Low-loading Pt nanoparticles combined with the atomically dispersed FeN4 sites supported by FeSA-N-C for improved activity and stability towards oxygen reduction reaction/hydrogen evolution reaction in acid and alkaline media

Abstract

Reducing the loading of Pt precious metal is the promising pathway to positively promote the large-scale application for fuel cells and water electrolysis. In this work, a composite bifunctional electrocatalyst (named Pt@FeSA-N-C) consisting of the atomically dispersed FeN4 active sites and Pt nanoparticles (NPs) is successfully prepared for oxygen reduction reaction (ORR) and hydrogen evolution reactions (HER). In the process of synthesizing precursor of Pt(OH)4-Fe-Ppy@CNFs, the Fe-Ppy@CNFs was firstly prepared where the highly dispersed Fe3+ ions were pre-anchored into polypyrrole (PPy) matrixes through in-situ polymerization on the surface of cellulose nanofibers (CNFs) and then Pt(OH)4 nano-particles were deposited on Fe-Ppy@CNFs through adjusting the pH of the solution by urea hydrolysis to obtain the Pt(OH)4-Fe-Ppy@CNFs. Compared with the commercial 20 wt.% Pt/C, the obtained Pt@FeSA-N-C possesses 5.5 wt.% low Pt loading. The strong synergistic effect of dual active sites between Pt NPs and FeN4 on one-dimensional (1D) FeSA-N-C support with a large surface area ensures effectively exposure of Fe and especial Pt active sites in the Pt@FeSA-N-C. Both ORR and HER activities of the Pt@FeSA-N-C were greatly improved in acid and alkaline media, even outperforming the commercial 20 wt.% Pt/C. Furthermore, the Pt@FeSA-N-C shows an unordinary stability, with no obvious decrease in the current density after 5000 and 1000 cycles of accelerated durability tests (ADTs) for ORR and HER processes, respectively. This work highlights a preparation strategy for the synergistic effect between low-loading Pt precious metal and non-precious metals in electrocatalytic system.