FeN₄ Active Sites Electronically Coupled with PtFe Alloys for Ultralow Pt Loading Hybrid Electrocatalysts in Proton Exchange Membrane Fuel Cells.

Abstract

The exorbitant cost of Pt-based electrocatalysts and the poor durability of non-noble metal electrocatalysts for proton exchange membrane fuel cells limited their practical application. Here, FeN₄ active sites electronically coupled with PtFe alloys (PtFe-FeNC) were successfully prepared by a vapor deposition strategy as an ultralow Pt loading (0.64 wt %) hybrid electrocatalyst. The FeN₄ sites on the FeNC matrix are able to effectively anchor the PtFe alloys, thus inhibiting their aggregation during long-life cycling. These PtFe alloys, in turn, can efficiently restrain the leaching of the FeN₄ sites from the FeNC matrix. Thus, the PtFe-FeNC demonstrated an improved Pt mass activity of 2.33 A mg_Pt^-1 at 0.9 V toward oxygen reduction reaction, which is 12.9 times higher than that of commercial Pt/C (0.18 A mg_Pt^-1). It demonstrated great stability, with the Pt mass activity decreasing by only 9.4% after 70,000 cycles. Importantly, the fuel cell with an ultralow Pt loading in the cathode (0.012 mg_Pt cm^-2) displays a high Pt mass activity of 1.75 A mg_Pt^-1 at 0.9 V_{<i>iR</i>-free}, which is significantly better than commercial MEA (0.25 A mg_Pt^-1). Interestingly, PtFe-FeNC catalysts possess enhanced durability, exhibiting a 12.5% decrease in peak power density compared to the 51.7% decrease of FeNC.