Improved Durability and Activity in Pt/Mo₂C Fuel Cell Cathodes by Magnetron Sputtering of Tantalum

Cost reduction together with durability represent the primary challenges for cathode catalysts in polymer electrolyte membrane fuel cells (PEMFCs). The catalyst is often supported by carbon, which suffers from parasitic corrosion, particularly during start-up and shut-down operations. Transition metal carbides (TMCs) have attracted attention as a potential replacement for carbon supports because some of them have electronic structures likened to noble metals. Mo₂C has shown promising activity as platinum support for the oxygen reduction reaction (ORR) but can suffer from oxidation and dissolution. Here, Mo₂C supports are modified by surface tantalum (Ta) treatment using a variety of DC magnetron sputtering operating parameters. All supports modified by Ta showed improved corrosion resistance compared to the untreated support. Pt/Mo₂C modified with Ta using a 500 V bias, 6 mTorr working pressure, and 2 min sputter time additionally showed improved kinetic current density and mass activity. Ta sputtering under these conditions were applied to the cathode side of a Pt/Mo₂C membrane electrode assembly and showed significantly improved durability when subjected to an accelerated stress test. Ta-modified Pt/Mo₂C cathodes showed resistance to void formation and loss of electrochemical surface area. Ta magnetron sputtering can therefore be considered a viable surface treatment for improving the activity and stability of PEMFCs using Mo₂C-based supports.