A combined approach toward enhancing 2-electron oxygen reduction through the incorporation of Pd-based complex into a carbonaceous matrix: Experimental and mechanistic-theoretical studies

The present work reports the development of a catalyst based on palladium (Pd) coordination compound covered and surrounded by Printex L6 (PL6C) carbon material and its application toward improving the selectivity and electrocatalysis involving the production of hydrogen peroxide via oxygen reduction reaction (2e–ORR). The morphology and structure of the Pd-based complex/PL6C catalyst were characterized by clusters of an average size of 2.4 µm composed of 1.3% (w/w) Pd2+ metal. Compared to the unmodified PL6C, the application of the Pd-based complex/PL6C led to a shift in the ORR onset potential by 250 mV vs Ag/AgCl 3 M to more positive potentials and 97% selectivity toward H2O2 production. This electrocatalytic effect was attributed to the π-π interactions between the dz2 orbital of the Pd2+ metal and the carbon close to the oxygenated functional groups present in the carbonaceous matrix. The mechanistic-theoretical analyses conducted showed that the oxygenated carboxyl functional group COOH is the group that favors most significantly the interaction between O2 and hydronium ions toward the formation of the OOH* species; the presence of the Pd2+ metal further contributes toward favoring this interaction. In addition, the Pd-based complex was found to influence the Laplacian of the electron density (V2ρ) for the bond between the carbon close to the COOH group and the oxygen atom of the ORR intermediates, and this facilitates the conversion of adsorbed O2 species into OOH* intermediates and increases the desorption capacity of the species from the active site, leading to H2O2 formation.