Mixed Metal Ni(M)/YSZ for High-Temperature CO2 Electroreduction to CO

Abstract

Electroreduction of CO2 to fuels using renewable energy can significantly help in reducing emissions and dependence on fossil fuels. Electrochemical reduction of CO2 to hydrocarbon fuels (CHx) is energy inefficient owing to the multistep-multielectron transfer process, which possesses many kinetic limitations. The selective conversion of CO2 to CO is energy efficient. CO as product can be directly used as a fuel or converted to hydrocarbon fuels by using green hydrogen via Fischer-Tropsch reactions. We have used Ni(M)x/YSZ based electrodes to study electroreduction of CO2 on solid oxide cells at high temperature (~800∘C). Electrodes were developed on commercial standard YSZ supports using Ni(M)x/YSZ mixtures for cathode and LSM/YSZ mixtures for the anode. Electron microscopy and X-ray diffraction were used to characterize the electrode architecture and material.The electrodes were tested using online mass spectroscopy and operando Raman spectroscopy. Ni/YSZ electrodes showed sustained performance only when H2 was added to the fuel mixture, and the reaction proceeded through a reverse water gas shift reaction (RWGS) (CO2 + H2 → CO + H2O) in conjunction with water electrolysis with the CO originating from non-electrochemical RWGS reaction.The reactions were also analyzed using electrochemical impedance spectroscopy. The pure Ni/YSZ cathodes showed deactivation under a pure CO2 atmosphere with the formation of NiOx species with the catastrophic breakdown at high current densities around 400 mA/cm2. The behaviour could be verified using both mass spectroscopy and operando Raman Spectroscopy. The electrochemical performance of various electrodes was compared using a 3-electrode geometry. Mixed metal oxide electrodes such as Ni(M) showed improved kinetics, with significant improvement seen in the charge transfer resistance measured. Figure 1