Aluminum-air battery is a promising candidate for large-scale energy applications because of its low cost and high energy density. Remarkably, tremendous efforts have been concentrated on developing efficient and stable cathode electrocatalysts toward the oxygen reduction reaction. In this work, a hydrothermal-calcination approach was utilized to prepare novel reduced graphene oxide (rGO)-supported hollow ZnO/ZnCoO nanoparticle-embedded carbon nanocages (ZnO/ZnCoO/C@rGO) using a zeolitic imidazolate framework (ZIF-67)/graphene oxide/zinc nitrate composite as the precursor. The ZnO/ZnCoO/C@rGO hybrid exhibits remarkable electrocatalytic performance for oxygen reduction reaction under alkaline conditions and superior stability and methanol tolerance to those of the commercial Pt/C catalyst. Furthermore, novel and simple Al-air coin cells were first fabricated using the hybrid materials as cathode catalysts under ambient air conditions to further investigate their catalytic performance. The coin cell with the ZnO/ZnCoO/C@rGO cathode catalyst displays a higher open circuit voltage and discharge voltage and more sluggish potential drop than those of the cell with the ZnO/ZnCoO/C cathode catalyst, which confirms that rGO can enhance the electrocatalytic activity and stability of the catalyst system. The excellent electrocatalytic performance of the ZnO/ZnCoO/C@rGO hybrid is attributed to the prominent conductivity and high specific surface area resulting from rGO, the more accessible catalytic active sites induced by the unique porous hollow nanocage structure, and synergic covalent coupling between rGO sheets and ZnO/ZnCoO/C nanocages.
Developing highly cost-effective catalysts for an oxygen reduction reaction (ORR) in fuel cells is highly significant but still full of challenges. In this work, cobalt-and nitrogen-coembedded threedimensional (3D) trumpet flower-like porous carbons (CoNC) have been prepared by a simple two-step self-assembly technique, using carbon quantum dots (CQDs) as the carbon precursor and a supermolecular gel of self-assembled melamine and Co 2+ ions as the nitrogen and cobalt sources. The resultant CoNC catalysts possess unique 3D trumpet flowerlike structures, efficient charge transfer ability, and abundant Co−N x active sites. As a catalyst for ORR, the optimized CoNC-800 (pyrolyzed at 800 °C) exhibits efficient electrocatalytic activities, longer-term stability, and strong endurance to methanol both in acidic and alkaline media. It can be worked as a prospective substitute for a commercial Pt/C catalyst for ORR in the widespread implementation of fuel cells.
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