Investigation on the structural dynamic of bimetallic PtNi alloy catalyst under operational conditions

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In the path toward the green energy transition, fuel cells play an important role together with batteries. Proton Exchange Membrane Fuel Cells (PEMFC) are a shining example in a variegated landscape due to features like high energy density and low operational temperature. However, the catalyst is still the most challenging component, and since is most commonly made of platinum, research is focused on its substitution or usage reduction. An example in this direction is the employment of bimetallic alloy catalysts where platinum (Pt) is combined with a low-cost transition metal, like nickel (Ni).

A research work led by Dr. Ivan Khalakhan and coordinated by Prof. Iva Matolínová (Charles University of Prague), with the collaboration of Prof. Konstantin Neyman (ICREA & University of Barcelona), and colleagues, investigated the phenomena that occur at the surface of a PtNi bimetallic cathode catalyst under altering oxidation-reduction environments, revealing its behaviour during operation.

Schematic representation of the experiment together with results shoving oscillatory behaviour of PtNi composition in response to altering oxidation and reduction environments

Two experimental techniques like the surface-sensitive SRPES (Synchrotron Radiation Photoelectron Spectroscopy) and the bulk-sensitive XPS (X-ray Photoelectron Spectroscopy), available at the Czech CERIC Partner Facility at Elettra Synchrotron (Material Science Beamline) were employed for samples characterisation. The experimental results, coupled with theoretical calculations, revealed that under repetitive oxidation/reduction cycles, there is an oscillatory behaviour of the surface composition of the catalyst, which led to a loss of its chemical integrity in terms of nickel surface enrichment. The enrichment of Ni species on the surface suppresses valuable properties of PtNi alloy, which is critical for its high electrocatalytic performance.

This work provided relevant insights that will help to formulate a comprehensive model of catalyst degradation in real conditions and develop a corresponding mitigation strategy leading towards a more robust catalyst for energy systems with long-lasting performances.

ORIGINAL ARTICLE:

IRREVERSIBLE STRUCTURAL DYNAMICS ON THE SURFACE OF BIMETALLIC PTNI ALLOY CATALYST UNDER ALTERNATING OXIDIZING AND REDUCING ENVIRONMENTS. KHALAKHAN I., VEGA L., VOROKHTA M., SKÁLA T., VINES F., YAKOVLEV Y. V., NEYMAN K. M. & MATOLINOVA I., (2020), APPLIED CATALYSIS B: ENVIRONMENTAL, 264, 118476.