Interfacial-electric-field guiding design of a Type-I FeIn2S4@ZnIn2S4 heterojunction with ohmic-like charge transfer mechanism for highly efficient solar H2 evolution

Manipulating charge transfer pathways in Type-I heterojunctions is essential to address the mismatched energy bands and the often-neglected internal electric field (IEF). This study reports the successful engineering of a Type-I FeIn2S4@ZnIn2S4 heterojunction exhibiting an ohmic-like charge transfer mechanism, driven by the IEF arising from considerable Fermi level differences. The ohmic-like Type-I junction facilitates efficient electron transfer from ZnIn2S4 to FeIn2S4 and preserves the oxidizing holes in ZnIn2S4 for effective scavenger oxidation. This unique feature prevents the inefficient charge separation commonly observed in conventional Type-I heterojunctions. Due to the advantageous ohmic-like electron transfer, an optimized composition of FeIn2S4@ZnIn2S4 with a weight percentage of 10 % FeIn2S4 achieves a notable hydrogen evolution rate of 4.21 mmol g-1h−1, six times higher than isolated ZnIn2S4. Furthermore, the validation of the ohmic-like charge transfer mechanism is supported by theoretical analyses and advanced characterization techniques, including in-situ X-ray photoelectron spectroscopy (XPS), Kelvin probe force microscopy (KPFM), and surface photovoltage (SPV) measurements. This present study introduces a pioneering prototype that shows the successful incorporation of the desired charge transfer pathway in a Type-I heterojunction through the implementation of an IEF regulation strategy.