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

The effective construction of surface catalysts and heterojunctions can accelerate photogenerated carrier separation and transfer to 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 were sequentially loaded onto an α-Fe2O3 photoanode by a strong interaction to form an effective MOF-on-MOF heterojunction, which exhibited excellent PEC catalytic activity and stability. The α-Fe2O3/MIL-96/UiO-66 photoanode exhibited a 125% enhancement of photocurrent density (2.25 mA cm-2) at 1.23 VRHE. The coexistence of Fe3+/Fe2+ and OV could enhance the electrical conductivity and reduce the charge recombination rate of the α-Fe2O3 photoanode. The formation of Fe-O/Fe and weak Fe-Al(MIL-96) and Fe-Zr(UiO-66) coordination facilitated photogenerated electron-hole transport between the α-Fe2O3 photoanode and MIL-96/UiO-66 overlayer. Furthermore, the constructed bimetallic MIL-96/UiO-66 heterojunction synergistically provided more active sites, and promoted photogenerated carrier separation and transfer, thereby reducing the reaction kinetics of water oxidation and enhancing PEC-WS performance. This work provides a new modification route to develop high-efficiency photoelectrode materials with outstanding PEC-WS performance.