Self-Limiting Adsorption of WO₃ Oligomers on Oxide Substrates in Solution

Abstract

Electrochemical surface science of oxides is an emerging field with expected high impact in developing, for instance, rationally designed catalysts. The aim in such catalysts is to replace noble metals by earth-abundant elements, yet without sacrificing activity. Gaining an atomic-level understanding of such systems hinges on the use of experimental surface characterization techniques such as scanning tunneling microscopy (STM), in which tungsten tips have been the most widely used probes, both in vacuum and under electrochemical conditions. Here, we present an in situ STM study with atomic resolution that shows how tungsten(VI) oxide, spontaneously generated at a W STM tip, forms 1D adsorbates on oxide substrates. By comparing the behavior of rutile TiO2(110) and magnetite Fe3O4(001) in aqueous solution, we hypothesize that, below the point of zero charge of the oxide substrate, electrostatics causes water-soluble WO3 to efficiently adsorb and form linear chains in a self-limiting manner up to submonolayer coverage. The 1D oligomers can be manipulated and nanopatterned in situ with a scanning probe tip. As WO3 spontaneously forms under all conditions of potential and pH at the tungsten–aqueous solution interface, this phenomenon also identifies an important caveat regarding the usability of tungsten tips in electrochemical surface science of oxides and other highly adsorptive materials.

Self-limited growth of an oxyhydroxide phase at the Fe3O4(001) surface in liquid and ambient pressure water

“…The EC-STM data shown here are from an older set of experiments, which are described in detail elsewhere. 22 Briefly, EC-STM measurements were conducted on an Fe 3 O 4 (001) single crystal in 0.1 M NaClO 4 (pH 7), with the EC-STM cell placed in an environmental chamber purged with high-purity Ar. Dissolution of the tungsten tip led to a high coverage of WO x species on the surface after prolonged imaging, which were removed by scanning with high tunnelling current (>2 nA).…”

Copper underpotential deposition on boron nitride nanomesh

“…At potentials above 0.8 V, the formation of this surface oxide is expected to occur, and the presence of Cu 2+ in solution will not preclude this process. The presence of Cu after emersion as detected by XPS can be explained by electrostatic adsorption of Cu 2+ on the partially oxidised Rh substrate [30]. switching of its adhesive properties [15].…”

Wet-Chemically Prepared Porphyrin Layers on Rutile TiO2(110)

“…The procedure we used to clean the TiO 2 (110) single crystals is based on a recipe described by the Diebold group [ 50 ] and is basically a variation of the “Standard Clean 1” (SC-1) cleaning procedure used to clean wafers [ 51 ]: the first step is to sonicate the crystals in 3% soap solution (Labwash premium extra) for 15 min to remove all grease and bigger particles. After sonicating for another 15 min in clean ultrapure water, the crystals are placed in a 65 °C 3:1 mixture of 25% NH 3 and 30% H 2 O 2 for 8 min.…”