Two-electron oxidation of water to form hydrogen peroxide catalysed by silicon-porphyrins

Abstract

The second most earth abundant atom incorporated meso-tetrapyridylporphyrinatesilicon(IV) (SiTPyP) as an electrochemical catalyst was newly synthesized. The two axially ligated water molecules on SiTPyP and the four meso-substituted pyridyl nitrogens suffer eight-step protonations and deprotonations. Our detailed pK_a study indicated that the two axially ligated water molecules were fully deprotonated to exist as O⁻–Si–O⁻ under the condition of pH > 2. Under basic conditions, SiTPyP(O⁻)₂ exerted the two-electron oxidation of water to form hydrogen peroxide as the primary product in aqueous acetonitrile, which was initiated through a one-electron oxidation process on the electrode with faradaic yield of 84–92%.