Ultra-Rapid Electrocatalytic H 2 O 2 Fabrication over Mono-Species and High-Density Polypyrrolic-N Sites.

Electrocatalytic hydrogen peroxide (H 2 O 2 ) production via two-electron oxygen reduction reaction (2e - -ORR) features energy-saving and eco-friendly characteristics, making it a promising alternative to the anthraquinone oxidation process. However, the common existence of numerous 2e - -ORR-inactive sites/species on electrocatalysts tends to catalyze side reactions, especially under low potentials, which compromises energy efficiency and limits H 2 O 2 yield. Addressing this, a high surface density of mono-species pyrrolic nitrogen configurations is formed over a polypyrrole@carbon nanotube composite. Thermodynamic and kinetic calculation and experimental investigation collaboratively confirm that these densely distributed and highly selective active sites effectively promote high-rate 2e - -ORR electrocatalysis and inhibit side reactions over a wide potential range. Consequently, an ultra-high and stable H 2 O 2 yield of up to 67.9/51.2 mol g -1  h -1 has been achieved on this material at a current density of 200/120 mA cm -1 , corresponding Faradaic efficiency of 72.8/91.5%. A maximum H 2 O 2 concentration of 13.47 g L -1 can be accumulated at a current density of 80 mA cm -1 with satisfactory stability. The strategy of surface active site densification thus provides a promising and universal avenue toward designing highly active and efficient electrocatalysts for 2e - -ORR as well as a series of other similar electrochemical processes.