Electrochemical Reduction CO₂ to Formate on Sno/Gdl Electrode

Abstract

The CO 2 conversion using electrochemical method is an attractive proposition due to its several advantages such as the controllable electrode potentials, reaction temperature and the recycled supporting electrolytes. 1 To date, formic acid, carbon monoxide, methanol, and oxalic acid have been prepared by this way. However, the key technological challenge for electrochemical reduction of CO 2 is the preparation of the electrode with high catalytic activity, high selectivity and long term stability. Considering these difficulties, developing new material synthesis technology to give innovative new catalysts with optimal performance is the priority. Tin (Sn) and copper (Cu) are considered as promising electrocatalysts to convert carbon dioxide (CO 2 ) to fuels (e.g. formate, methanol or hydrocarbons) because of their low cost, easy availability and reasonable overall Faradaic efficiency towards fuel production. 2 However, the deactivation of Sn metal electrodes during CO 2 reduction is very fast, and requires at least 0.86 V of overpotential to attain a CO 2 reduction partial current density of 4−5 mAcm -2 in an aqueous solution saturated with 1 atm CO 2 . 3 Combined with the advantages of metal tin, we here report a simple one-step hydrothermal synthesis of SnO nanocatalyst with good electrochemical performance of high catalytic activity and high selectivity. The crystalline SnO nanocatalyst were prepared using a simple hydrothermal method as follows: 2 mmol Tin (Ⅱ) Chloride dehydrates, 12 mmol carbamide and 0.2g PVP were dissolved into 50mL deionized water under vigorous stirring to form a homogeneous solution. Then the mixture was transferred into a 100 mL stainless-steel autoclave and heated at 140,160,180,200 o C for 12 h, respectively. Then the precipitate was collected by centrifugation, washed with deionized water and absolute ethanol for several times, until the pH was neutral, finally dried at oven at 85 o C for 12h. The crystal structure of the product was characterized by XRD and SEM. The catalyst electrode was prepared by SnO powder bonded with Nafion solution and isopropanol, and spread over the gas diffusion layer (GDL). The catalytic activity of SnO nanocatlyst supported on GDL as the cathode electrode was measured using cyclic voltammetry (CV) and linear sweep voltammetry (LSV) in 0.5M KHCO 3 aqueous solution saturated with both N 2 and CO 2 , respectively. Figure 1 shows the CV curves on the SnO/GDL electrode. It can be seen that the anodic peaks between -0.75V~ -0.25V and the cathodic peak between -0.55V~ -0.9V. The onset potential in 0.5M KHCO 3 solution saturated with CO 2 was found to be at -0.554 V, which is 12 mV more positive than that under N 2 (-0.673V). At an potential of -1.6V, the current density in CO 2 -saturated 0.5M KHCO 3 reached 17.1 mAcm -2 which is nearly 4 times higher than that under N 2 (Fig. 1). All the above reults indicates that participation of CO 2 reduction contributes to the enhancement of cathodic current. References 1. J. L. Qiao, Y. Y. Liu, Y. Y, F. Hong, J. J. Zhang. Chem. Soc. Rev., 43 , 631 (2014 ). 2. J.J.Wu, F.G. Risalvato, S. G.Ma, X.-D. Zhou. J. Mater. Chem. A , 2 , 1647 (2014). 3.Y.Hori, H.Wakebe, T.Tsukamoto, O.Koga, Electrochim. Acta , 39 , 1833 ( 1994). Figure 1