In Situ Deposition of Pd during Oxygen Reduction Yields Highly Selective and Active Electrocatalysts for Direct H₂O₂ Production

Hydrogen peroxide (H₂O₂) is a commodity chemical that serves as an oxidant and disinfectant for a number of historically important chemical end-use applications. Its synthesis can be made more sustainable, clean, and geographically distributed through technology enabled by the aqueous electrocatalytic two-electron reduction of O₂, which produces H₂O₂ using only air, water, and electricity as inputs. Herein results are presented establishing that Pd, which is widely known to catalyze the four-electron reduction of O₂ to H₂O, can be made highly selective toward H₂O₂ production when it is deposited in situthat is, through electrochemical deposition from Pd ions during O₂ reduction. The resultant cathodes are found to be comprised of sub-5 nm amorphous Pd nanoparticles and are measured to facilitate H₂O₂ selectivities above 95% in the relevant potential range. In addition, the cathodes are highly activethey are associated with the second-highest partial kinetic current density for H₂O₂ production in acidic media reported in the known literature. It is observed that in situ synthesis of Pd catalysts enables dramatic gains in H₂O₂ yield for all inert, conductive supports studied (including glassy carbon, commercial activated carbon, graphene, and antimony-doped tin oxide). Further efforts to generalize these results to other systems establish that even Pt, the prototypical four-electron O₂ reduction catalyst, can be engineered to be highly selective to H₂O₂ when it is synthesized in situ under relevant conditions. These results and the comprehensive electrochemical and physical characterization presented, including synchrotron-based X-ray absorption spectroscopy, suggest that in situ synthesis is a promising approach to engineer O₂ reduction electrocatalysts with tunable product selectivity and activity.