Novel Co3O4 Nanoparticles/Nitrogen-Doped Carbon Composites with Extraordinary Catalytic Activity for Oxygen Evolution Reaction (OER)

Nano-Micro Lett. (2018)10:15 DOI 10.1007/s40820-017-0170-4 ARTICLE Novel Co3O4 Nanoparticles/Nitrogen-Doped Carbon Composites with Extraordinary Catalytic Activity for Oxygen Evolution Reaction (OER) Xiaobing Yang1,3 . Juan Chen2 . Yuqing Chen4 . Pingjing Feng4 . Huixian Lai4 . Jintang Li4 . Xuetao Luo4 Received: 21 August 2017 / Accepted: 8 October 2017  The Author(s) 2017. This article is an open access publication Highlights • • Co3O4 nanoparticles/nitrogen-doped carbon (Co3O4/NPC) composites were successfully fabricated from zeolitic imidazolate framework 67 (ZIF-67), and the composite structure could be well controlled by adjusting the structure of ZIF67. M-Co3O4/NPC composites derived from flower-like ZIF-67 showed the highest activities for the oxygen evolution reaction (OER). Abstract Herein, Co3O4 nanoparticles/nitrogen-doped carbon (Co3O4/NPC) composites with different structures were prepared via a facile method. Structure control was achieved by the rational morphology design of ZIF-67 precursors, which were then pyrolyzed in air to obtain Co3O4/NPC composites. When applied as catalysts for the oxygen evolution reaction (OER), the M-Co3O4/NPC composites derived from the flower-like ZIF-67 showed + Co2+ 2-Hmim Seed crystals Co3O4 M-ZIF-67 OH− 4OH− O2 + 4e− + 2H2O O2 Juan Chen and Xiaobing Yang have contributed equally to this work. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s40820-017-0170-4) contains supplementary material, which is available to authorized users. & Xuetao Luo 1 College of Ecology and Resource Engineering, Wuyi University, Wuyishan 354300, Fujian, People’s Republic of China 2 Department of Pharmacy, Zhongshan Hospital, Xiamen University, Xiamen 361004, Fujian, People’s Republic of China 3 Fujian Provincial Key Laboratory of Eco-Industrial Green Technology, Wuyi University, Wuyishan 354300, Fujian, People’s Republic of China 4 Fujian Key Laboratory of Advanced Materials, College of Materials, Xiamen University, Xiamen 361005, Fujian, People’s Republic of China M-Co3O4/NPC superior catalytic activities than those derived from the rhombic dodecahedron and hollow spherical ZIF-67. The former M-Co3O4/NPC composite displayed a small overpotential of 0.3 V, low onset potential of 1.41 V, small Tafel slope of 83 mV dec-1, and a desirable stability. (94.7% OER activity was retained after 10 h.) The excellent performance of the flower-like M-Co3O4/NPC composite in the OER was attributed to its favorable structure. Keywords Co3O4 nanoparticles  Nitrogen-doped carbon  ZIF-67  Catalytic  Oxygen evolution reaction (OER) 123 15 Page 2 of 11 1 Introduction Depletion of fossil fuels and the rapidly growing energy demands have necessitated the development of sustainable energy conversion and storage systems such as metal–air batteries, water splitting devices, and fuel cells [1–4]. The development of durable, highly efficient, low-cost, and eco-friendly electrocatalysts for the oxygen evolution reaction (OER) is crucial for the commercial application of these renewable energy technologies [5, 6]. To date, precious metal-based materials, such as RuO2 and IrO2, have been considered as the most optimal catalysts for OER owing to their lowest over-potentials at practical current densities [7]. However, their commercial applications have been severely impeded because of their poor stability, prohibitive cost, and low selectivity [8]. Recently, significant efforts have been made to explore transition metal-based electrocatalysts for the OER because of their low cost, abundant reserves, environmental benignity, and resistance to corrosion in alkaline solutions [9–12]. Among them, Co-based catalysts have emerged as promising alternatives for precious metal-based catalysts [13–16]. The electrocatalytic activity for OER is closely related to the active sites and electronic conductivity of the catalysts. Previous research has demonstrated that active sites can be engineered by modulating the particle size, pore structure [17, 18], and the crystallinity [19, 20] of Co3O4. Furthermore, coupling with carbon effectively improves the electronic conductivity of the catalysts [21–23]. Nevertheless, carbon itself as a catalyst displays relatively low catalytic OER activity. Recent studies have shown that doping with either nitrogen or transition metals into carbon nanostructure can efficiently promote its catalytic performance [23–26]. The template method has proven to be an effective protocol for obtaining nitrogendoped Co3O4/C composites. In this method, various organic hybrids, which contain both the transition metal and nitrogen, are used as precursors such as melamine [27], porphyrin [28], polyaniline [29, 30], and salen [31]. However, it is hard to control the size, structure, and morphology of these organic hybrids in an exact manner; therefore, deficiencies and non-uniform distributions of active sites are prevalent, which are also crucial for electrocatalytic activity. Metal organic frameworks (MOFs) have attracted a significant attention as materials for the preparation of nonprecious metal electrocatalysts because of their inherent advantages such as a controllable porous structure, innate doping with heteroatoms, and an ultrahigh surface area [32, 33]. Zeolitic imidazolate frameworks (ZIFs) have proven to be promising as pyrolytic precursors for various porous metal oxides/doped carbon composites [34–36]. Via 123 Nano-Micro Lett. (2018)10:15 direct pyrolysis, carbon layers with a porous structure can be formed in situ with metal nanoparticles encapsulated homogeneously, and sufficient contacts can be formed between the metal nanoparticles and the carbon matrix. Notably, a highly ordered three-dimensional structure promotes the structural stability of MOFs against pyrolysis, and the remarkable surface-to-volume ratio of MOFs can effectively promote the electrochemical catalytic reactions. Among the variety of MOF materials available, ZIF-67 is one of the most widely investigated ones because of its high concentration of active cobalt sites as well as a facile synthetic method. Herein we have proposed a facile method to prepare Co3O4/NPC composites with different morphologies derived from ZIF-67. By slightly modulating the synthetic route of the ZIF-67 precursors, it was possible to control the morphology of the product. Thus, in addition to the typical rhombic dodecahedron morphology, novel flower-like ZIF-67 and hollow spherical ZIF-67 were fabricated. These ZIF-67 precursors were then pyrolyzed to obtain the Co3O4/NPC composites of different structures, named T-Co3O4/NPC, M-Co3O4/NPC, and H-Co3O4/NPC, respectively. The electrocatalytic activities for OER of the three composites were then investigated to determine the most favorable morphology for the highest electrocatalytic performance for the OER. 2 Experimental 2.1 Chemicals Cobalt nitrate hexahydrate (Co(NO3)26H2O, [ 99 (...truncated)