Direct Electrochemical Deposition of Transparent Metal Oxide Thin Films from Polyoxometalates

Abstract

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.

Electrochemical Behaviour of (n‐Bu4N)4[AsVMo11O40] and (n‐Bu4N)4[AsV2Mo10O40] Doped PEDOT Film and Its Quartz Crystal Microbalance Studies

“…Several strategies have been adopted to immobilise the POMs on the surface of the electrode such as drop casting, [11] electrodeposition, [12,13] and entrapment into polymeric matrices, [14,15] layer-by-layer assemblies [16][17][18] and Langmuir À Blodgett films. [19,20] The entrapment into a conducting polymer by use of the electrostatic attraction between POMs (anion) and an oxidized polymer cation is the most common method because of its simplicity, feasibility, room temperature fabrication and adjustable thickness.…”

Nb2O5, LiNbO3, and (Na, K)NbO3 Thin Films from High-Concentration Aqueous Nb-Polyoxometalates

“…32,56 An added challenge of alkali niobates is alkali volatility during annealing and crystallizing at high temperature, and excess alkali is often added to mitigate these problems. 55 Spin-coating 57 and electrodeposition 58 of Nb 2 O 5 from TMA 8−x [H x Nb 6 O 19 ] (x−8) (x = 3) were less challenging in previous studies, and much higher Nb concentration solutions are achievable (1.3 M Nb). 57 However, in our previous study, 57 we found that the deposited Nb 2 O 5 films exhibited poor adhesion due to their tendency to crystallize on the substrate (meaning they crystallize as the TMA−POM salt, leading to poor adhesion upon thermolysis to form Nb 2 O 5 ).…”

Controllable Assembly of MoVI36-Based Polyoxometalate Porous Frameworks with Silver Ions and Lung Cancer Cell-Specific Cytotoxicity

“…Porous POM clusters (ring, wheel, and crown) as inorganic SBUs to construct a POM-based framework endow their integrated pores. As such, POMs, with unmatched physical and chemical properties, are prime candidate SBUs for constructing functional frameworks, covering a wide range of fields among catalysis, luminescence, , medicine, electrochemistry, − and energy storage. − However, the assembly of purely inorganic POM-based porous frameworks provide the possibility of forming new types of porous materials which incorporate the thermodynamic stability of zeolites and mesoporous silicas with the sophistication and versatility of MOFs . Among the various types of POMs, the ring-like {Mo 36 } cluster should be an ideal SBU for the synthesis of various multidimensional frameworks because of its potential 12 growth points.…”