Gradient oxygen doping triggered a microscale built-in electric field in CdIn2S4 for photoelectrochemical water splitting

Construction of built-in electric field has been identified as an attractive improvement strategy in terms of photoelectrochemical (PEC) water splitting by facilitating the carriers extraction from the inside to the surface. However, the promotion effect of the electric field is still restrained by the confined built-in area. Herein, we construct a microscale built-in electric field via the gradient oxygen doping. Octahedral configuration of the synthesized CdIn2S4 (CIS) behaves as a structural basis, which enables the subsequent oxygen doping poking to the depth of ~100 nm. Accordingly, oxygen doped CIS (OCIS) photoanode exhibits a microscale built-in electric field with the band bending. An excellent PEC catalytic activity with a photocurrent density of 3.69 mA/cm2 at 1.23 V vs RHE is achieved by OCIS, which is 3.1 times higher than that of CIS. Combining the results of sufficient characterizations and theoretical calculation, accelerating migration and separation of charge carriers has been determined as the essential encouragement. Meanwhile, probable recombination risk at the doping centers has also been reduced to the minimum via optimal experiments. This work provides a new generation idea of build-in electric field from the view point of bulky configuration towards PEC water splitting.