Boosting photoanodic activity for water splitting in carbon dots aqueous solution without any traditional supporting electrolyte

Abstract

We present a PEC water oxidation system with boosting activity in Carbon Dots (CDs) aqueous solution directly without any traditional supporting electrolyte. For α-Fe2O3 photoanode, photocurrent was significantly enhanced by dozens of folds compared to that in Na2SO4 solution under similar conditions. Based on electrochemical impedance spectroscopy, energy alignment measurements, photovoltage decay and Mott-Schottky plot, mechanism for charge transfer and function of CDs was well characterized. As semiconductors, CDs can combine with α-Fe2O3 into heterojunction for charge separation. As electrolyte, it can induce downward shift in conduction band of α-Fe2O3, allowing for stronger driving force for charge migration. Since CDs solution possesses a negative Zeta potential, it is proposed that during PEC proceeding, static interaction between CDs and positively charged photoanodic substrate can induce a dynamic balance of CDs absorbing or desorbing on/off α-Fe2O3 surface, which accounts for fast charge transfer, boosted photocurrent and high stability in PEC water splitting.