Palladium-based single atom catalysts for high-performance electrochemical production of hydrogen peroxide

Electrochemical two-electron oxygen reduction reaction (2e-ORR) offers a green route for production of hydrogen peroxide (H2O2). However, it remains a key challenge to design and develop the catalysts possessing both high activity and selectivity. Herein, we design ten Palladium-based single atom catalysts (Pd-based SACs) and report the underlying mechanisms of the activity and selectivity for 2e-ORR to produce H2O2. The intermediate of *OOH is used as a descriptor to describe the catalytic activity of 2e−/4e− ORR through a volcano diagram due to a linear scaling relationship between *OOH and *O (or *OH). We find that a defect graphene binding with one Pd single atom (C4Pd), which is thermodynamically favorable, exhibits an ultralow overpotential (0.044 V) for production of H2O2. In particular, this catalyst displays excellent activity and selectivity for H2O2 in a faintly acid or neutral electrolyte instead of alkaline. Furthermore, the Pd atomic clusters binding on defect graphene (C4Pdx, x = 2, 3, 4, 5) exhibit poor performance for production of H2O2 than that of C4Pd. The computational results reveal that the side-on adsorption configurations of O2 molecule and *H constitute the limiting factors for the selectivity of H2O2. These findings offer new insights for interpreting the mechanisms of 2e-ORR and pave the way for future designs and developments of excellent catalysts for the direct synthesis of H2O2.