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Abstract：
Fabricating highly efficient and robust oxygen reduction reaction (ORR) electrocatalysts is challenging but desirable for practical Zn-air batteries. As an early transition-metal oxide, zirconium dioxide (ZrO2) has emerged as an interesting catalyst owing to its unique characteristics of high stability, anti-toxicity, good catalytic activity, and small oxygen adsorption enthalpies. However, its intrinsically poor electrical conductivity makes it difficult to serve as an ORR electrocatalyst. Herein, we report ultrafine N-doped ZrO2 nanoparticles embedded in an N-doped porous carbon matrix as an ORR electrocatalyst (N-ZrO2/NC). The N-ZrO2/NC catalyst displays excellent activity and long-term durability with a half-wave potential (E1/2) of 0.84 V and a selectivity for the four-electron reduction of oxygen in 0.1 M KOH. Upon employment in a Zn-air battery, N-ZrO2/NC presented an intriguing power density of 185.9 mW cm-2 and a high specific capacity of 797.9 mA h gZn -1, exceeding those of commercial Pt/C (122.1 mW cm-2 and 782.5 mA h gZn -1). This excellent performance is mainly attributed to the ultrafine ZrO2 nanoparticles, the conductive carbon substrate, and the modified electronic band structure of ZrO2 after N-doping. Density functional theory calculations demonstrated that N-doping can reduce the band-gap of ZrO2 from 3.96 eV to 3.33 eV through the hybridization of the p state of the N atom with the 2p state of the oxygen atom; this provides enhanced electrical conductivity and results in faster electron-transfer kinetics. This work provides a new approach for the design of other enhanced semiconductor and insulator materials.
摘要：
制造高效且稳健的氧还原反应(ORR)电催化剂是具有挑战性的,但对于实际的Zn-空气电池是理想的。作为一种早期的过渡金属氧化物,二氧化锆（ZrO2）由于其独特的高稳定性特性而成为一种有趣的催化剂，抗毒性，良好的催化活性，和小的氧吸附焓。然而,其固有的差的导电性使得其难以用作ORR电催化剂。在这里，我们报告了嵌入N掺杂多孔碳基质中的超细N掺杂ZrO2纳米颗粒作为ORR电催化剂（N-ZrO2/NC）。N-ZrO2/NC催化剂表现出优异的活性和长期耐久性，其半波电位（E1/2）为0.84V，并且在0.1MKOH中对氧的四电子还原具有选择性。在锌空气电池中就业时，N-ZrO2/NC的功率密度为185.9mWcm-2，比容量为797.9mAhgZn-1，超过了商用Pt/C（122.1mWcm-2和782.5mAhgZn-1）。这种优异的性能主要归功于超细ZrO2纳米颗粒，导电碳基材，以及N掺杂后ZrO2的电子能带结构。密度泛函理论计算表明，通过N原子的p态与氧原子的2p态的杂化，N掺杂可以将ZrO2的带隙从3.96eV降低到3.33eV；这提供了增强的电导率并导致更快的电子转移动力学。这项工作为其他增强型半导体和绝缘体材料的设计提供了一种新的方法。
