Spectroelectrochemical study of the electro-oxidation of ethanol on WC-supported Pt – Part III: Monitoring of electrodeposited-Pt catalyst ageing by in situ Fourier transform infrared spectroscopy, in situ sum frequency generation spectroscopy and ex situ

In view of improved durability, the study of electrocatalyst supports for PEMFCs alternative to carbon is raising notable research interest. In this paper we investigated the oxidation of ethanol on WC-supported electrodeposited Pt, in pristine and aged conditions by: (i) electrochemical measurements, (ii) in situ spectroscopy (FTIR and sum-frequency generation spectroscopy (SFG)) carried out during the electro-oxidation of ethanol and (iii) ex situ synchrotron-based space-resolved photoelectron spectroscopy (SPEM). The complementarity of FTIR and SFG allows an insightful understanding of the electrochemical interface as a function of applied potential and catalyst ageing. In situ FTIR and SFG revealed adsorbed acetate and ethanol, in addition to linearly and bridge-bonded CO and solution-phase CO2. The Stark tuning of CO indicates that it is less strongly bonded to aged electrodes. Quantitative analysis of potential-dependent FTIR and SFG spectra reveals that the population of adsorption sites for CO, acetate and ethanol changes with ageing and correlates with loss of catalytic activity. Changes in catalyst morphology as well as Pt and WC chemical state have been pinpointed by SPEM: electrodeposited Pt nanoparticles tend to agglomerate and the distribution of oxidised and reduced forms of Pt and W correlates with the attack of the catalyst support.

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► WC-supported electrodeposited Pt shows superior ethanol electro-oxidation activity.
► In situ FTIR and SFG provide complementary molecular information on catalyst ageing.
► In situ FTIR and SFG pinpoint multiplicity of CO adsorption sites on WC-supported Pt.
► Potential-dependent coadsorption of acetate, ethanol and CO is affected by ageing.
► SPEM revealed chemical state distribution of Pt and W as a result of catalyst ageing.