Silicon-based heterojunction photoanodes modified with copper-bipyridine catalyst for enhanced solar-driven water splitting

In photoelectrochemical (PEC) water splitting, accelerating the carrier transfer from the semiconductor to the catalytic functional layer through the construction of nanostructure-heterojunction interface is an effective method to overcome the intrinsically slow kinetics of the photoanode phase interface. In this work, p-type NiO and n-type TiO2 layers were deposited on the surface of n-type Si electrodes, respectively, to construct p-n and n-n heterojunction photoanodes. Moreover, a copper-bipyridine molecular catalyst, namely Cu(dcbpy), was deposited on the heterojunction photoanodes to furtherly provide transfer path for the photogenerated holes in water splitting. Under the illumination of simulated sunlight, the Si/NiO/Cu(dcbpy) photoanode exhibits a high photocurrent density of 16.63 mA cm−2 at 2.2 VRHE, which is 277.2 times of n-Si and 1.92 times of Si/TiO2/Cu(dcbpy) at the same condition. This result indicates that p-n heterojunction accelerates the photogenerated holes transfer from Si to the electrocatalyst of Cu(dcbpy) to achieve a high water-splitting efficiency. This work provides an approach to designing efficient Si-based photoanodes through nanostructure-heterojunction interface engineering and molecular catalyst modification.