Hexagonal tungsten oxide nanoflowers as enzymatic mimetics and electrocatalysts

Tungsten oxide (WO_x) has been widely studied for versatile applications based on its photocatalytic, intrinsic catalytic, and electrocatalytic properties. Among the several nanostructures, we focused on the flower-like structures to increase the catalytic efficiency on the interface with both increased substrate interaction capacities due to their large surface area and efficient electron transportation. Therefore, improved WO_x nanoflowers (WONFs) with large surface areas were developed through a simple hydrothermal method using sodium tungstate and hydrogen chloride solution at low temperature, without any additional surfactant, capping agent, or reducing agent. Structural determination and electrochemical analyses revealed that the WONFs have hexagonal Na_0.17WO_3.085·0.17H₂O structure and exhibit peroxidase-like activity, turning from colorless to blue by catalyzing the oxidation of a peroxidase substrate, such as 3,3',5,5'-tetramethylbenzidine, in the presence of H₂O₂. Additionally, a WONF-modified glassy carbon electrode was adopted to monitor the electrocatalytic reduction of H₂O₂. To verify the catalytic efficiency enhancement by the unique shape and structure of the WONFs, they were compared with calcinated WONFs, cesium WO_x nanoparticles, and other peroxidase-like nanomaterials. The results indicated that the WONFs showed a low Michaelis-Menten constant (k_m), high maximal reaction velocity (v_max), and large surface area.