NH2-MIL-125(Ti)/TiO2 nanorod heterojunction photoanodes for efficient photoelectrochemical water splitting

A photoactive amine-functionalized Ti metal-organic framework (MOF) (MIL(125)-NH2(Ti)) layer is uniformly coated on vertically ordered TiO2 nanorods (NRs) via a facile hydrothermal reaction, and the performance of the heterojunction photoanode in photoelectrochemical (PEC) water splitting is studied. The photocurrent density of the MIL(125)-NH2/TiO2 NRs reaches 1.63 mA/cm2 at 1.23 V vs. a reversible hydrogen electrode under AM 1.5 G simulated sunlight illumination, which is ∼2.7 times higher than that of pristine TiO2 NRs. The incident photon-to-electron conversion efficiency of the MIL(125)-NH2/TiO2 NRs improves significantly at λmax = 340 nm, implying the promotion of water oxidation through efficient light absorption and charge separation. The enhancement of the PEC activity in the TiO2 NRs caused by an MIL(125)-NH2 coating is discussed in relation to the surface area and elongated configuration of the TiO2 NRs, the band gap of MIL(125)-NH2(Ti), and the type (II) heterojunction. This study demonstrates the rational design of heterojunctions between the semiconductor and the MOF, which paves the way for new facile and general approaches to achieve a high efficiency in water splitting.