BI-Metallic ZIF Derived Electrocatalyst for Fuel Cell /

Abstract

Fuel cells are the emerging energy conversion devices owing to their dynamic qualities. The low temperature fuel cells such as proton exchange membrane fuel cell (PEMFC) and alkaline membrane fuel cell (AMFC) are a promising alternative to fossil fuels for powering future vehicles. Oxygen electrochemistry involves oxygen reduction (ORR) and evolution reactions. For ORR development of highly efficient non-noble metal catalysts to improve the sluggish reaction kinetics is of high significance. In this work Zeolitic Imidazolate Framework (ZIF) derived catalyst which can provide hollow framework of nitrogen doped nano porous carbon with promising ORR activity have been developed for both PEMFC and AMFC. High performance electrocatalysts for oxygen reduction reaction (ORR) in fuel cells with low Pt consumption are significant for the commercial application of PEMFCs. The current study Zeolitic Imidazolate Framework (ZIF), which can provide hollow framework of nitrogen doped nano porous carbon with promising ORR activity. In this study, we report a bimetallic pyrolyzed NiCo-ZIF supported fine Pt/Pt alloy electrocatalyst for ORR. After pyrolysis, nano-porous carbon is obtained with well dispersed Pt/Pt alloy nanoparticles (~ 3nm). This catalyst shows superior catalytic activity and stability in acid than the commercial Pt/C catalyst. As a cathode in single cell PEMFC, it gives high peak power density of 1070 mW. cm-2 at 70 oC with a low cathode platinum loading of 0.12 mg cm-2. The enhanced activity and durability can be attributed to the synergistic effect from the nitrogen doped nano-porous carbon derived from NiCo-ZIF and the defect rich carbon support to anchor Pt/Pt alloy nanoparticles. For alkaline membrane fuel cell, synthesis of nitrogen doped carbon XX nanotubes (NCNTs) derived from Zeolitic Imidazolate Frameworks (ZIFs) and their activity towards (ORR) in alkaline medium are studied. The NCNTs showed excellent ORR performance in KOH with onset potential of 0.92 V and current density of -5.6 mA.cm-2. The enhanced electrochemical activity and stability is attributed to the synergetic effect of the nitrogen doped carbon nanotubes and the Ni/Co active sites. The alkaline fuel cell performance of the membrane electrode assembly (MEA) prepared with NCNTs as cathode was 65 mWcm-2, which was higher than the MEA prepared with Pt/C as cathode (60 mWcm-2). These results indicate that NCNTs are highly efficient and durable as electrocatalysts for ORR in alkaline fuel cell. The exceptional electrocatalytic activity might be mainly attributed to the chemical composition and structure of the crystalline NCNTs formed, as well as their robust overall framework structure. This study opens up a new avenue for developing highly active MOF-derived electrocatalysts for different fuel cell applications and paving the way for their commercialization.