Tianjin Key Laboratory of Composite and Functional Materials, School of Materials Science and Engineering, and ‡Key Laboratory of Advanced Ceramics and Machining Technology (Ministry of Education), Tianjin University , Tianjin 300072, China.
ACS Appl Mater Interfaces. 2017 Jul 12;9(27):22694-22703. doi: 10.1021/acsami.7b05395. Epub 2017 Jun 28.
Cobalt-based nanomaterials have been widely studied as catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) due to their remarkable bifunctional catalytic activity, low cost, and easy availability. However, controversial results concerning OER/ORR performance exist between different types of cobalt-based catalysts, especially for Co(OH) and CoO. To address this issue, we develop a facile electrochemical deposition method to grow Co(OH) directly on the skeleton of carbon cloth, and further CoO was obtained by post thermal treatment. The entire synthesis strategy removes the use of any binders and also avoids the additional preparation process (e.g., transfer and slurry coating) of final electrodes. This leads to a true comparison of the ORR/OER catalytic performance between Co(OH) and CoO, eliminating uncertainties arising from the electrode preparation procedures. The surface morphologies, microstructures, and electrochemical behaviors of prepared Co(OH) and CoO catalysts were systemically investigated by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and electrochemical characterization methods. The results revealed that the electrochemically deposited Co(OH) was in the form of vertically aligned nanosheets with average thickness of about 4.5 nm. After the thermal treatment in an air atmosphere, Co(OH) nanosheets were converted into mesoporous CoO nanosheets with remarkably increased electrochemical active surface area (ECSA). Although the ORR/OER activity normalized by the geometric surface area of mesoporous CoO nanosheets is higher than that of Co(OH) nanosheets, the performance normalized by the ECSA of the former is lower than that of the latter. Considering the superior apparent overall activity and durability, the CoO catalyst has been further evaluated by integrating it into a Zn-air battery prototype. The CoO nanosheets in situ supported on carbon cloth cathode enable the assembled Zn-air cells with large peak power density of 106.6 mW cm, low charge and discharge overpotentials (0.67 V), high discharge rate capability (1.18 V at 20 mA cm), and long cycling stability (400 cycles), which are comparable or even superior to the mixture of state-of-the-art Pt/C and RuO cathode.
基于钴的纳米材料由于其显著的双功能催化活性、低成本和易得性而被广泛研究作为氧还原反应 (ORR) 和氧析出反应 (OER) 的催化剂。然而，不同类型的钴基催化剂的 OER/ORR 性能存在争议结果，特别是对于 Co(OH) 和 CoO。为了解决这个问题，我们开发了一种简便的电化学沉积方法，直接在碳布骨架上生长 Co(OH)，并通过后热处理进一步获得 CoO。整个合成策略消除了对任何粘结剂的使用，也避免了最终电极的额外制备过程（例如，转移和浆料涂覆）。这导致了 Co(OH) 和 CoO 的 ORR/OER 催化性能的真正比较，消除了电极制备过程中出现的不确定性。通过扫描电子显微镜、透射电子显微镜、原子力显微镜和电化学表征方法系统地研究了制备的 Co(OH) 和 CoO 催化剂的表面形貌、微观结构和电化学行为。结果表明，电化学沉积的 Co(OH) 是以平均厚度约为 4.5nm 的垂直排列纳米片的形式存在。在空气气氛中进行热处理后，Co(OH) 纳米片转化为具有显著增加的电化学活性表面积 (ECSA) 的介孔 CoO 纳米片。尽管通过介孔 CoO 纳米片的几何表面积归一化的 ORR/OER 活性高于 Co(OH) 纳米片，但通过前者的 ECSA 归一化的性能低于后者。考虑到优越的表观整体活性和耐久性，将 CoO 催化剂进一步集成到锌-空气电池原型中进行评估。原位支撑在碳布阴极上的 CoO 纳米片使组装的锌-空气电池具有较大的峰值功率密度 106.6mWcm，低充放电过电位 (0.67V)，高放电速率能力 (1.18V 在 20mAcm) 和长循环稳定性 (400 次循环)，可与最先进的 Pt/C 和 RuO 阴极相媲美，甚至更好。
