Synergetic catalytic behavior of dual metal-organic framework coated hematite photoanode for photoelectrochemical water splitting performance

The performance of oxide photoanodes constructed with hematite (Fe₂O₃) nanostructures is among the best for low-cost photoelectrochemical water-splitting cells. However, due to limited light absorption capacity, a high photogenerated charge carrier recombination rate, and sluggish surface oxygen evolution reaction (OER) kinetic on the surface, the photocurrent density generated by bare hematite is lower than the theoretical value. To overcome these limitations, we fabricate hematite photoanodes with a dual metal–organic framework (MIL-88B@ZIF-67) coating, which greatly enhances light harvesting efficiency and the intrinsic charge carrier transport rate. Owing to these spectacular advantages, the optimized Fe₂O₃/MIL-88B@ZIF-67 photoanode affords a stable photocurrent density of 2.52 mA∙cm⁻² at 1.23 V vs. a reversible hydrogen electrode (RHE) under one sun irradiation. The photocurrent density is significantly higher than that achieved with a bare Fe₂O₃ photoanode (0.27 mA∙cm⁻²). Most importantly, the cathodic shift of the Fe₂O₃/MIL-88B@ZIF-67 photoanode (119 mV) is larger than that of pristine Fe₂O₃. The measured incident photon-to-electron conversion efficiency of the Fe₂O₃/MIL-88B@ZIF-67 photoanode reaches 30.85% at 330 nm. A photocurrent decay of only 5% over 20 h indicates that the photoanode is also extraordinarily stable. We find that it is crucial to precisely control the number of MIL-88B@ZIF-67 coating layers to reduce the charge carrier recombination rate. We expect that our approach will be effective for the design of efficient and stable photoanodes for PEC water splitting.