Cobalt-Based Nanoparticles Decorating Carbon Nanofibers Films As Highly Efficient Electrocatalysts for Oxygen Reduction

Abstract

With increasing concerns about environment problems and sustainable energy supply systems, intensive researches have been conducted on alternative electrochemical energy storage and conversion systems with green, high efficiency and low cost [1, 2]. Specially, fuel cells and metal-air batteries have received much attention as the alternative energy systems. However, the sluggish kinetics of the oxygen reduction reaction (ORR) on the cathode side is the crucial obstacle for commercialization of the devices. Pt and its alloys are widely known for best ORR catalyst, but they have some disadvantages including poor durability, high cost and detrimental environmental effects [3]. Therefore, it is necessary to explore efficient and low-cost electrocatalysts for replacing Pt-based catalyst. For decades, much effort has been devoted to developing better and cheaper ORR electrocatalysts. Cobalt-based nanoparticles (NPs) decorated carbon materials were intensively reported due to their outstanding catalytic performances. Also, hybrid materials composed of Co-based NPs and nitrogen-doped carbon exhibit more enhanced catalytic activities due to synergistic effect [4]. Herein, we synthesized Co-based NPs decorated nitrogen-doped carbon nanofiber (CNFs) films based on electrospun polyacrylonitrile (PAN) nanofibers and evaluated their electrocatalytic activities. CNFs have been widely used in electrochemical energy storage devices because of their outstanding properties including excellent conductivity, extremely large surface areas and structural stability. In this report, CNFs play multi-functional roles as an active electrode materials, conductivity additives and substrates for supporting catalysts materials. The various samples were prepared under different temperature and gas conditions. For observing the morphologies, we carried out scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray diffraction (XRD) was also conducted to study the crystallographic structure of the decorated Co-based NPs. And we investigated chemical composition and bonding configuration of the samples by X-ray photoelectron spectroscopy (XPS). The results of XPS analysis demonstrate the synergistic effect between Co-based NPs and doped nitrogen into the CNFs. Catalytic activities were characterized by three-electrode system. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were measured for investigating the electrocatalytic activity. The results of electrochemical tests reveal that Co-based NPs decorated CNFs films show good catalytic activities toward ORR and favor four-electron transfer process. [1] M. Winter, R.J. Brodd, What are batteries, fuel cells, and supercapacitors?, Chem. Rev., 104 (2004) 4245-4270 [2] Y. Liang, Y. Li, H. Wang, J. Zhou, J. Wang, T. Regier, H. Dai, Co3O4 nanocrystals on graphene as a synergistic catalyst for oxygen reduction reaction, Nat. Mater., 10 (2011) 780-786 [3] C. Sealy, The problem with platinum, Mater. Today, 11 (2008) 65-68 [4] Y. Su, Y. Zhu, H. Jiang, J. Shen, X. Yang, W. Zou, J. Chen, C. Li, Cobalt nanoparticles embedded in N-doped carbon as an efficient bifunctional electrocatalyst for oxygen reduction and evolution reactions, Nanoscale, 6 (2014) 15080-15089 Acknowledgement "This research was supported by the MSIP(Ministry of Science, ICT and Future Planning), Korea, under the “IT Consilience Creative Program” (IITP-2015-R0346-15-1008) supervised by the IITP(Institute for Information & Communications Technology Promotion)