Single Atom Hot-Spots at Au–Pd Nanoalloys for Electrocatalytic H₂O₂ Production

Abstract

A novel strategy to direct the oxygen reduction reaction to preferentially produce H(2)O(2) is formulated and evaluated. The approach combines the inertness of Au nanoparticles toward oxidation, with the improved O(2) sticking probability of isolated transition metal "guest" atoms embedded in the Au "host". DFT modeling was employed to screen for the best alloy candidates. Modeling indicates that isolated alloying atoms of Pd, Pt, or Rh placed within the Au surface should enhance the H(2)O(2) production relative to pure Au. Consequently, Au(1-x)Pd(x) nanoalloys with variable Pd content supported on Vulcan XC-72 were prepared to investigate the predicted selectivity toward H(2)O(2) production for Au alloyed with Pd. It is demonstrated that increasing the Pd concentration to 8% leads to an increase of the electrocatalytic H(2)O(2) production selectivity up to nearly 95%, when the nanoparticles are placed in an environment compatible with that of a proton exchange membrane. Further increase of Pd content leads to a drop in H(2)O(2) selectivity, to below 10% for x = 0.5. It is proposed that the enhancement in H(2)O(2) selectivity is caused by the presence of individual surface Pd atoms surrounded by gold, whereas surface ensembles of contiguous Pd atoms support H(2)O formation. The results are discussed in the context of exergonic electrocatalytic H(2)O(2) synthesis in Polymer Electrolyte Fuel Cells for the simultaneous cogeneration of chemicals and electricity, the latter a credit to production costs.

Understanding the synergistic effects of gold bimetallic catalysts

“…The synergistic effect between the isolated single atom and the host cluster has also been found in other reactions, such as acetoxylation of ethylene to vinyl acetate [116], selective oxidation of glycerol to glyceric acid [117], aerobic oxidation of alcohols [118], and electrocatalytic production of H 2 O 2 [119]. In these reactions, the role of single atoms of impurity is to limit the byproduct formation, thus improving the selectivity toward the desired reaction pathway and the stability against being poisoned by byproducts.…”

Combining theory and experiment in electrocatalysis: Insights into materials design

“…Although several catalysts such as Pt (144), Ag (145), Au (146), Au-Pd alloys (146), nitrogen-doped carbon (147) and hierarchically porous carbon (148) have been explored, they were only found to exhibit modest 14 performance in the production of hydrogen peroxide. Suitable electrocatalysts would need to possess high selectivity towards the 2-electron as opposed to the 4-electron pathway.…”

Trends in the Electrochemical Synthesis of H2O2: Enhancing Activity and Selectivity by Electrocatalytic Site Engineering

“…Notably, pure Ag has a high activity for this reaction, similar to that of Pt−Hg. All these materials are more active than Aubased catalysts, which have been extensively investigated in previous studies; 7,28,29 Pt−Hg, Ag, and Ag−Hg exhibit an order of magnitude improvement over Au, whereas the activity of Pd−Hg is 2 orders of magnitude higher.…”