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

Abstract

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 ∼ 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, NiFeO_x/BiVO₄–pTTh dual-photoelectrodes in photoelectrochemical devices enabled bias-free synthesis of solar H₂O₂ 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.