Metal-organic framework-polymer complex-derived single-atomic oxygen reduction catalyst for anion exchange membrane fuel cells

Abstract

Metal-nitrogen-doped carbon (M−N−C) catalysts have emerged as highly active noble-metal-free catalysts for oxygen reduction reactions (ORR) in anion-exchange membrane fuel cells (AEMFCs). However, the performance of existing M−N−C catalysts is limited by the inaccessibility of internal M−Nx active sites and loss of nitrogen doping after the carbonization process. Here, a single-atom Co, Fe and N-doped porous carbon catalyst (CoFe-NC-PPy) were constructed using a complex of metal–organic frameworks (MOFs) and polypyrrole (PPy). As a new approach, we synthesized MOF and PPy composites by combining in situ MOF synthesis and pyrrole polymerization in a one-pot reaction. Through pyrolysis, the PPy and MOF composites demonstrated an enhanced specific surface area, a high active-site density, and a high concentration of nitrogen species in the M−N−C catalyst. These contributed to a superior ORR performance (E1/2 of 0.915 V) and high durability in alkaline media. Additionally, the CoFe-NC-PPy material studied in an AEMFC enabled high performance with a current density of 550 mA cm−2 at 0.6 V and a peak power density of 352 mW cm−2. This study suggests potential in combining polymers and MOFs in the synthesis of ORR catalysts for fuel cells.