Contribution of CuxO distribution, shape and ratio on TiO2 nanotubes to improve methanol production from CO2 photoelectroreduction

Abstract

Many studies are focused on the development of materials for converting carbon dioxide into multicarbon oxygenates such as methanol and ethanol, because of their higher energy density and wider applicability. In this work, TiO 2 nanotubes (NT/TiO 2 ) were modified with Cu x O nanoparticles in order to investigate the contribution of different ratio of Cu 2 O/CuO and its distribution over NT/TiO 2 for CO 2 photoelectro-conversion to methanol. The photoelectrodes were built by anodization process to obtain NT/TiO 2 layer, and the decoration with Cu x O hybrid system was carried out by electrodeposition process, using Na 2 SO 4 or acid lactic as electrolyte, followed by annealing at different temperatures. X-ray photoelectron spectroscopy analysis revealed the predominance of Cu +1 and Cu +2 at 150°C and 300°C, respectively. X-ray diffraction and scanning electron microscopy indicated that under lactic acid solution, the oxide nanoparticles exhibited small size, cubic shape, and uniform distribution on the nanotube wall. While under Na 2 SO 4 electrolyte, large nanoparticles with two different morphologies, octahedral and cubic shapes, were deposited on the top of the nanotubes. All modified electrodes converted CO 2 in methanol in different quantities, identified by gas chromatograph. However, the NT/TiO 2 modified with CuO/Cu 2 O (80:20) nanoparticles using lactic acid as electrolyte showed better performance in the CO 2 reduction to methanol (0.11 mmol L −1 ) in relation to the other electrodes. In all cases, a blend among the structures and nanoparticle morphologies were achieved and essential to create new site of reactions what improved the use of light irradiation, minimization of charge recombination rate and promoted high selectivity of products.Keywords CO 2 photoelectroreduction . Hybrid TiO 2 -Cu x O photocatalysts . p-n heterojunction . Electrolyte design . Methanol formation

Heterostructure Cu2O@TiO2Nanotube Array Coated Titanium Anode for Efficient Photoelectrocatalytic Oxidation of As(III) in Aqueous Solution

“…Two main peaks with binding energies of 932.5 and 952.3 eV were observed (Figure b), corresponding to Cu 2p 3/2 and Cu 2p 1/2 , respectively. These peaks were further deconvoluted into four peaks, at 932.5 and 952.3 eV corresponding to the presence of Cu 2 O and at 934.6 and 954.2 eV corresponding to Cu 2+ . − XPS measurements could only detect the shallow surface element composition; thus, the emergence of Cu 2+ could result in a small part of Cu 2 O nanoparticles being oxidized during the sample drying and treatment under the normal ambient condition, which had been revealed by many previous studies for the preparation of Cu 2 O nanoparticles . The curve-fitted Ti 2p high-resolution spectrum (Figure c) exhibited two peak components centered at 458.5 and 464.3 eV which were ascribed to Ti 2p 1/2 and Ti 2p 3/2 , respectively.…”

Reduction of CO2 by Photoelectrochemical Process Using Non‐Oxide Two‐Dimensional Nanomaterials – A Review

“…Other studies in the literature also report the preliminary generation of CO from the reduction of CO 2 , followed by the formation of other products (CO route). [9,143] In same work, Wang et al demonstrated that the union of ZnTe and g-C 3 N 4 stabilizes both CO 2 (Figure 8a) and CO (Figure 8b) adsorption species. The DFT study indicated that CO 2 is adsorbed preferentially on ZnTe, favoring the conversion of CO 2 into CO.…”

“…À ; while at pH 10 the concentration of both species are practically the same; and, at pH 11 CO 3 À 2 species are predominant. [31] At electrolytes based on bicarbonates (NaHCO 3 and KHCO 3 ) that are very commonly used for CO 2 reduction, [9,[32][33][34][35][36] the hydroxyl groups occurrence is minimized at moderated pH like pH 8, once the HCO 3…”

“…[1,25,39] This reduction process is a multi-electron stepwise phenomenon involving different surface-bound species with different reactivity, which culminate in a number of possible carbon products, from 1C to 3C molecules, such as carbon monoxide, formaldehyde, methane, methanol, ethanol, acetone and so on. [9,33,40] (Table 1) These products may be generated from different intermediates according to the consumption of different numbers of electrons and protons, consequently, using different routes of production. Some of the possible routes for the main products obtained from 2D non-oxide materials cited in this chapter can be seen in Figure 3.…”

“…[2] Not differently from usual photocatalysts, to develop an efficient 2D catalyst for application in solar-driven energy conversion and storage, there is a necessity of optimize the electronic structure and aligning the position of the bands of the semiconductor due to their strong dependence to the charge transfer process. [3] Figure 1b illustrates some of the possible options for surface engineering considering photocatalysts based on 2D materials, including strategies to (i) employ doping of the catalyst, which can modify its surface and/or bulk, [7] (ii) control the interlayer architectonics, which can increase the interlayer spacing enabling a better accommodation of foreign ions and improving diffusion kinetics, [8] (iii) expose an active facet, [9,10] (iv) control the morphology of the catalyst through properties such as thickness and particle size, [11] (v) control the defects in the catalyst surface, such as oxygen vacancies or corners and edges of the catalyst particles, [12,13] (vi) join different catalysts together to form heterojunctions. [14,15] Moreover, among 2D materials there are the so called ultrathin 2D nanostructures that represent an emerging group of nanomaterials that have sheet-like structures with large lateral size, reaching usually several hundred nanometers, and, thickness of only a few atoms which usually have less than 5 nm.…”