Stabilization of platinum–nickel alloy nanoparticles with a sulfur-doped graphene support in polymer electrolyte membrane fuel cells

Abstract

Polymer electrolyte membrane fuel cells (PEMFC) are limited by the sluggish oxygen reduction reaction (ORR) at the cathode, necessitating the use of platinum-based catalysts for practical use. However, such catalysts suffer from degradation issues related to the catalyst and the support material that prevent prolonged operation. Sulfur-doped graphene (SG) as a catalyst support material promises high durability with pure Pt, but its contribution to lattice-strained Pt as in bimetallic alloys has not yet been determined. In this work, platinum–nickel alloy nanoparticles with SG are synthesized (denoted as Pt–Ni/SG), then chemically dealloyed (denoted as Pt–Ni/SG-DA) and finally subjected to a post heat treatment (denoted as Pt–Ni/SG-PHT). The prepared catalysts Pt–Ni/SG, Pt–Ni/SG-DA and Pt–Ni/SG-PHT are physically characterized and electrochemically tested in half-cell conditions. Pt–Ni/SG-PHT is found to be superior, exhibiting the highest ECSA and mass activity retention with losses of 27 and 28% respectively after 1500 cycles from 0.05 to 1.3 V vs. RHE in HClO₄. This is compared to a 59% ECSA loss and 69% activity loss for commercial Pt/C under the same conditions. Hence, the strong interaction between the metal particles and sulfur-doped graphene resulting from the annealing process as in Pt–Ni/SG-PHT yields a highly stable electrocatalyst for the ORR.