Direct Electrochemical Storage of Solar Energy in C‐Rich Polymeric Carbon Nitride Cell

Abstract

Covalent carbon nitrides (CNs) have been widely used in photocatalysis and energy storage for their graphitic 2D structure and semiconducting properties. However, carbon nitrides, normally with a bandgap of 2.7 eV, can absorb only the ultraviolet and blue fraction of solar spectrum (λ < 450 nm), limiting their performance in photovoltaic applications. Herein, a carbon‐rich polymeric carbon nitride (CPCN) with an optical bandgap of 1.74 eV and significant absorption to the visible light (550–700 nm) is reported. The dark blue CPCN serving as the photoelectrode in a monolithic photoelectrochemical solar cell successfully demonstrates direct solar‐to‐electric energy conversion and storage in one single material. Under the irradiation of simulated AM1.5 solar light, the cell generates a short‐circuit photocurrent density (Jsc) of 1.3 mA cm−2 and open‐circuit photovoltage (Voc) of 500 mV. The increase in the charge capacity of the cell has a linear dependence with the power of the incident light and the maximum specific charge capacity of 4.77 C g−1 is obtained. The transmission electron microscopy (TEM), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and Fourier infrared spectroscopy (FTIR) as well as photoelectrochemical measurements reveal the underlying mechanism of the observed light‐induced charge storage of the CPCN.