Photoelectrochemical Reduction of 2‐t‐Butyl‐9,10‐Anthraquinone at Illuminated P‐Type Si: An Approach to the Photochemical Synthesis of Hydrogen Peroxide

The electrochemical behavior of 2‐t‐butyl‐9,10‐anthraquinone, BAQ, has been investigated at illuminated (632.8 nm, ~50 mW/cm2) p‐type semiconducting Si in with and without added . In the absence of the BAQ is photoreducible at the photocathode to form . Relative to vs. SCE the photovoltage, at open circuit is ~0.5V. An efficiency for a regenerative photoelectrochemical cell based on the is ~4% for the conversion of 632.8 nm light. In the presence of the BAQ is photoreducible to 2‐t‐butyl‐9,10‐dihydroxyanthracene, , with a measured current efficiency of >90% when the p‐type Si photocathode is held at −0.3V vs. SCE in a two‐compartment cell. Preparative, controlled‐potential photoelectrochemical reduction of BAQ to in has been demonstrated for >90% conversion of 0.2M BAQ to . Reaction of the photoelectrochemically generated with from air yields solutions containing . The has only ~2% photoelectrochemical energy conversion efficiency. The low efficiency is apparently a consequence of sluggish electrode kinetics or adsorption problems that lead to a low with respect to the vs. SCE in the presence of .