 package. 89 The SDD basis set and corresponding effective core potential 90 were used for cobalt, and an all-electron 6-31G(d,p) 91,92 basis set was used for the other atoms.…”

“…Figure 1. Structures of BTD[4], Co@Por(NH 2 ) 4 , and BTD[2] with electrostatic potential (ESP) maps and computed value of ionization potentials (IP) and electron affinities (EA) for BTD[4], Co@Por(NH 2 ) 4 , and BTD[2]. (b) Scheme of the synthesis of Co@rhm-PorBTD (left side) and Co@sql-PorBTD (right side) through[4 + 4] and[4 + 2] imine polycondensation, respectively.…”

Interfacial Engineering of Leaf-like Bimetallic MOF-Based Co@NC Nanoarrays Coupled with Ultrathin CoFe-LDH Nanosheets for Rechargeable and Flexible Zn-Air Batteries

“…With the rapid growth of energy demand and the ever-worsening of environmental issues, it is extremely important to explore new energy storage and conversion devices that are economical, efficient, and eco-friendly [ 1 , 2 , 3 , 4 ]. Concurrently, electronics are developing towards portability and flexibility in recent years, posing a major challenge to flexible wearable energy storage devices [ 5 , 6 , 7 ]. As one of the next-generation alternative energy technologies, rechargeable Zn-air batteries (ZABs) have broad application prospects in future electric vehicles, portable electronic products, flexible wearable electronic devices, and off-grid power supplies due to their large theoretical energy density, high safety, abundant resources, and environmental amity [ 6 , 8 , 9 ].…”

Quasi-Solid-State Flexible Zn–Air Batteries with a Hydrophilic-Treated Co@NCNTs Array Electrocatalyst and PEO–PANa Electrolyte

“…In recent years, transition metal–nitrogen–carbon (TM–N–C) materials have been widely reported in OER and ORR, and they have been considered as the most promising cathode materials for ZABs. , Generally, the ORR electrocatalytic activities of transition metals in alkaline media are in the order Fe > Co > Ni, while their OER electrocatalytic performances are in the order Ni > Co > Fe. − It is evident that Co–N–C materials are highly promising bifunctional catalysts, also thanks to their moderate adsorption-resolution free energy for both ORR and OER intermediates. , …”