Abstract
Understanding of less-noble-metal (M) dissolution from Pt-alloy-based oxygen reduction reaction (ORR) electrocatalysts, as well its interaction with Pt surface, is crucial for maximizing their performance. In pursuing this goal, two ORR electrocatalysts—a benchmark Pt–Co/C and an in-house designed Pt–Cu/C materials—are investigated. Both are characterized with a range of standard techniques, such as X-ray diffraction (XRD), transmission electron microscopy (TEM) combined with energy dispersive spectroscopy (EDX) and thin film-rotating disc electrode (TF-RDE) measurements. A special focus is put on combining the latter with a highly sensitive electrochemical flow cell (EFC) online connected to inductively coupled plasma mass spectrometry (ICP-MS) measurements. A combination of standard and novel techniques provides unprecedented insights into the dissolution behavior and dynamics of metals, as well as their subsequent surface interactions and effects on the electrochemical performance. A special focus is d...
Highlights
Being one of the cornerstones of the sustainable energy politics, hydrogen technology is believed to play an essential role in the near future
One of the major drawbacks of Pt-alloy (Pt−M) electrocatalysts is the insufficient stability of M at the oxygen reduction reaction (ORR) working potentials in acidic proton exchange membrane fuel cells (PEMFC) environment,[9] which results in leaching/ dealloying of M.10−12 some corrosion is initially even desired to form a Pt-rich overlayer over the PtMx core and enhance the ligand and/or strain effect, any further corrosion especially in the membrane electrode assembly (MEA) environment leads to significant drop of ORR specific activity.[13]
The main conclusions are as follows: (i) Both electrocatalysts lose significant amounts of their less-noblemetal component (Co or Cu) during the electrochemical activation protocol. While this was fully expected for the “as prepared” Pt−Cu/C electrocatalyst, the result is rather surprising for the “as received” Pt−Co/C electrocatalyst which had already been ex situ activated by the producer. (ii) In the case of Pt−Cu/C electrocatalyst, potential-holdactivated electrocatalyst leaks about an order of magnitude more less-noble-metal during each cycle in contrast to the potential-cycling-activated electrocatalyst. This can lead to high enough less-noble-metal concentrations to affect the corresponding electrochemical reactions - due to either noncovalent or thermodynamic (UPD) interactions. (iii) In the case of Pt−Cu/C electrocatalyst, the degree of less-noblemetal leakage influences ORR because of the Pt-M (UPD) interaction
Summary
Being one of the cornerstones of the sustainable energy politics, hydrogen technology is believed to play an essential role in the near future. Low-temperature proton exchange membrane fuel cells (PEMFC), together with batteries, are expected to compete with and eventually replace conventional energy infrastructure.[1] In the recent years, two major challenges, such as high cost of Pt and sluggish kinetics of the cathode oxygen reduction reaction (ORR), have been successfully tackled,[2] bringing this technology on the doorstep of commercialization.[3] The progress is mainly attributed to the successful use of nanoparticulate Pt-based alloys (Pt−M) with less expensive 3d transition metals (M = Cu, Co, and Ni to mention the most common ones), which are currently considered as state-of-the-art ORR electrocatalysts They enable better utilization of Pt atoms by wasting a lower number of core Pt atoms inside the nanoparticles[4] but can substantially enhance ORR specific activity by the well-known ligand or strain effect.[5] This enables a decrease of the Pt loading without losses in the overall PEMFC performance and substantially reduces the cost. In a previous study by General Motors,[14]
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