Direct Electrochemical Deposition of Transparent Metal Oxide Thin Films from Polyoxometalates

Transition metal oxide coatings, owing to their unique combination of optoelectronic, electrochemical, and chemical properties, are at the forefront of functional thin films across diverse technologies. However, achieving uniform and conformal metal oxide thin films of precise nanoscale thickness and optical quality is largely limited to atomic layer deposition methods. Here, we report a direct, fast, solution-based, ambient-condition electrochemical method to deposit transparent thin films of amorphous niobium oxide and tantalum oxide from polyoxometalate precursors dissolved in aqueous electrolytes. The acid-catalyzed condensation of the polyoxometalates is driven by the potentiostatic oxidation of water at the surface of the transparent working electrode. Film thickness can be tuned at the nanoscale by varying the applied potential. We deposited niobium oxide and tantalum oxide conformally on mesoporous nanocrystal films to demonstrate the abilities of this electrochemical method as an alternative approach to fabricate optical quality composites. These composites exhibit electrochromic and antiphotochromic performance comparable to that of the equivalent composites fabricated by established conventional methods such as atomic layer deposition.