Boosting the activity of non-platinum group metal electrocatalyst for the reduction of oxygen via dual-ligated atomically dispersed precursors immobilized on carbon supports

Highlights: • Single atom oxygen reduction reaction electrocatalysts were synthesized from bidentate ligated metal organic frameworks. • Dual-ligand approach facilitated the control of distance between single atoms for high density distribution of active sites. • Immobilizationon conductive carbon improved the dispersion of single atoms and the formation of dispersed metal ion centers. • Single Fe atom catalyst has a high ORR activity with an onset potential of 0.96 V and a half-wave potential of 0.84 V in acid. This paper describes the use of both atomically dispersed precursors (ADPs) and conductive carbon dispersion towards the synthesis of iron-based single atom electrocatalysts for the oxygen reduction reaction (ORR). For non-platinum group metal (non-PGM) catalysts, single iron, cobalt or manganese atoms coordinated with nitrogen are the most active structures towards the ORR. Achieving a high density of active sites made of single atoms is still challenging, requiring careful controls of pyrolysis to reduce the sintering of metal active sites. Herewith, we present a new strategy to synthesize iron-based single atom ORR electrocatalysts using a two-pronged approach. We first designed a dual-ligated metal organic framework (MOF) precursor. This MOF was then immobilized onto Ketjen black carbon that serves as a conductive dispersion medium for creating the highly dispersed single atom sites. We demonstrate a near complete dispersion of the iron sites without obvious formation of nanoparticles. The activity of the resulting electrocatalyst exhibited an onset potential of 0.96 V and a half-wave potential of 0.84 V vs. reversible hydrogen electrode (RHE).