Developing non platinum group metal electrocatalyst for oxygen reduction reaction derived from metal-organic-frameworks precursors

Pt-based materials are the state-of-the-art catalysts in full cells [1]. However, the scarce reserve, high cost, poor durability, and low poison resistance significantly prohibit their large-scale commercial application [2]. Hence, great efforts have been made to develop low cost, highly active, and high-performance non-precious metal catalysts (NPMCs) for the oxygen reduction reaction (ORR), including alloys [3], metal oxides [4], and heteroatom-doped carbons [5]. Among them, transition-metal–nitrogen–carbons (TM-N-C, TM = Mn, Fe, Co, Ni, etc.) have been considered as promising candidates because of their low cost, comparable catalytic activity and durability [6]. Such electrocatalyst can be obtained from different precursors, but one of attractive materials which have been used recently are metal–organic frameworks (MOFs) precursors. Some unique features that distinguish MOFs from other materials include well-defined crystal structure, large and adjustable surface area, ultrahigh porosity, and variety in the synthetic chemistry [7, 8]. One of the extensive applications of MOFs are in catalysis field, but they still suffer from difficulties including poor conductivity and facile collapse during solvent extraction. To overcome these obstacles, MOFs can be used as a precursor to synthesize MOF-related nanomaterials by carbonization of MOFs at high temperatures in inert atmosphere that the result of this action is produce microporous carbon materials with high surface area which increases active sites and benefits mass transfer [9, 10]. In other words, compared with the traditional precursors to synthesis of NPMCs, MOFs are particularly suitable for electrochemical applications. Because in this 14th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 12- 13 Dec, 2018 275 material, there is an inherent coordination between metals, heteroatoms and carbon into one framework that eliminating tedious extra-treatment synthesis steps for heteroatom-doping, and there is homogeneous dispersion of metal-heteroatom doping throughout framework which can serve as active sites and increase ORR performance. One of the effective strategies to lead up promising ORR performance is synthesis approach deviation to encapsulated metal/inorganic NPs in the graphitic carbon shells, such as carbon nanotubes (CNTs). In this way, a charge transfer from the metal NPs cluster to the carbon nanotubes takes places and this modification is expected to decrease the local work function and increase the chemical reactivity of the functionalized region of the CNTs exterior. It has been demonstrated that in such electrocatalyst derived from MOF, catalytic activity and their stability can be improved especially in harsh acidic medium.