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.