Photoelectrochemical reduction of CO2 using Cu2O
Kelly Mayumi Hirota Barbosa a, Luan Pereira Camargo a, Luiz Henrique Dall´Antonia a
a Universidade Estadual de Londrina, Rodovia Celso Garcia Cid Pr 445 Km380, Londrina, Brazil
Poster, Luiz Henrique Dall´Antonia, 027
Publication date: 7th June 2020

Environmental problems are usually related to the high levels of CO2 in the atmosphere, where anthropogenic actions are the main sources of emissions. In this sense, one of the alternatives to decrease its concentration is the selective conversion of CO2 into higher added value compounds. In the present work, three copper oxide samples with different morphologies were obtained by precipitation synthesis. The samples were deposited on ITO and 304 steel substrates by drop-casting technique to characterize the photoelectrochemical performance. For the physicochemical analysis of the samples the techniques of XRD, SEM, FTIR, diffuse reflectance spectroscopy and textural analysis (BJH) were used. The influence of NH2OH∙HCl on octahedral, spherical and irregular obtained morphology was evaluated, as well as the effect of NaOH on particle size. For octahedral and spherical morphology, only Cu2O were obtained, while for the sample with irregular morphology CuO (9.9%) was detected. The presence of CuO is due to the pH adjustment in the NH2OH∙HCl solution, evidencing a modification of the microstructure and loss of its reducing power. Thus, the presence of Cu+ and Cu2+ ions contributed to the formation of irregular morphology. With the samples deposited in ITO the photoactivity was evaluated, in which all the electrodes presented an excellent performance with visible light (Egap ≈ 2.3 eV). To study the number of layers and photoelectrocatalytic performance, 304 stainless steel was used as substrate. Electrodes with 30 layers showed higher photocurrent and selectivity for CO2 photoelectroreduction. The responses of the three electrodes were related to the specific area of the samples. The irregular morphology presented the largest area (25.04 m2 g-1), followed by the spherical one (15.20 m2 g-1) and with smaller the octahedral morphology (2.049 m2 g-1). The larger specific area allowed a better CO2 adsorption besides the Cu2O/CuO heterojunction which allowed a higher photocurrent (-3.0 mA cm-2 at -0.8 V vs. Ag/AgCl). CO2 photoelectroreduction products after 2 hours (-0.8 V application vs. Ag/AgCl) were evaluated by UV-Vis and HPLC spectroscopy. Using UV-vis spectroscopy, the presence of the band around 300 nm is associated with carbonyl grouping presented in the reduction products. By HPLC, such band was associated with formaldehyde, acetaldehyde and acetone. The octahedral morphology was more selective for formaldehyde formation, while the spherical one for acetaldehyde. For irregular morphology this selectivity was not observed resulting in similar intensity peaks.

The authors thank the Fundação Araucária (PROT. 38.647 SIT.22391), CNPq for financial support and INCT in Bioanalytics (FAPESP grant no. 2014/50867-3 and CNPq grant no. 465389/2014-7) . L.P.C. thanks to CAPES for the Master scholarship. The authors would like also to thank LMEM-UEL, LARX-UEL and LABSPEC-UEL. 

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