Fe-N-C electrocatalyst with dense active sites and efficient mass transport for high-performance proton exchange membrane fuel cells

To achieve the US Department of Energy 2018 target set for platinum-group metal-free catalysts (PGM-free catalysts) in proton exchange membrane fuel cells, the low density of active sites must be overcome. Here, we report a class of concave Fe-N-C single-atom catalysts possessing an enhanced external surface area and mesoporosity that meets the 2018 PGM-free catalyst activity target, and a current density of 0.047 A cm(-2) at 0.88 ViR-free under 1.0 bar H-2-O-2. This performance stems from the high density of active sites, which is realized through exposing inaccessible Fe-N-4 moieties (that is, increasing their utilization) and enhancing the mass transport of the catalyst layer. Further, we establish structure-property correlations that provide a route for designing highly efficient PGM-free catalysts for practical application, achieving a power density of 1.18 W cm(-2) under 2.5 bar H-2-O-2, and an activity of 129 mA cm(-2) at 0.8 ViR-free under 1.0 bar H-2-air.