In-situ Synthesis of the Thinnest In 2 Se 3 /In 2 S 3 /In 2 Se 3 Sandwich-Like Heterojunction for Photoelectrocatalytic Water Splitting.

The efficient utilization of solar energy for photoelectrocatalytic (PEC) water splitting is a feasible solution for developing clean energy and alleviating environmental issues. However, as the core of PEC technology, the existing photoanode catalysts have disadvantages such as poor photoelectrocatalytic conversion efficiency, low conductivity of photogenerated carriers, and instability. Here, we report the ultrathin two-dimensional sandwich-like (SW) heterojunction of In 2 Se 3 /In 2 S 3 /In 2 Se 3 (SW In 2 S 3 @In 2 Se 3 ) for the first time for PEC water splitting. Our findings identify the efficient separation of electrons and holes by constructing SW In 2 S 3 @In 2 Se 3 heterojunction. The in situ synthesis of ultrathin nanosheet arrays by using surface substitution of Se atom to epitaxially grow cell In 2 Se 3 maximizes the contact area of heterogeneous interface and accelerates the transmission of charge carrier. Benefitting from the unique structure and composition characteristic, SW In 2 S 3 @In 2 Se 3 displays excellent performance in PEC water splitting. The photocurrent density of SW In 2 S 3 @In 2 Se 3 reaches 8.43 mA cm -2 at 1.23 V RHE . Compared with In 2 S 3 , the SW In 2 S 3 @In 2 Se 3 photoanode has nearly 12 times higher PEC performance, which represents the best performance among the In 2 S 3 -based photoanode heterojunction reported so far. The evolution rate of O 2 reaches 78.8 μmol cm -2  h -1 , and the photocurrent has no apparent variety within 24 h.