Anthraquinone Redox Relay for Dye‐Sensitized Photo‐electrochemical H2O2 Production

Anthraquinone (AQ) redox mediators are introduced to metal‐free organic dye sensitized photo‐electrochemical cells (DSPECs) for the generation of H2O2. Instead of directly reducing O2 to produce H2O2, visible‐light‐driven AQ reduction occurs in the DSPEC and the following autooxidation with O2 allows H2O2 accumulation and AQ regeneration. In an aqueous electrolyte, under 1 sun conditions, a water‐soluble AQ salt is employed with the highest photocurrent of up to 0.4 mA cm−2 and near‐quantitative faradaic efficiency for producing H2O2. In a non‐aqueous electrolyte, under 1 sun illumination, an organic‐soluble AQ is applied and the photocurrent reaches 1.8 mA cm−2 with faradaic efficiency up to 95 % for H2O2 production. This AQ‐relay DSPEC exhibits the highest photocurrent so far in non‐aqueous electrolytes for H2O2 production and excellent acid stability in aqueous electrolytes, thus providing a practical and efficient strategy for visible‐light‐driven H2O2 production.