Nature of Carbon Materials Used as Nondoped Electrodes for Oxygen Reduction Reaction and Supercapacitor Applications

Understanding the nature of electrode materials used in clean energy conversion systems is very important for promoting the comercialization of these systems. Herein, we investigate the essential characteristics of nondoped electrodes for oxygen reduction reaction (ORR) and supercapacitor applications based on three typical types of carbon materials, namely, carbon nanotubes (CNTs, one-dimensional), graphene (G, two-dimensional) and carbon black (BP2000, three-dimensional) by using the corroborated physical characterizations and electrochemical measurements. Several insights are obtained from the relationship between the microstructure and electrochemical performance: (1) the ORR electrocatalytic activity is mainly related to the O content rather than to the specific surface area and the defect degree; (2) G has the largest specific capacitance, most likely due to a better electrical conductivity and its unique two-dimensional microstructure rather than its O content, specific surface area and defect degree. This work confirms that different types of carbon materials are suitable for different applications: CNTs are advantageous for the ORR applications, while G is a promising electrode material for supercapacitor applications.