Active and Stable Oxygen Reduction Catalysts Prepared by Electrodeposition of Platinum on Mo₂C at Low Overpotential

Decreasing the cost and improving the durability of polymer electrolyte membrane fuel cell (PEMFC) electrodes are two major unresolved challenges. Electrodeposition of low-dimensional Pt on transition metal carbide supports could be a way to simultaneously address both issues. Synthesis of low-dimensional Pt typically requires expensive equipment or techniques that are difficult to reproduce or scale. An electrodeposition-based technique to accomplish this goal is therefore highly desirable. The strong adhesion energy between Pt and the C sites on the α-Mo2C surface suggests that an electrochemical technique could be exploited for this purpose. Here, PtCl62– was electrodeposited onto an α-Mo2C support at low and high overpotentials (η). A dramatic increase in the electrochemical surface area and the mass activity of the oxygen reduction reaction (ORR) was observed when Pt was deposited at low overpotentials (+8 and +18 mV vs SCE) as compared to high overpotentials (−67 and −92 mV vs SCE). Indeed, catalysts prepared in the low-overpotential region achieved an ORR mass activity of 275 A/gPt and broke the linear relationship between mass activity and loading typically exhibited by these materials. Furthermore, catalysts prepared in the low-overpotential region exhibited superior stability out to 5000 cycles in an accelerated stress test (AST) as compared to samples prepared at higher overpotentials or by chemical reduction of Pt onto α-Mo2C and carbon supports.