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Metal organic frameworks (MOFs) have emerged as a novel template to develop porous photocatalytic materials for solar fuel conversion. In this work, we report the synthesis, charge separation dynamics, and photocatalytic performance of the TiO 2 /CuO heterostructure derived from mixed-phase MOFs based on Ti and Cu metal nodes, which demonstrates significantly enhanced catalytic activity for the hydrogen evolution reaction (HER) compared to metal oxides derived from single node MOFs. More importantly, using transient absorption spectroscopy, we identified the specific role each component in the heterostructure plays and unravelled the key intermediate species that is responsible for the exceptional photocatalytic activity of the heterostructure. We found that the HER is initiated with ultrafast electron transfer (<150 fs) from the molecular photosensitizer to the conduction band of TiO 2 , where TiO 2 acts as an electron mediator and shuttles the electron to the CuO cocatalyst, facilitating charge separation and ultimately boosting the HER efficiency. These results not only demonstrate the great potential of using mixed-phase MOFs as templates to synthesize mesoporous heterostructure photocatalysts but also provide important insight into the HER mechanism. 

Controlling the 3-D morphology of nanocatalysts is one of the underexplored but important approaches for improving the sluggish kinetics of the oxygen evolution reaction (OER) in water electrolysis. This work reports a scalable, oil-based method based on thermal decomposition of organometallic complexes to yield highly uniform Ni–Fe-based nanocatalysts with a well-defined morphology ( i.e. Ni–Fe core–shell, Ni/Fe alloy, and Fe–Ni core–shell). Transmission electron microscopy reveals their morphology and composition to be NiO x –FeO x /NiO x core-mixed shell, NiO x /FeO x alloy, and FeO x –NiO x core–shell. X-ray techniques resolve the electronic structures of the bulk and are supported by electron energy loss spectroscopy analysis of individual nanoparticles. These results suggest that the crystal structure of Ni is most likely to contain α-Ni(OH) 2 and that the chemical environment of Fe is variable, depending on the morphology of the nanoparticle. The Ni diffusion from the amorphous Ni-based core to the iron oxide shell makes the NiO x –NiO x /FeO x core-mixed shell structure the most active and the most stable nanocatalyst, which outperforms the comparison NiO x /FeO x alloy nanoparticles expected to be active for the OER. This study suggests that the chemical environment of the mixed NiO x /FeO x alloy composition is important to achieve high electrocatalytic activity for the OER and that the 3-D morphology plays a key role in the optimization of the electrocatalytic activity and stability of the nanocatalyst for the OER.