Insight on Shallow Trap States in Boosting Electrochemiluminescence of Carbon Nitrides

Highly efficient interconversion of different types of energy plays a crucial role in both science and technology. Among them, electrochemiluminescence (ECL), an emission of light excited by electrochemical reactions, has drawn attention as a powerful tool for bioassays of clinical biomarkers. Nonetheless, the quantitative description of the charge transfer kinetics within the emitter, crucial for understanding and enhancing ECL efficiency, remains elusive (ΦECL). Here, we investigated the intercalation of CN using Au nanoparticles and single atom (Aux-CN), and the boosted charge carrier dynamics kinetics during ECL over time scales ranging from femtoseconds to seconds. Operando electrochemical impedance spectroscopy, fs-transient absorption spectroscopy, transit open circuit photovoltage and density functional theory calculations jointly disclosed Au-N bonds endowed shallow trapped electron states, which reconciled the timescale of the fast electron transfer in the bulk emitter and slow reduction of S2O82. It ultimately accelerated the recombination rate for electron-hole pairs and further promoted the ECL performance of Aux-CN photoelectrode. As a result, Aux-CN showed a four-fold enhancement of ΦECL compared to the pristine CN, setting a new cathodic ΦECL record among metal-free ECL emitters and endowing a visual ECL sensor for nitrite ion, a typical environmental contaminant, with superior detection range and limit.