(65a) Carbon-Free Platinum Bismuth Alloy Nanoplatelets with Enhanced Activity and Platinum Stability in Operating Proton Exchange Membrane Fuel Cells and Electrolyzers

Hydrogen-powered proton exchange membrane fuel cells (PEMFCs) provide a clean power source for electric vehicles, domestic power plants, and other applications. Their high power density, high energy-conversion efficiency, low working temperature, and low environmental impact can significantly reduce reliance on fossil fuels. However, long-term electrode durability under operating conditions remains a significant challenge to fuel cell commercialization. Corrosion of the underlying electrocatalyst carbon support is a key issue at potentials greater than 0.9 V. Precious metal Pt dissolution and aggregation dominates at lower voltages. Both phenomena yield reduced catalyst area and loss of performance. Alloying Pt with a nonprecious transitional metal (M = Fe, Co, Ni, Cu, and Zn etc.) has been shown to enhance Pt electrocatalytic activity and stability in lab-scale tests. In the past decade, numerous studies have shown that platinum-based binary alloy electro-catalysts, such as PtFe, PtCo, PtNi, PtZn, and PtCu, exhibit enhanced oxygen reduction reaction (ORR) activity in acid electrolyte at beginning of life. However, the use of carbon supports during synthesis of these materials is ubiquitous and loss of activity under operating condition remains unresolved.

In this work, we report on the ORR activity of carbon-free Pt2Bi alloy nanoplatelets (PtBi NP) synthesized via a sustainable, all-aqueous colloidal synthesis route which are found to exhibit previously unrealized long-term stability toward Pt area loss. Beginning of life specific and mass activities of 1.81 A m^-2Pt and 402 A g^-1Pt were achieved at 0.9 V in perchloric acid; which are 7.1 and 3.1 times higher than those of commercial Vulcan-supported Pt/C, respectively. More significantly, after 10000 potential cycles in accelerated durability testing, the PtBi NP demonstrate no degradation in mass activity, half-wave potential, Tafel slope and electrochemical surface area (ECSA). Such behavior is attributed to a shift in the Pt d-band center observed via XANES which weakens oxygen binding to the catalyst surface and reduces Pt corrosion, consistent with theoretical DFT calculations. The oxophobic PtBi NP also exhibit favorable oxygen evolution reaction (OER) activity for electrolyzer operation with small charge transfer resistance, over-potential, and Tafel slope. Operating performance and durability data consistent with fundamental laboratory findings is presented at 25 cm2 scale.