Super Hygroscopic Non‐Stoichiometric Cerium Oxide Particles as Electrode Component for PEM Fuel Cells

The design of highly efficient promoters for the oxygen reduction reaction (ORR) is an important challenge in the large‐scale distribution of proton exchange membrane (PEM) fuel cells. Hygroscopic cerium oxide (CeO 2 ) is here proposed as co‐catalyst in combination with Pt. Physical chemical characterizations, by means of X‐ray diffraction, vibrational spectroscopy, morphological and thermal analyses, were carried out, demonstrating high water affinity of the synthesized CeO 2 nanoparticles. Composite catalysts (i. e., Pt : CeO 2 1 : 0.5 and 1 : 1 wt:wt), were studied by either rotating disk electrode (RDE) and fuel cell tests performed at 80 °C and 110 °C. Interestingly, the cell adopting the Pt : CeO 2 1 : 0.5 catalyst enabled the achievement of high power densities reaching ∼80 and ∼35 mW cm −2 under low relative humidity and high temperatures. This result demonstrates that tuning material surface properties (e. g. oxygen vacancies) could significantly boost the electrochemical performance of cathodes as a combined result of optimized water retention and improved ORR kinetic.