Role of Electrode Thickness in NiFe Nanogranular Films for Oxygen Evolution Reaction

Ciambriello L., Cavaliere E., Vassalini I., Alessandri I., Ferroni M., Leoncino L., Brescia R., Gavioli L.

ELECTROCHEMICAL EVOLUTION  Coatings and Films  Hydrogen  Surfaces  General Energy  WATER OXIDATION  Electronic  OXIDE CATALYSTS  NICKEL-OXIDE  ELECTROCATALYSTS  Optical and Magnetic Materials  ENERGY-CONVERSION  REDOX STATES  Nanogranular materials  electrodes for oxygen evolution reaction  NiFe alloyed nanoparticles  INTRINSIC ACTIVITY  METAL  Settore FIS/01 - FISICA SPERIMENTALE  Settore FIS/03 - FISICA DELLA MATERIA  IN-SITU  Physical and Theoretical Chemistry 

Nanostructured materials may provide a route to overcome the electrode-limiting performance in water splitting, the oxygen evolution reaction (OER), within the framework of low-cost catalysts search. However, for alloyed NiFe nanostructures, the relationship among the OER efficiency and the electrode physical characteristics (morphology, porosity, size, thickness, or mass loading) is largely unknown. This work introduces a new type of alloyed NiFe (90/10% at) nanogranular electrodes obtained by supersonic cluster beam deposition and investigates the dependence of their catalytic activity toward the OER on the film morphological and stoichiometric properties. The synthesized alloyed NiFe nanoparticles with 0.3-3.8 nm size assemble from the gas phase to form ultrathin film electrodes with thickness in the 15-88 nm range, corresponding to 5-30 mu g/cm2 mass loading. The fitting of the optical spectroscopic data by an effective medium approximation model suggests that, independent of the thickness, the films have a 20% porosity and are completely hydroxydated. The resulting catalytic efficiency is independent on the film thickness, while the turnover frequency decreases with increasing electrode loading. These data suggest that an excess of catalyst mass with respect to the OER active sites is deposited in the case of thicker electrodes and sets the 15 nm film as an upper loading limit to maximize the electrocatalyst efficiency. This study represents a crucial step toward thickness optimization of NiFe electrodes to fabricate low-cost OER catalysts.

Source: Journal of physical chemistry. C. (Online) 126 (2022): 21759–21770. doi:10.1021/acs.jpcc.2c06669

Publisher: American Chemical Society,, Washington DC , Stati Uniti d'America

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