Iron–nitrogen–carbon materials (Fe–N–C) are known for their excellent oxygen reduction reaction (ORR) performance. Unfortunately, they generally show a laggard oxygen evolution reaction (OER) activity, which results in a lethargic charging performance in rechargeable Zn–air batteries. Here porous S‐doped Fe–N–C nanosheets are innovatively synthesized utilizing a scalable FeCl3‐encapsulated‐porphyra precursor pyrolysis strategy. The obtained electrocatalyst exhibits ultrahigh ORR activity (E1/2 = 0.84 V vs reversible hydrogen electrode) and impressive OER performance (Ej
= 10 = 1.64 V). The potential gap (ΔE = Ej
= 10 − E1/2) is 0.80 V, outperforming that of most highly active bifunctional electrocatalysts reported to date. Furthermore, the key role of S involved in the atomically dispersed Fe–Nx species on the enhanced ORR and OER activities is expounded for the first time by ultrasound‐assisted extraction of the exclusive S source (taurine) from porphyra. Moreover, the assembled rechargeable Zn–air battery comprising this bifunctional electrocatalyst exhibits higher power density (225.1 mW cm−2) and lower charging–discharging overpotential (1.00 V, 100 mA cm−2 compared to Pt/C + RuO2 catalyst). The design strategy can expand the utilization of earth‐abundant biomaterial‐derived catalysts, and the mechanism investigations of S doping on the structure–activity relationship can inspire the progress of other functional electrocatalysts.
We report a novel “sacrificial template-accelerated hydrolysis” (STAH) approach to the synthesis of iron oxide-based nanotube arrays including hematite α-Fe2O3 and magnetite Fe3O4 on centimeter-scale conducting alloy substrates. ZnO nanowire arrays are chosen as the inexpensive and sacrificial templates that do not contribute to the component of final iron oxide nanotubes but can be in situ dissolved by the acid produced from the Fe3+ precursor hydrolysis. Interestingly, the ZnO template dissolution in turn accelerates the Fe3+ hydrolysis, which is essential to initiating the nanotube formation. Such a STAH approach provides a morphology-reservation transformation, when various shaped ZnO templates are adopted. Moreover, by introducing glucose into the precursor solution, we also successfully obtain carbon/hematite(C/α-Fe2O3) composite nanotube arrays on large-area flexible alloy substrate, with a large number of pores and uniform carbon distribution at a nanoscale in the nanotube walls. These arrays have been demonstrated as excellent additive-free anode materials for lithium ion batteries in terms of good cycling performance up to 150 times (659 mA h g−1) and outstanding rate capability. Our result presents not only a new route for inorganic nanotube formation but also an insight for rational design of advanced electrode materials for electrochemical batteries and sensors.
Carbon/ZnO nanorod arrays on nickel substrate have been fabricated over a large area by the simple carbonization of preadsorbed glucose on ZnO arrays at 500 °C in argon gas. The uniform coating of average 6 nm carbon shell on ZnO nanorod surface is confirmed. The novel array architecture possesses both the electroactivity of carbon and the electrochemical advantages of array structure on conductive substrate. When used as anode for Li ion batteries, it displays significantly improved performance in terms of cycling stability and rate capability. The observed lithium storage ability ranges among the best reported to date for ZnObased anode. We believe that the novel carbon-coating route is general and can be extendable to other metal oxide nanoarray electrodes.
We report for the first time a facile and direct synthesis of large-scale cobalt monoxide (CoO) porous nanowire arrays (NWAs) with robust mechanical adhesion to flexible conductive substrate (Ti foil) by a two-step method. Significantly raw salt cubic CoO of high quality from the complete pyrolysis of cobalt-hydroxide-carbonate (precursor) is achieved. When serving as lithium-ion battery electrodes in the absence of any ancillary materials (carbon black and binder), the as-obtained well-aligned CoO NWAs, possessing both the completely reversible electrochemical properties and unique advantages originating from integrated one-dimensional (1D) nanostructured architecture, exhibit good high-rate capability at a rate of 1 C (716 mA/g), 2 C (1432 mA/g), 4 C (2864 mA/g), and 6 C (4296 mA/g), respectively.
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