A template-free method to synthesis high density iron single atoms anchored on carbon nanotubes for high temperature polymer electrolyte membrane fuel cells

Highlights: • A template-free method to synthesis high density iron single atoms supported on highly conductive carbon nanotubes. • The loading of iron single atoms can reach 3.5 wt% homogeneously supported on carbon nanotubes. • The carbon nanotubes supported iron single atoms shows a half-wave potential of 0.801 V for ORR in 0.1 M HClO₄ electrolyte. • The iron single atom catalyst exhibits a E_1/2 of 27 mV higher than that of Pt/C in 0.2 M H₃PO₄ + 0.1 M HClO₄ electrolyte. • The iron single atom catalysts as the cathode catalyst in HT-PEMFC delivers a peak power density of 266 mW cm^‐2 at 240 °C that is comparable to Pt/C. Carbon supported iron single atom catalysts (FeSA) are promising materials to replace precious and expensive Pt catalysts for oxygen reduction reaction (ORR) in high temperature polymer electrolyte membrane fuel cells (HT−PEMFCs). However, to support high density of atomic iron active sites on conductive carbon supports, such as carbon nanotubes (CNTs), relies on templates to avoid aggregation of iron atoms. Here, a simple and template-free method has been developed to prepare high density iron single atoms supported CNTs. The FeSA with an atomic Fe loading of 3.5 wt% shows an onset potential (E_on) of 0.95 V and a half-wave potential (E_1/2) of 0.801 V for ORR in O₂-saturated 0.1 M HClO₄ solution, which is comparable to that of Pt/C (Pt loading of 25 μg_Pt cm⁻²). The high ORR performance is resulted from the high-density atomic sites and the highly conductive CNTs-graphene networks. Most importantly, the FeSA exhibits a E_1/2 of 0.80 V, 27 mV more positive than that of Pt/C in 0.2 M H₃PO₄+0.1M HClO₄ electrolyte due to its high phosphate resistance ability. The applicability of as-synthesized FeSA catalysts as precious metal group (PGM)-free cathode has been demonstrated in a HT-PEMFC, delivering a peak power density of 266 mW cm⁻² and excellent stability at 240 °C using anhydrous H₂ as fuel. The method provides a facile and practical route for developing highly efficient PGM-free catalysts for HT−PEMFCs.