Constructing MOF-on-MOF heterojunction on hematite photoanode for efficient photogenerated carrier transport

The effective construction of surface catalyst and heterojunction can accelerate photogenerated carrier separation and transfer to further improve photoelectrochemical water splitting (PEC-WS) performance. Integration of two or more metal-organic frameworks (MOFs) as surface overlayers onto photoelectrode materials can build a nanoscale MOF-on-MOF heterojunction to drive the separation and transfer of photogenerated electron-hole pairs. In this work, MIL-96 and UiO-66 MOFs are sequentially loaded onto α-Fe₂O₃ photoanode by a strong interaction to form an effective MOF-on-MOF heterojunction, which exhibits excellent PEC catalytic activity and stability. The α-Fe₂O₃/MIL-96/UiO-66 photoanode exhibits a 125% enhancement of photocurrent density (2.25 mA/cm²) at 1.23 V_RHE. The coexistence of Fe³⁺/Fe²⁺ and O_V can enhance the electric conductivity and reduce charge recombination rate of α-Fe₂O₃ photoanode. The formation of Fe-O/Fe and weak Fe-Al(MIL-96) and Fe-Zr(UiO-66) coordination facilitates photogenerated electron-hole transport between α-Fe₂O₃ photoanode and MIL-96/UiO-66 overlayer. Furthermore, the constructed bimetallic MIL-96/UiO-66 heterojunction synergistically provides more active sites, and promotes photogenerated carrier separation and transfer, finally effectively reducing the reaction kinetics of water oxidation and enhancing the PEC-WS performance. This work provides a new modifying route to develop the high-efficiency photoelectrode materials with outstanding PEC-WS performance.