Efficient hydrogen peroxide synthesis by metal-free polyterthiophene via photoelectrocatalytic dioxygen reduction

Solar hydrogen peroxide (H 2 O 2 ) produced through the selective two-electron (2e − ) oxygen reduction pathway is an ideal alternative to liquid fuel in addition to being a versatile chemical. Up to now, low photocatalytic activity, low selectivity and serious competing reactions have been big hurdles in the production of solar H 2 O 2 in an efficient way. Herein, we report that polyterthiophene (pTTh), a metal-free narrow-bandgap polymeric semiconductor, is an efficient photocathode for H 2 O 2 production in alkaline solution. We found that 2e − selectivity for the ORR is dependent on the pH of electrolytes and approaches 100% at pH ∼ 13. A record-high H 2 O 2 concentration of 110 mmol L −1 is achieved, which is two orders of magnitude higher than the previous photosynthesized H 2 O 2 . Furthermore, NiFeO x /BiVO 4 –pTTh dual-photoelectrodes in photoelectrochemical devices enabled bias-free synthesis of solar H 2 O 2 of concentration ∼90 mmol L −1 for several cycles without any noticeable decay. This extremely high 2e − selectivity is attributed to the intrinsic electrochemical properties of pTTh. Theoretical calculations suggested that the selectivity-determining step in the 2e − process is over ∼200 times faster than that in the 4e − pathway. Our work paves an alternative way of generating liquid solar fuel that is very promising for practical applications.