Fabrication Of Porous Tin And Its Application To Electrochemical Reduction Of CO₂

As a mild and efficient method of CO2conversion, CO2electroreduction has awide application prospect. It also provides an effective method for the storage ofintermittent energy sources such as solar energy, wind energy, tidal power and so on.Metals with high hydrogen evolution overpotential (In, Sn, Pb and Hg) have highselectivity to CO2electroreduction to HCOOH. Sn is an ideal cathode material amongthese metals because it is nontoxic, and cheap. Hydrogen bubble dynamic templatesare a new green method to prepare porous metal material because that method is lowcost, easy of operation and without removal of the template agent. This porousmaterial has good gas liquid channel, high electrochemical surface area and favorableroughness. Therefore, this is a potential method to prepare an ideal cathode for CO2electroreduction.The porous Sn electrode was fabricated by hydrogen bubble dynamic templatesusing Cu as substrate. Effects of electrodeposition parameters on the morphology andpolarization curves of Sn electrode were investigated. Suitable electrodepositionparameters were determined: electrolyte consisted of1.2M HCl,0.01M SnCl2and0.01M sodium citrate;4A·cm-2deposition current density; and1min deposition timein ice-water bath. The as-prepared porous Sn electrode was characterized by SEM,EDS, XRD and cyclic voltammetry(CV) SEM images indicated that a kind ofself-assembly honeycomb-like Sn porous network, and EDS resulted that there wereno impurities. XRD revealed that there was Sn-Cu intermetallic compound layer at theinterface between tin deposit layer and copper, which can enhance the bonding forceof the two. The electroactive surface area of the porous Sn electrode was derived fromCV curves at different scan rates, and it was six times higher than that of the Sn plate.The porous Sn electrode was applied in CO2electroreduction to formic acid. TheCV of the Sn plate electrode and the porous Sn electrode were compared, it wasdemonstrated that the current density of CO2electroreduction increased on the porousSn electrode and a more positive onset potential apperaed. Effects of concentration ofKHCO3, potential and temperature were investigated. The results indicated the bestcatalytic activity can be obtained at-1.7V vs. SCE in0.5M KHCO3electrolyte at5℃,with73.9%current efficiency of formic acid. Tafel experiments were conducted on both the porous Sn electrode and the Sn plate electrode, which revealed that therate-determining step was same on both electrodes, which was one initial electrontransfer to CO2to form a surface adsorbed·CO2ads-. The results of electrochemicalimpedance spectra from CO2electroreduction on the porous Sn electrode indicatedthat electrchemical impedance spectra included three parts: high frequency Warburgcontrolled area, middle frequency capacitive loop of faraday resistance and lowfrequency capacitive loop of diffusion of adsorbed speciese. Finally, investigationg ofreusability resulted that the eletrocatalytic performance of the porous Sn electrodedecreased, and it maybe caused by deposits loss.