Abundant Surface Defects in Cobalt Hydroxides/Oxyhydroxides Induced by Zinc Species Facilitate Water Oxidation.

The complex process of the anodic oxygen evolution reaction (OER) severely hinders overall water splitting, which further limits the large-scale production and application of hydrogen energy. In this work, one type of bimetallic coordination polymer of ZnCoBTC using the MOF-on-MOF strategy has been synthesized where both Co(II) and Zn(II) cations exhibit the same coordination environment. By applying an electric potential, the predesigned bimetallic MOF precursor can be conveniently degraded into CoOxHy as an active species for efficient OER. Owing to the dissolution of ZnOxHy species, in situ formed disordered defects on the external surface of the catalyst increase the specific surface area as well as expose abundant active materials. Therefore, the ZnCoOxHy nanosheet shows excellent OER performance and reaches an overpotential of only 334 mV at 10 mA cm-2 with a Tafel slope of 66.4 mV dec-1, indicating fast reaction kinetics. The results demonstrate that metals with the same coordination environment can undergo in situ replacement or secondary growth on the pristine MOF, and they can be electrochemically degraded into highly efficient catalysts for future energy applications.

MOF-on-MOF-Derived Hollow Co3 O4 /In2 O3 Nanostructure for Efficient Photocatalytic CO2 Reduction.

The photocatalytic transformation of carbon dioxide (CO2 ) into carbon-based fuels or chemicals using sustainable solar energy is considered an ideal strategy for simultaneously alleviating the energy shortage and environmental crises. However, owing to the low energy utilization of sunlight and inferior catalytic activity, the conversion efficiency of CO2 photoreduction is far from satisfactory. In this study, a MOF-derived hollow bimetallic oxide nanomaterial is prepared for the efficient photoreduction of CO2 . First, a unique ZIF-67-on-InOF-1 heterostructure is successfully obtained by growing a secondary Co-based ZIF-67 onto the initial InOF-1 nanorods. The corresponding hollow counterpart has a larger specific surface area after acid etching, and the oxidized bimetallic H-Co3 O4 /In2 O3 material exhibits abundant heterogeneous interfaces that expose more active sites. The energy band structure of H-Co3 O4 /In2 O3 corresponds well with the photosensitizer of [Ru(bpy)3 ]Cl2 , which results in a high CO yield of 4828 ± 570 µmol h-1  g-1 and stable activity over a consecutive of six runs, demonstrating adequate photocatalytic performance. This study demonstrates that the rational design of MOF-on-MOF heterostructures can completely exploit the synergistic effects between different components, which may be extended to other MOF-derived nanomaterials as promising catalysts for practical energy conversion and storage.