Mixed Metal Cathodes for CO2 Electroreduction Using Solid Oxide Electrodes

Abstract

Electroreduction of CO2 to fuels through the use of renewable energy provides a beneficial route and it decreases the reliance on fossil fuels. The electrochemical reduction of CO2 to hydrocarbon fuels (CHx) is highly energy inefficient owing to kinetic limitations which are a direct consequence of multistep-multielectron transfer process. The selective formation of CO from CO2 is energy efficient. CO thus formed, serves as a valuable source of energy as it can be directly used as a fuel. Moreover, it can be further converted into hydrocarbon fuels via Fischer-Tropsch reactions using green hydrogen. We hereby propose Ni(M)x/YSZ based electrodes for electroreduction of CO2 on solid oxide cells at high temperature (~800∘C). Electrodes were fabricated on commercial standard YSZ supports using Ni(M)x/YSZ and LSM/YSZ mixtures which were respectively employed as materials for that cathode and anode. Characterisation of the developed electrode architecture was carried out via electron microscopy and X ray diffraction.The behaviour of electrodes during CO2 electrolysis was analysed through online mass spectrometry and operando Raman spectroscopy. Ni/YSZ electrodes displayed sustained performance only upon the addition of H2 to the fuel mixture. The reaction progressed through a reverse water gas shift reaction (RWGS) (CO2 + H2 à CO + H2O) along with water electrolysis where CO originates from non-electrochemical RWGS reaction.Electrochemical impedance spectroscopy was employed to analyse the reactions. Three electrode assembly was used to compare the electrochemical performance of the various electrodes. The pure Ni/YSZ cathodes showed deactivation under pure CO2 atmosphere. Mixed metal oxide electrodes such as Ni(M)x exhibit enhanced performance for CO2 electrolysis in both pure CO2 as well as in the presence of 5% H2. Catalytic performance of the electrodes was evaluated by varying fuel mixtures composition and temperature. Kinetics of electrode performance were evaluated using distribution of relaxation time formalism. Mixed metal oxide such as Ni(M)x showed improved kinetic with significant improvement in charge transfer resistance. Figure 1