ZnO Nanosheets Decorated with Graphite-Like Carbon Nitride Quantum Dots as Photoanodes in Photoelectrochemical Water Splitting

Abstract

The efficient utilization of solar power is becoming an important strategy for its conversion into a storable, clean, and renewable energy source like H2. To generate H2 as a chemical fuel from solar power, attempts are being made to establish photoelectrochemical (PEC) water splitting as an efficient, greener pathway. Here, the surfaces of ZnO 2D nanosheets are adorned by graphite-like carbon nitride (g-C3N4) quantum dots (QDs) with the intention of developing efficient photoanodes. Sensitization of ZnO nanosheets with C3N4 QDs leads to a more enhanced PEC performance than that of bare ZnO. The observed enhancement in PEC is due to the high light absorbance and photon-generated charge-carrier separation. The best-obtained ZnO/C3N4 photoanode exhibits a nearly 2.29 times as high photocurrent density compared to bare ZnO. ZnO 2D sheets can generate a photocurrent density of 0.414 mA cm–2 at 0.5994 V versus reversible hydrogen electrode (RHE), whereas ZnO/C3N4 can produce 0.952 mA cm–2 at 0.5994 V versus RHE under uninterrupted conditions of light illumination. Further, there is improvement in the observed PEC activity of the heterostructure because of enhancement in the carrier density. The carrier density enhances nearly 2.2 times in the heterostructure compared to the bare ZnO sheet. ZnO/C3N4 shows a maximum photoconversion efficiency (η) of 0.70%. Both ZnO 2D sheets and the ZnO/C3N4 heterostructure show efficient stability under chopped irradiation of light for 1000 s. The stability of ZnO/C3N4 is also determined for 1 h under continuous illumination.