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

Solar hydrogen peroxide (H2O2) 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 H2O2 in an efficient way. Herein, we report that polyterthiophene (pTTh), a metal-free narrow-bandgap polymeric semiconductor, is an efficient photocathode for H2O2 production in alkaline solution. We found that 2e(-) selectivity for the ORR is dependent on the pH of electrolytes and approaches 100% at pH similar to 13. A record-high H2O2 concentration of 110 mmol L-1 is achieved, which is two orders of magnitude higher than the previous photosynthesized H2O2. Furthermore, NiFeOx/BiVO4-pTTh dual-photoelectrodes in photoelectrochemical devices enabled bias-free synthesis of solar H2O2 of concentration similar to 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 similar to 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.