3D Spatial Combination of CN Vacancy‐Mediated NiFe‐PBA with N‐Doped Carbon Nanofibers Network Toward Free‐Standing Bifunctional Electrode for Zn–Air Batteries

Abstract

Constructing flexible free‐standing electrodes with efficient bifunctional performance is significant for improving the performance of flexible Zinc–air batteries. Herein, a flexible free‐standing bifunctional electrode (N2‐NiFe‐PBA/NCF/CC‐60) is constructed by the 3D spatial combination of CN vacancy‐mediated NiFe Prussian Blue Analogue (NiFe‐PBA) and N‐doped carbon nanofibers (NCF) rooted on carbon cloth (CC). The in situ formed CN vacancies by N2‐plasma activation tune the local coordination environment and electronic structure of Ni‐Fe active sites in NiFe‐PBA, thus improving the oxygen evolution reaction (OER) catalytic intrinsic activity, and restraining the loss of Fe element during OER process. The combination of NiFe‐PBA and NCF presents a 3D interworking network structure, which exhibits a large specific surface and excellent electrical conductivity, thus guaranteeing sufficient, stable, and efficient oxygen reduction reaction (ORR)/OER active sites. Therefore, the N2‐NiFe‐PBA/NCF/CC‐60 electrode delivers high‐efficiency OER activity with a low overpotential (270 mV at 50 mA cm−2) and excellent ORR performance with a positive potential of 0.89 V at 5 mA cm−2. The N2‐NiFe‐PBA/NCF/CC‐60 based Zn–air batteries display outstanding discharge/charge stability for 2000 cycles. Meanwhile, the corresponding flexible Zn–air batteries with satisfactory mechanical properties exhibit a low voltage gap of 0.52 V at 1.0 mA cm−2.

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

“…This work demonstrates superb ZABs performances in terms of power density, specific capacity, energy density, and cycle life with the ability to withstand harsh operation (Fig. 9 f and Table S7) [ 1 – 5 , 7 – 49 , 55 ]. Upon mechanical bendings from 0° to 180° and vice versa, the solid-state ZABs possess stable charge–discharge operations and galvanostatic cycling over a wide range of current densities (Figs.…”

“…As a reversible O 2 bifunctional catalysts, PEMAC@NDCN reveals the lowest overall overpotential (Δ E = E j =10 − E 1/2 ) of 0.61 V, which outperforms the reference Pt/C + RuO 2 and most reported champion bifunctional materials (Figs. 6 c, d, and Table S4), illustrating the promising free-standing cathodes for ZABs under harsh operational conditions [ 1 – 5 , 7 – 29 , 35 – 49 ].

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“…The global increment of electrical transportation and wearable/portable electronics technology urgently demands high-energy flexible rechargeable batteries that are safe and operate over wide temperatures and harsh conditions [ 1 – 5 ]. 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 ].…”

“…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.…”

“…The nanostructured supramolecular polymers have attracted significant attention as new emerging energy materials owing to the merits of large surface area, ease of functionalization, high compositional tunability, and facile synthesis process. The structural uncertainty, poor crystallinity, inferior electrical conductivity for electron transport, interfacial features to accommodate large deformation, and poor temperature tolerance of supramolecular polymers are the critical issues for the fabrication of competent oxygen bifunctional catalysts with capability for extremely harsh mechanical, environmental, and electrochemical operations [ 4 , 5 , 10 ]. These demerits of supramolecular polymers can be diminished by cross-linking of deicing mediators such as metal-free or metallic frameworks into the polymers.…”