Reduction of  CO 2 on Fluorine‐Doped SnO2 Thin‐Film Electrodes

Abstract

The reduction process of fluorine-doped SnO~ (SnQ:F) electrode in the presence of CO2 was investigated by x-ray diffraction, x-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), colorimetry, and gas chromatography. It has been found that a SnQ:F with (200) preferred orientation undergoes the following five reduction stages:i. Oxygen-defect formation and constant hydrogen evolution.2. Acceleration of oxygen-defect formation and hydrogen evolution. At this stage, formyl -HCO-and methoxy -CH30are formed on the surface.3. Dissolution of (200) surface and exposure of (Ii0) surface. Dissolution of SnO2:F accompanies CO evolution. The CO formation rate increases, and H2 formation rate decreases as the reduction proceeds.4. Electrodeposition of dissolved Sn on an exposed (ii0) surface. The CO formation rate decreases and finally stops as the deposition proceeds.5. The surface is covered with elemental Sn, and the oxide electrode acts as a metal electrode. Cyclic voltammetry cycled between -0.i V and -1.4 V vs. SCE showed nearly the same current-voltage characteristics for SnO2 and Sn electrodes in a CO2 saturated solution, implying that a tin metal is oxidized by CO2 at less cathodic potentials (>-0.5 V vs. SCE).The electrolytic reduction of carbon dioxide semiconductor electrode was investigated in order to clarify the fixation mechanism of CO2. It is well known that the reduction products critically depend on the electrode used. 1-7 For example, formic acid, carbon monoxide, and methane are preferentially produced on Sn electrode, Au electrode, and Cu electrode, respectively. The reason why such differences arise remains unknown. It is natural to consider that CH3OH can originate from hydrogenation of COad and CH4, from dissociation of COad to Cad and Oad. Thus CH3OH and CH4 formation are differentiated on the basis of the electrode's ability to split CO, controlled by the affinity of the electrode for Oad.A metal usually forms an oxide and a sulfide such as SnO2 and SnS, which are semiconductors. Metal oxide and metal sulfide are likely to be reduced to metals with cathodic biases because they are "oxidized forms" of metals. Therefore, the detection and identification of reduction products on oxides and sulfides will give clues to clarify the fixation mechanism. However, use of the oxidized materials makes the system more complicated because the additional reduction process, that we will call electrode corrosion, is added to it. Moreover, the surface properties of the electrode can be changed drastically due to the progress of the electrode reaction. This means that the reduction products can be different as the electrode corrosion progresses.For this problem, we applied the XPS and colorimetric measurements as well as the conventional analysis with a gas chromatograph. This is a first report of a series of measurements on metal oxides.

Stability limits of tin-based electrocatalyst supports

“…In this way less stable oxides are avoided, improving the overall stability of the material. Nevertheless, electrodeposition at very low potentials as well as CO 2 reduction 35 will lead to dissolution of Sn from FTO. Moreover, in chloride containing electrolytes stability of FTO can be an issue 37, 38 .…”

“…Thus, ITO and FTO were studied in a comprehensive overview of substrate materials for electrochemical applications, in which a broader stability of FTO was claimed 25 . Most of the results on stability originate from pre- and post-measurements of the oxides resistivity, capacitance, optical properties, and surface composition 1, 3, 15, 16, 26–35 . Only in a few works dissolution was actually estimated, e.g.…”

Structural and electronic evolution in the Cu3SbS4–Cu3SnS4solid solution

“…The binding energy of Sb 3d and Sn 3d are consistent with Sb and Sn in predominantly 5+ and 4+ oxidation states, respectively. 32,35,36 However, while the Sb 3d XPS data show predominantly Sb in the 5+ oxidation state, the presence of a small amount of Sb 3+ would be almost indiscernible, since the binding energies of the 3d electrons on the +5 and +3 oxidation states are separated by only about 3 eV. 37,38 Fig .…”

Extended visible photosensitivity of carboxyethyltin functionalized polyoxometalates with common organic dyes enabling enhanced photoelectric performance

“…44 The two peaks at 494.5 and 486.1 eV were consistent with the XPS spectrum of Sn 3d. 45,46 The above results suggested that SnR-Co-P 2 W 15 in the lm exists in its oxidized form. The binding energy located at 530.3 and 531.9 eV in Fig.…”