Atomic Fe–N₄/C in Flexible Carbon Fiber Membrane as Binder‐Free Air Cathode for Zn–Air Batteries with Stable Cycling over 1000 h

Abstract

competitive in comparison with other energy storage/conversion systems, such as fuel cells or lithium/sodium-ion batteries. [2] A typical ZAB stores and releases energy mainly through the redox reaction between the Zn anode and air cathode. The major challenge for air cathode is the large overpotentials due to the sluggish kinetics of oxygen reduction and evolution reactions (ORR/OER) during charging/ discharging processes. [3] To date, despite the satisfactory catalytic performance by state-of-the-art Pt-based and Ir/Ru-based catalysts, scalable and sustainable deployment of ZABs is severely impeded by the poor economic viability and low durability of these scarce precious metals. [4] Recently, single-atom catalysts (SACs) with M-N x /C moieties (M = Fe, Co, Ni, Mn) have attracted increasing attention as ORR and/or OER electrocatalysts due to their maximum atomic utilization, high intrinsic activity, and low cost. [5] Among the coordination structures, four pyridinic N-coordinated iron moiety in carbon matrix (Fe-N 4 /C) is one of the most potential catalytic sites for ORR since its more stable structure than other nitrogen coordination numbers and higher intrinsic activity than other central metal atoms. [6] Besides, the long-range interactions of other heteroatoms (such as S and P) from carbon supports are capable of tailoring local electronic structure of the Fe-N 4 /C moieties and carbon matrix, thereby promoting the adsorption and conversion of the ORR and/or OER intermediates at preferable reaction barriers. [7] Noble-metal-free, durable, and high-efficiency electrocatalysts for oxygen reduction and evolution reaction (ORR/OER) are vital for rechargeable Zn-air batteries (ZABs). Herein, a flexible and free-standing carbon fiber membrane immobilized with atomically dispersed Fe-N 4 /C catalysts (Fe/SNCFs-NH 3 ) is synthesized and used as air cathode for ZABs. The intertwined fibers with hierarchical nanopores facilitate the gas transportation, electrolyte infiltration and electron transfer. The large specific surface area exposes a high concentration of Fe-N 4 /C sites embedded in the carbon matrix. Modulation of local atomic configurations by sulfur doping in Fe/SNCFs-NH 3 catalyst leads to excellent ORR and enhanced OER activities. The as-synthesized Fe/ SNCFs-NH 3 catalyst demonstrates a positive half-wave potential of 0.89 V and a small Tafel slope of 70.82 mV dec -1 , outperforming the commercial Pt/C (0.86 V/94.74 mV dec -1 ) and most reported M-N x /C (M = Fe, Co, Ni) catalysts. Experimental characterizations and theoretical calculations uncover the crucial role of S doping in regulating ORR and OER activities. The liquid-state ZABs with Fe/SNCFs-NH 3 catalyst as air cathode deliver a large peak power density of 255.84 mW cm -2 and long-term cycle durability over 1000 h. Solidstate ZAB shows stable cycling at various flat/bent/flat states, demonstrating great prospects in flexible electronic device applications.The ORCID identification number(s) for the author(s) of this article can be found un...

Supramolecular Polymer Intertwined Free-Standing Bifunctional Membrane Catalysts for All-Temperature Flexible Zn–Air Batteries

“…N 1 s spectra (Figs. 3 e, S3, and Table S2) demonstrates the five characteristics core-states of pyridinic N (398.8 eV), pyrrolic N (399.6 eV), graphitic N (400.4 eV), quaternary N (401.6 eV), and oxidized N (402.6 eV) [ 7 , 16 , 26 , 27 , 41 , 42 ]. The pyridinic N transforms the local electronic structure of adjacent carbon (positively charged) stimulating the construction of operational active sites and graphitic N enables the four-electron transfer oxygen reaction kinetics.…”

“…Commercial Li-ion battery operations are strongly restricted to the temperature range of − 20 to + 15 °C with severe reduction in energy and power densities [ 6 ]. Among the aqueous/non-aqueous metal–air batteries (alkali metals: Li, Na, and K), alkaline earth metals (Mg) and transition or post-transition metals (Fe, Zn, Al, Sn), Zn–air batteries (ZABs) with earth-abundant Zn resources, high theoretical energy density (1086 Wh kg −1 ), cost-effectiveness, and intrinsic safety are the most competitive energy storage systems to satisfy the growing practical requirements [ 7 – 10 ].…”

“…Recently, most reported electrodes are integrated with polymer binders and then dispersed on the conductive substrates. The loading of binders will inevitably lead to the increase in oxygen transport resistance with deterioration for active surface sites, thus causing large overpotentials, reduction in ZABs capacities and long-term operations [ 5 – 7 ]. Therefore, constructing self-standing, highly efficient oxygen bifunctional membrane electrodes with intrinsic bendability is one of the alternative strategies.…”

Nanosized high entropy spinel oxide (FeCoNiCrMn)3O4 as a highly active and ultra-stable electrocatalyst for the oxygen evolution reaction

“…4–6 The anodic oxygen evolution reaction of water splitting involves a four-electron transfer process and usually causes a high overpotential and a large kinetic energy barrier, which is why it is considered to be the rate-limiting step for the entire water splitting reaction. 7,8 In order to improve the efficiency of water splitting, noble metal oxide catalysts (RuO 2 , IrO 2 ) are often adopted, but the high price, low resource abundance and poor stability of noble metal oxides restrict their large-scale application in industrial production. 9–11…”

Compressible Zn–Air Batteries Based on Metal–Organic Frameworks Nanoflake‐Assembled Carbon Frameworks for Portable Motion and Temperature Monitors

“…It is worth noting that NiFe NF/NCFs-based ZAB has advantages on OCP, peak power density, and specific capacity as compared with other recently reported works, as shown in Table S1, Supporting Information, and Figure 4e. [50][51][52][53][54][55] This remarkable FZAB performance was attributed to the superior catalytic activity of NiFe NF/NCFs and enlarged contact area to gel electrolyte that was endowed by well-designed electrode-electrolyte interface. The electrode-electrolyte interfaces were further investigated by evaluating the force to separate the cathode and the gel electrolyte.…”