Transparent Porous ZnO|Metal Complex Nanostructured Materials: Application to Electrocatalytic CO₂ Reduction

We developed a simple and versatile approach for the electrochemical growth of hybrid ZnO|molecular catalyst nanostructured layers. Metal oxide|catalyst hybrid nanoporous layers with a sponge-like structure at the nanoscale and multiscale three-dimensional (3D) hierarchical structures based on nanoporous zinc oxide (ZnO) layers grown on ZnO nanorods were obtained. The thickness and structure of the hybrid nanoporous layers as well as the catalyst concentration can be tuned. This method allows the introduction of water-soluble molecular catalysts based on porphyrin and/or phthalocyanine derivatives into the ZnO matrix with a homogeneous distribution of the complex into the material. As an illustrative example, combining hybrid ZnO with a very low concentration of an encapsulated Co-based molecular catalyst inside the oxide layer results in a 97% catalytic response toward CO₂ reduction to CO with large currents in an organic solvent, highlighting the excellent electrocatalytic activities of such layers, which combine porosity, electronic conductivity, and synergetic properties from its components.