Physical Chemistry seminar — Wei-Jyun Wang
About the event
Title: Electrochemical Oxidation of Formate and Reduction of CO2 into Formate and C2 Compound
Abstract: The consumption of fossil fuel since the industrial revolution in 1760s releases massive amount of CO2 into the atmosphere. The rising atmospheric CO2 concentration has been correlated to global warming and occurrences of unprecedented extreme weather events. In order to ensure the sustainability of human civilization, it is imperative to finding a renewable fuel to reduce the usage of fossil fuel. Formate (HCOO-) is considered as one of the promising alternative energy carriers, which can be fed into a direct formate fuel cell (DFFC) to generate electricity via the formate oxidation reaction (FOR). Moreover, HCOO- can be produced via the electrochemical reduction of CO2 (eCO2R). This provides opportunity to develop a sustainable regenerative energy system by combining an eCO2R unit and a DFFC, which can produce electricity without creating CO2 emission. In addition, formate can be also fed into an electrochemical reforming reactor to produce hydrogen via (FOR), which may be used to reduce the cost of hydrogen economy since HCOO- exists in the liquid state so that it does not require expensive pressurized tanks to transport and store HCOO-. Palladium (Pd) is one of the few electrocatalyst that can be used for both of FOR and the eCO2R into formate (eCO2RF) at low overpotential. However, the low catalytic activity and the high material cost of Pd prohibit its application as the electrocatalyst at the industrial scale. Another way to control CO2 emission is to reuse CO2 to produce valuable C2 compounds which are conventionally produced via energy intensive processes, such as ethylene. Copper (Cu) has currently received most of the attention for its application as the electrocatalyst used to convert CO2 into C2 compounds. Yet, the eCO2R into C2 compounds (eCO2C2) on the surface of different metals with different amount of surface energy has not yet been studied.
The goal of this research is to improve the catalytic activity of Pd toward FOR and eCO2RF by changing its electronic properties via synthesizing bimetallic Pd-based catalysts. Carbon supported CuPd (CuPd/C) and iron@iron oxide supported Pd nanoparticles (Fe@FeOx/Pd NPs) were synthesized via the adsorbate induced surface segregation and the successive salt reduction, respectively. TEM, XRD, and XPS were used to characterize the physical and electronic properties of the catalysts. Cyclic voltammetry and chronoamperometry were used to characterize the chemical properties of the catalysts. NMR and the gas chromatography was used to quantify the amount of formate and C2 compounds produced by eCO2R, respectively. The upshift of the d-band center and higher electrochemical activity of CuPd/C and Fe@FeOx/Pd catalyst compared to monometallic Pd/C NPs and Pd NPs were detected, which indicate the lowering of the bonding strength of key adsorbate species for FOR, eCO2F, and eCO2RE on the surface of the bimetallic catalysts may results in the improvement the bimetallic catalysts toward FOR, eCO2F, and eCO2RE. eCO2C2 on the surface of aluminum (Al), Fe, Cu, and titanium (Ti) was studied and the effect of the surface energy on the catalytic activity toward eCO2C2 is investigated.