Study of new electrocatalysts based on efficient and stable nanoalloys by scanning electrochemical microscopy
Abstract
Proton-exchange membrane fuel cells (PEMFC) are a possible alternative to produce energy.
However they cannot yet be used at large scale because of their low efficiency and durability.
At present, their main limitation is the performance of oxygen reduction reaction (ORR)
occurring at the cathode. This reaction still needs an overpotential of 300 to 600 mV (compared
to 20 mV for the anode) and most of the electrocatalysts conventionally used undergo
degradation and deactivation1. To reach both, good activity and stability towards ORR, various
ideas are explored in the literature based on the modification of shape, size, porosity, chemical
composition, etc2. The Palladium:Cobalt alloy (Pd:Co) has been reported in literature3 as an
interesting alternative, since exhibits good activity towards ORR. However, Co gets mainly
dissolved in acidic solution. The idea of our study to overcome this issue is to selectively
oxidize the Co surface on the Pd:Co alloy to preserve its activity while increasing its stability.
In the present communication, the Scanning ElectroChemical Microscope (SECM)4,5 is used in
pumped-Micropipette Delivery/Substrate Collection (pumped-MD/SC) mode to compare the
activity of different catalysts towards ORR. This approach gives as a result an intensity
contrasted image (i.e. Figure 1), which allows a direct comparison of multiple catalysts under
the same experimental conditions thanks to the microfabrication of the samples. Moreover, the
catalysts have been characterized by other techniques such as Electrochemical Impedance
Spectroscopy (EIS), which allows us to evaluate the thickness of the oxide layer formed and
study its stability.
(1) Ge, X. et al. ACS Catal. 2015, 5, 4643-4667
(2) Sánchez Sánchez, C. M. et al. JACS. 2010, 132, 5622-5624
(3) Fernandez, J. et al. JACS. 2005, 127, 357-365
(4) Cannan, S. et al. Phys. Chem. Chem. Phys., 2011, 13, 5403–5412
(5) Sánchez Sánchez, C. M. et al. Electrochem. Soc. Interface, 2014, 23, 43-45