PEMFCs have long been considered to be among the most promising next-generation energy conversion systems for portable devices and transportation vehicles due to their zero or low pollution, high power density and low temperature operation^1,2. However, the widespread commercialization of PEMFCs remains challenged by the high cost of cell components and limited cell durability. Therefore, there is a significant need to develop new catalyst materials with high intrinsic oxygen reduction reaction (ORR) activity and stability, as well as a fabrication process that leads to high cell performance and durability with low catalyst loadings.

In this work, we investigate the activity and stability of Pt-Ni nanocage oxygen reduction electrocatalysts (Figure 1a) both ex-situ and in-situ in an operating PEMFC. Ex-situ, the catalysts were both physically and electrochemically characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and both cyclic and linear sweep voltammetry using a rotating disk electrode (RDE). The nanocages showed 2 and 4 times greater specific and mass activity than Pt/C, respectively, for the ORR with high durability.

The catalysts were transitioned from the RDE platform to operating PEMFCs by application onto a Nafion® 212 membrane to form a catalyst-coated membrane (CCM) with a low cost, custom-built air-assisted cylindrical liquid jet spraying system (ACLJS). Several ACLJS parameters were investigated and the optimized parameters were used to produce CCMs that were tested by scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), electrochemical impedance spectroscopy (EIS), PEMFC polarization and cyclic voltammetry. The CCM prepared with the Pt-Ni nanocage catalyst showed no obvious Pt and Ni dissolution and redeposition in the membrane even after 30K cycles. The performance and mass activity retention of the Pt-Ni nanocage catalyst was far superior to commercial Pt/C and just short of the US Department of Energy (DOE) 2020 targets³ (Figure 1 b,c), suggesting that Pt-alloy nanocages are very promising candidates for high-performing commercial PEMFCs.

References:

1. Service, R. F. FUEL CELLS: Shrinking Fuel Cells Promise Power in Your Pocket. Science (80-. ). 296, 1222–1224 (2002).

2. CLEGHORN, S. Pem fuel cells for transportation and stationary power generation applications. Int. J. Hydrogen Energy 22, 1137–1144 (1997).

3. (U.S. Department of Energy). Fuel Cell Technical Team Roadmap. Usdrive 9 (2013).