Quantitative In Situ Monitoring of Cu-Atom Release by Cu2O Nanocatalysts under Photocatalytic CO2 Reduction Conditions: New Insights into the Photocorrosion Mechanism

Abstract

Cu2O is among the most promising photocatalysts for CO2 reduction, however its photocorrosion remains a standalone challenge. Herein, we present an in situ study of the release of Cu ions from Cu2O nanocatalysts under photocatalytic conditions in the presence of HCO3 as a catalytic substrate in H2O. The Cu-oxide nanomaterials were produced by Flame Spray Pyrolysis (FSP) technology. Using Electron Paramagnetic Resonance (EPR) spectroscopy in tandem with analytical Anodic Stripping Voltammetry (ASV), we monitored in situ the Cu2+ atom release from the Cu2O nanoparticles in comparison with CuO nanoparticles under photocatalytic conditions. Our quantitative, kinetic data show that light has detrimental effect on the photocorrosion of Cu2O and ensuing Cu2+ ion release in the H2O solution, up to 15.7% of its mass. EPR reveals that HCO3 acts as a ligand of the Cu2+ ions, promoting the liberation of {HCO3-Cu} complexes in solution from Cu2O, up to 27% of its mass. HCO3 alone exerted a marginal effect. XRD data show that under prolonged irradiation, part of Cu2+ ions can reprecipitate on the Cu2O surface, creating a passivating CuO layer that stabilizes the Cu2O from further photocorrosion. Including isopropanol as a hole scavenger has a drastic effect on the photocorrosion of Cu2O nanoparticles and suppresses the release of Cu2+ ions to the solution. Methodwise, the present data exemplify that EPR and ASV can be useful tools to help quantitatively understand the solid–solution interface photocorrosion phenomena for Cu2O.

Non-graphitized carbon/Cu2O/Cu0 nanohybrids with improved stability and enhanced photocatalytic H2 production

“…Starting from material #Cu1, i.e., D 1 /D 2 (O 2 /CH 4 ):5/0, we have the formation of 92% CuO (JCPDS 48-1548) and 8% Cu 2 O (JCPDS 07-9767). The Cu 2 O-fraction formation is attributed to the slightly anoxic conditions created by the N 2 sheath 16 , 39 , 41 i.e., since D 2 (CH 4 ) = 0 in this case. By changing D 1 /D 2 to a more reducing profile 4/1, see material #Cu2, we have a decrease of CuO phase percentage, favoring the formation of 40% Cu 2 O.…”

“…Photocorrosion can be due to reduction of Cu 2 O to Cu 0 , however it is the oxidation of Cu 2 O to CuO 14 , that is considered as primary source of lattice deterioration i.e. via formation of Cu 2+ -ions 16 . To address photocorrosion, several works discuss the controlled synthesis of stable Cu NPs 17 – 19 based on strategies e.g.…”

“…The above-mentioned FSP set up was based on an FSP reactor enclosed in a glove-box that involved N 2 -gas as reducing agent. Recently, we have presented an alternative FSP configuration 16 , 39 that allows synthesis of reduced metal oxides. This Anoxic-FSP process (A-FSP) has been successfully used to produce highly-photoactive ZrO 2−x 39 , or high purity Cu 2 O nanoparticles 16 .…”

“…Recently, we have presented an alternative FSP configuration 16 , 39 that allows synthesis of reduced metal oxides. This Anoxic-FSP process (A-FSP) has been successfully used to produce highly-photoactive ZrO 2−x 39 , or high purity Cu 2 O nanoparticles 16 . The process is based on incorporation of methane (CH 4 ) as dispersion gas and nitrogen (N 2 ) as sheath gas, in combination with an oxygen-lean atmosphere, allowing the in-situ formation of suboxic metal oxides or pure metallic phases.…”

Flame Spray Pyrolysis Synthesis of Vo-Rich Nano-SrTiO3-x

“…The two A-FSP configurations in Figure 1 A,B are codenamed Radial- and Axial-A-FSP; these define the way in which CH 4 is introduced, respectively. In all cases, the FSP-nozzle was enclosed by a cylindrical metal chamber consisting of two concentric tubes, a sinter metal tube (outer tube) and a perforated metal tube (inner tube) to isolate the flame from the surrounding atmosphere, as has been described in detail in previous works [ 16 , 26 , 27 , 29 ]. The so-produced materials (listed in Table 1 ) are codenamed STO-R and STO-A for Radial- and Axial-A-FSP, respectively.…”