Pt alloy nanoparticles decorated on large-size nitrogen-doped graphene tubes for highly stable oxygen-reduction catalysts

Abstract

Pt alloy nanoparticles supported on Vulcan XC-72 (Pt/C) are the most effective catalysts for kinetically sluggish oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. However, significant performance degradation has been observed with the Pt/C catalysts due to agglomeration and Ostwald ripening of Pt nanoparticles largely resulting from the corrosion of carbon supports. Here, we developed a Pt alloy catalyst through annealing Pt nanoparticles deposited on nitrogen/metal co-doped large-size graphene tubes (NGTs). The in-situ formation of PtM (M: Co and Ni) alloy during the annealing process contributes to the improvement of the catalytic activity and stability. During the accelerated stress tests (AST), after 20 000 potential cycles (0.6–1.0 V vs. RHE), the retained electrochemical surface area (ECSA) of the PtM/NGT catalyst is more than 2 times larger than that of the Pt/C catalyst. As for the AST tests of carbon corrosion, after 30 000 potential cycles (1.0–1.5 V vs. RHE) at room temperature, the NGT morphologies are well maintained and no ECSA loss of this PtM catalyst is observed, indicating excellent corrosion-resistance. Even at harsher 60 °C, the PtM/NGT catalyst exhibits only insignificant loss (6 mV) of E_1/2 while the Pt/C catalyst shows significant degradation (47 mV loss in E_1/2). The improved stability of PtM/NGT catalyst is attributed to the highly graphitized NGTs and possible synergistic effects between the NGT carbon support and the PtM alloy nanoparticles.