Metal-organic-framework-derived electrocatalysts for alkaline polymer electrolyte fuel cells

Abstract

Metal-organic frameworks were used as metal-nitrogen-carbon templates to synthesize Co–N–C catalysts through a facile synthesis approach that combined a cobalt-based zeolitic imidazolate framework (ZIF) structure and conductive carbon support. The spectroscopic, structural, and thermogravimetric analysis confirmed the synthesis of the Co-based ZIF, used to prepare catalysts with different ZIF/carbon support ratios by pyrolysis under inert atmosphere. Electrochemical characterization at alkaline pH demonstrated high activity towards oxygen reduction reaction (ORR). In addition to ORR activity, the Co–N–C electrocatalysts showed high methanol tolerance in the preliminary tests in a half-cell configuration. When assembled at the cathode side of both a hydrogen-fed anion exchange membrane fuel cell and an alkaline direct methanol fuel cell (ADMFC), the Co–N–C electrocatalysts showed competitive performance with the state-of-the-art Pt/C and other platinum-group-metal-free materials, using a FUMASEP® FAA-3-50 membrane. Exceptionally high performance (higher than 45 mW cm−2) was achieved in ADMFC fed with high methanol concentration (up to 10 M), due to the high methanol tolerance of Co–N–C electrocatalysts. Normalizing the performance to Pt loading, a value of 31.0 mW mgPt−1 was obtained, which is the highest power up to now recorded with this kind of membrane and one of the highest values in the literature for ADMFCs.