The rechargeable Zn−air batteries as an environmentally friendly sustainable energy technology have been extensively studied. However, it is still a challenge to develop non-noble metal bifunctional catalysts with high oxygen reduction as well as oxygen evolution reaction (ORR and OER) activity and superior durability, which limit the large-scale application of rechargeable Zn−air batteries. Herein, we synthesized an ultrastable FeCo bifunctional oxygen electrocatalyst on Se-doped CNTs (FeCo/Se-CNT) via a gravity guided chemical vapor deposition (CVD) strategy. The catalyst exhibits excellent ORR (E 1/2 = 0.9 V) and OER (overpotential at 10 mA cm −2 = 340 mV) properties simultaneously, surpassing commercial Pt/C and RuO 2 /C catalysts. More importantly, the catalyst shows an unordinary stability, that is, is no obvious decrease after 30K cycles accelerated durability test for ORR and OER processes. The small potential gap (0.75 V) represents superior bifunctional ORR and OER activities of the FeCo/ Se-CNT catalyst. The FeCo/Se-CNT catalyst possesses outstanding electrochemical performance for the rechargeable liquid and flexible all-solid-state Zn−air batteries, for example, a high open circuit voltage (OCV) and peak power density of 1.543 and 1.405 V and 173.4 and 37.5 mW cm −2 , respectively.

exhaust to generate electricity, giving new possibilities for reducing CO 2 emissions and relieving global warming. In addition, there is a lot of N 2 in the air, and nitrogen fixation can transform free N 2 into nitrogen-containing compounds that human needs. The traditional Haber-Bosch nitrogen-fixing process consumes lots of fossil fuels, leading to environmental pollution. [14,15] The metal-N 2 batteries not only use N 2 as the reactive gas, but also give a new way to synthesize the nitrogen-containing compounds and replace the Haber-Bosch nitrogen-fixing process. [16] However, metal-gas batteries face great challenges in their practical application. The sluggish electrode reaction oxygen reduction and evolution reaction (ORR and OER) in rechargeable metal-O 2 batteries resulted in low round-trip efficiency and unacceptably large overvoltage. [38][39][40][41][42] In the case of rechargeable metal-CO 2 batteries, the high overpotential of carbon oxide reduction and evolution reaction (CO 2 RR and CO 2 ER) reactions will lead to electrolyte decomposition, short cycle life, and other problems. [43,44] Besides, highly selective catalysts for nitrogen reduction reaction (NRR) are also required for metal-N 2 batteries to avoid paralleled hydrogen evolution reaction (HER) and improve cell efficiency. [45,46] Therefore, in order to solve the above key problems and improve the cycling efficiency of metal-gas batteries, it is necessary to develop appropriate electrocatalysts.Carbon-based non-noble metal catalysts leap out among many catalysts due to their high surface area, suitable size, and rich variety. [47,48] Carbon-based non-noble metal catalysts usually have carbon nanotube, graphene, or other carbon materials as primary structures with transition metal active sites. [49] In contrast with precious metal catalysts, carbon-based nonprecious metal catalysts have lower cost and better toxicity resistance, and the gap in activity can be made up by increasing the amount of the catalyst loading. [50] In addition, the presence of coordinating atoms (such as N, O, S, and P) benefits the catalytic activities of catalysts. A number of articles have appeared in recent years describing the development of carbon-based non-noble metal catalysts, but reviews relating to the metal-gas batteries with these catalysts are rare. Recently, researches on metal-gas batteries with carbon-based non-precious metal catalysts were reported in large amounts, Figure 1c. This review focuses on the recent studies on carbon-based non-noble metal Metal-gas batteries draw a lot of attention due to their superiorities in high energy density and stable performance. However, the sluggish electrochemical reactions and associated side reactions in metal-gas batteries require suitable catalysts, which possess high catalytic activity and selectivity. Although precious metal catalysts show a higher catalytic activity, high cost of the precious metal catalysts hinders their commercial applications. In contrast, nonprecious metal catalysts complement the we...

Abstract. In order to solve the inconvenience of searching the location of classroom, we developed an offline classroom searching application based on smart mobile phone, which makes it possible to achieve the searching function in five campuses. This paper attaches importance to the installation of classroom data, the transition of different searching pages, the optimization of searching efficiency and data updating. This system doesn't need to connect to the Internet and impropriates few memory spaces. Moreover, the speed of searching is very fast. Therefore, it's a great tool that provides teachers and students with conveniences.