Photocatalytic and Electrocatalytic Properties of Cu-Loaded ZIF-67-Derivatized Bean Sprout-Like Co-TiO₂/Ti...

ZIF-derivatized catalysts have shown high potential in catalysis. Herein, bean sprout-like Co-TiO₂/Ti nanostructures were first synthesized by thermal treatment at 800 °C under Ar-flow conditions using sacrificial ZIF-67 templated on Ti sheets. It was observed that ZIF-67 on Ti sheets started to thermally decompose at around 350 °C and was converted to the cubic phase Co₃O₄. The head of the bean sprout structure was observed to be Co₃O₄, while the stem showed a crystal structure of rutile TiO₂ grown from the metallic Ti support. Cu sputter-deposited Co-TiO₂/Ti nanostructures were also prepared for photocatalytic and electrocatalytic CO₂ reduction performances, as well as electrochemical oxygen reaction (OER). Gas chromatography results after photocatalytic CO₂ reduction showed that CH₃OH, CO and CH₄ were produced as major products with the highest MeOH selectivity of 64% and minor C₂ compounds of C₂H₂, C₂H₄ and C₂H₆. For electrocatalytic CO₂ reduction, CO, CH₄ and C₂H₄ were meaningfully detected, but H₂ was dominantly produced. The amounts were observed to be dependent on the Cu deposition amount. Electrochemical OER performances in 0.1 M KOH electrolyte exhibited onset overpotentials of 330-430 mV (vs. RHE) and Tafel slopes of 117-134 mV/dec that were dependent on Cu-loading thickness. The present unique results provide useful information for synthesis of bean sprout-like Co-TiO₂/Ti hybrid nanostructures and their applications to CO₂ reduction and electrochemical water splitting in energy and environmental fields.