Facile and scalable synthesis of Cu2O-SnO2 catalyst for the photoelectrochemical CO2 conversion
Creators: name: Zoli, Maddalena
name: Roldán, Daniela
name: Guzmán, Hilmar
name: Hernández, Simelys
name: Chiodoni, Angelica
name: Bejtka, Katarzyna
name: Russo, Nunzio
Publisher: name: Zenodo
Year: 2021
Subjects: Cu2O-SnO2 catalyst
photoelectrochemical CO2 conversion

description: The conversion of the atmospheric CO<sub>2</sub> to value-added compounds is more and more attractive to the scientific community, since natural sink cannot keep up with the constant anthropogenic emission and amplification processes. Recently, CO<sub>2</sub> concentration in the atmosphere exceeds 410 ppm, and its growth has remained constant since the 50s<sup>[1]</sup>. Renewable and green approaches to CO<sub>2</sub> recovery are aimed to minimize the worrying impact of its emission to the environment, and to drive the transition to a new circular economy approach in chemistry and energy production. Within the depicted scenario, electrochemical and photoelectrochemical CO<sub>2</sub> reduction are being widely investigated as promising methods to transform CO<sub>2</sub>, under mild reaction conditions, into useful chemicals or fuels. For instance, alcohols, CO and HCOOH that can be exploited as renewable energy sources or as key intermediates for the chemical industry. Among the non-precious metal oxides, Cu<sub>2</sub>O is a cheap, abundant and intrinsically p-type semiconductor. Due to its narrow band gap (~ 2 eV) and the suitable positioning of conduction and valence bands, Cu<sub>2</sub>O is an ideal photocatalyst for CO<sub>2</sub>RR. Simultaneously, SnO<sub>2</sub> is an n-type direct band-gap semiconductor with noticeable electron mobility together with an intrinsic stability. It openly transpires the dual role of Cu<sub>2</sub>O, as photoabsorber and forming a p-n junction with Tin Oxide. In this work, the synthesis of photoactive copper-tin-oxide-based catalyst was optimized by a co-precipitation method<sup>[2]</sup>, employing Cu(NO<sub>3</sub>)<sub>2</sub>·3H<sub>2</sub>O and SnCl<sub>4</sub>∙5H<sub>2</sub>O into a stirred and heated reactor. A solution of Na<sub>2</sub>CO<sub>3</sub> was added as a precipitant agent, while NaBH<sub>4 </sub>as the reducing one<sup>[3]</sup>, in order to promote the Cu<sub>2</sub>O formation. The work-up protocol, based on copious MilliQ water washings, was implemented and finally optimized.[SH1] The characterization step included Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Analysis (EDX) X-rays Diffraction Analysis(XRD), UV-Visible [SH2] Spectroscopy analysis, among others, and allowed the morphological assessment, the porosity value estimation and the crystalline phase evaluation. With the latter, it has been found a correspondence to the cubic crystalline phase (cuprite) of Cu<sub>2</sub>O and consequently confirmation that the reduction process has been successfully carried out. The so obtained catalyst was then deposited it onto a GDL (Gas Diffusion Layer) and FTO-based substrates by spray coating of an ink containing: the catalysts, Vulcan carbon (to increase the electrode conductivity), Nafion as binder and Isopropanol as carrier. The photo-electrochemical activity for the CO<sub>2</sub> reduction reaction was tested in the dark and under sunlight simulated conditions by means of Linear Sweep Voltammetry (LSV) and Chrono-Potentiometry (CP) analyses. Relevant current density (<em>j</em>) values of up to 40 mA/cm<sup>2</sup> were observed, and from the products analysis during the CP a high Faradaic Efficiency to CO was obtained. The influence of the ink composition was accurately investigated in terms of interaction among all the components and with respect to the employed substrate, taking into account sun-light activity and stability of the prepared electrodes towards their future utilization in a device for the sun-driven CO<sub>2</sub> conversion to high-added value products.