Electroreduction of CO2 on Modified Graphene Supported Sn Nanoparticles in Half-Cell and Full Cell Configuration

Abstract

Electrochemical reduction of CO2 is a process that can reduce carbon dioxide from the atmosphere and simultaneously produce useful, value-added chemicals, specifically solar fuel [1]. Depending on the catalyst materials, CO2 can be reduced to single carbon or multi carbon products [2]. Sn nanoparticle was used to catalyze CO2 reduction to produce formate in alkaline medium. Sn nanoparticles were synthesized by the sol-gel method with different precursors at room temperature and supported with carbon black and conductive graphene nano-sheets. Graphene nano-sheets were synthesized by the conventional modified Hammer method [3]. X-ray diffraction (XRD) and transmission electron microscope (TEM) enabled insights into phase formation, shape, and size of the Sn nanoparticles. Reference materials included commercial Sn nanoparticles with carbon support (Sn:C_com), commercial Sn nanoparticles with graphene support (Sn:GN_com), Sn nanoparticle synthesised using Sn (II) 2-ethylhexanoate and Sn (II) chloride as tin precursor with carbon support as respectively (Sn:C_Tin-2-hexa) and (Sn:C_SnCl2). Three-electrode chronoamperometry showed that Sn:GN_com enabled high CO2 electrolysis current density (see Figure 1(a)). Electrochemical impedance spectroscopy (EIS) of the prepared catalysts in CO2-saturated 0.1 M KHCO3 was recorded in a three-electrode rotating disk electrode (RDE) configuration (see Figure 1(b)). The charge-transfer resistance was smallest for Sn:GN_com sample, as well. CO2 reduction was performed in a full electrochemical cell using the same architecture as a low temperature polymer electrolyte fuel cell (PEFC) in alkaline medium with anion exchange membrane. Polarization plots show a unique feature (two different slopes); this change in slope is dominated by a distinct change in the area specific resistance (ASR) value (see Figure 1(c)).In this work, we mainly focus on the CO2 electroreduction to produce formate in a full cell with RDE (rotating disc electrode) measurements providing additional insights into catalytic properties. Our primary goal is to understand the basic underlying physical processes during CO2 reduction in the full cell set up and also find inexpensive and efficient catalytic active materials for the reduction process. Figure 1: CO2 electrolysis (a) and impedance spectra (b) in RDE configuration with different catalyst. (c) Polarisation plots for CO2 reduction in full cell configuration with different flow rate