Electrochemical Quartz Crystal Microbalance Studies of Electron Addition at Nanocrystalline Tin Oxide/Water and Zinc Oxide/Water Interfaces:  Evidence for Band-Edge-Determining Proton Uptake

Abstract

Electrochemical quartz crystal microbalance (EQCM) measurements provide compelling evidence for chargecompensating cation uptake by nanocrystalline SnO 2 and ZnO electrodes during electron addition. Comparative light water/heavy water measurements establish that the adsorbed or intercalated ions are protons or deuterons. Additional studies as a function of pH implicate water, rather than hydronium ions, as the proton source. The new results, when combined with previous results for titanium dioxide in nonaqueous electrolytes, suggest that charge-compensating cation intercalation is a general mode of reactivity for metal oxide semiconductors. Finally, the new observations raise significant fundamental questions concerning (1) chemical control of band energetics, (2) possible band-edge-unpinning phenomena, and (3) relationships between band edge energies and driving forces for isolated electron transfer reactions.

Electron trapping induced electrostatic adsorption of cations: a general factor leading to photoactivity decay of nanostructured TiO2

“…Moreover, it has long been realized that electron trapping in band gap states can induce proton (or other cation ions) charge compensation uptake (call ETPU). 28 Herein, we propose and further verify for the first time that it is the ETPU process that leads to the general and continuous photocurrent decay.…”

“…Moreover, proton charge compensation uptake is also common for many other metal oxides. 28 The above factors make us further propose that the negative influence of ETPU on photoactivity should be general in various non-TiO 2 PEC systems, which needs to be confirmed with more experimental evidences.…”

Electron Injection, Recombination, and Halide Oxidation Dynamics at Dye-Sensitized Metal Oxide Interfaces

“…5 Insulating ZrO 2 films were prepared from Zr(i-OPr) 4 in a similar fashion. 6 Transparent SnO 2 films were prepared using a slight modification of a published procedure: 7 One drop of Triton X-100 surfactant was added to 1 mL of 15% SnO 2 colloidal solution (Alfa). This mixture was deposited on the substrate and spread with a glass rod over an area masked with Scotch tape.…”

Modified TiO2coatings for cathodic protection applications

“…Such an electron transfer leads to reduction of Sn 4C and charge storage is rendered possible via cation intercalation. Cation intercalation in SnO 2 has been well proven in the literature [11,12]. A possible mechanism would be as given below…”