We focus on the catalysis of electrochemical oxygen reduction to hydrogen peroxide. Electronic effect and geometric effect are the two important factors determining activity and selectivity of catalysts. Beyond these well-known effects, pH and mass transport of product can profoundly change the activity and the selectivity of catalyst. Activity and selectivity of Pt-Hg, Ag-Hg, Ag, and glassy carbon electrode abruptly changed by pH of reaction environment. We also highlight the importance of mass transport on benchmarking the selectivity by comparing three different systems with different mass transport phenomena, rotating ring disk electrode, stagnant electrode, and membrane electrode assembly.

We propose single-atom catalyst as a promising type of catalyst for H₂O₂ production. Single-atom catalysts exhibit intriguing catalytic properties due to its geometric arrangement where active atoms are well separated with each other, and each individual atom directly interact with support atoms. Single-atom catalyst can satisfy both electronic and geometric effect for the optimized performance. Near hundred percent noble metal utilization led to high mass activity for electrochemical H₂O₂ production.