Activating Ni atoms up to the third nearest neighbor around single-atom Fe into highly active sites for PGM-free anion-exchange membrane fuel cells

Abstract

Anion exchange membrane fuel cells (AEMFCs) have attracted much attention due to their bipolar design that enables the use of all Pt-group metal (PGM)-free catalysts. As the only PGM-free metal with the anode hydrogen oxidation reaction (HOR), the performance of Ni-based metals in fuel cells is too low to match well with the cathode oxygen reduction reaction (ORR) due to the low utilization rate of the active sites. Here, we activated Ni atoms with single-atom Fe up to its third nearest-neighbor site, and the prepared catalyst Fe₁Ni single-atom alloy (named Fe₁Ni_SAA–O@CN) exhibited a high mass activity of 67.58 A g_Ni⁻¹. More importantly, the peak power density (PPD) of the AEMFC with an Fe₁Ni_SAA–O@CN/C anode reached 729.4 mW cm⁻², which was 4.4 times that of pure Ni, exceeding most of the previously reported Ni-based anode catalysts. Furthermore, when this catalyst was paired with a PGM-free cathode catalyst, a remarkable PPD of 420.9 mW cm⁻² was obtained, highlighting the outstanding performance of the catalyst. Atomic resolution electron energy-loss spectroscopy (EELS) analysis and density functional theory (DFT) calculations revealed that the surrounding Ni atoms up to the third nearest neighbor around the Fe dopants were tuned into active sites via charge transfer from the Fe, thereby increasing the HOR activity. This study provides a new design paradigm for further improving the performance of PGM-free AEMFCs.