Simultaneously Geometrical and Electronic Modulation of L10-PtZn by Trace Ge Boosts High-performance Oxygen Reduction Reaction.

Abstract

Developing a highly active, durable, and low-platinum-based electrocatalyst for the cathodic oxygen reduction reaction (ORR) is for breaking the bottleneck of large-scale applications of proton exchange membrane fuel cells (PEMFCs). Herein, ultrafine PtZn intermetallic nanoparticles with low Pt-loading and trace germanium (Ge) involvement confined in the nitrogen-doped porous carbon (Ge-L10-PtZn@N-C) are reported. The Ge-L10-PtZn@N-C exhibit superior ORR activity with a mass activity of 3.04 A mg-1 Pt and specific activity of 4.69mA cm-2, ≈12.2- and 10.2-times improvement compared to the commercial Pt/C (20%) at 0.90V in 0.1m KOH. The cathodic catalyst Ge-L10-PtZn@N-C assembled in the PEMFC shows encouraging peak power densities of 316.5 (at 0.86V) and 417.2mW cm-2 (at 0.91V) in alkaline and acidic fuel-cell, respectively. The combination of experiment and density functional theory calculations (DFT) results robustly reveal that the participation of trace Ge can not only trigger a "growth site locking effect" to effectively inhibit nanoparticle growth, bring miniature nanoparticles, enhance dispersion uniformity, and achieve the exposure of the more electrochemical active site, but also effectively modulates the electronic structure, hence optimizing the adsorption/desorption of the oxygen intermediates.