Solar Photoelectroreduction of Nitrate Ions on PbI2/CuI Nanocomposite Electrodes

Solar light–driven photoelectrochemical conversion of nitrate ions to nitrite is achieved on copper‐lead iodide nanocomposite electrodes. By optimizing the composition, 1.2 ± 0.05 mA cm −2 photocurrent density is obtained under concentrated solar irradiation. The reduction products are NO 2 − and N 2 , at 0.61 V reversible hydrogen electrode (RHE), which is at least 600 mV higher than the redox potential of these processes. The faradaic efficiency of NO 2 − ion formation is up to 52% while no hydrogen evolution occurs. Optical studies show the possibility of exciting electrons from the valence band of CuI to the conduction band of PbI 2 upon illumination, extending the visible light absorption of the nanocomposite photoelectrode. Experimental and theoretical optoelectronic studies indicate that CuI and PbI 2 are held together by weak attractive forces (also excluding the formation of a new compound), which opens a new strategy to design metal halide nanocomposite photoelectrodes with tailored properties.