Electrochemical Promotion of Catalysis for CO 2 Hydrogenation on Ru-Based Catalyst Using Ionically Conducting Ceramics

The release of carbon dioxide (CO 2 ) into the atmosphere has led to effects of climate change resulting in an increase in global temperature, ocean acidification and many other environmental issues. Hydrogenation of CO 2 into synthetic hydrocarbons is a promising solution in decreasing anthropogenic dependence on fossil fuels and providing an energy source that is carbon-neutral. The reverse water gas shift (RWGS) reaction is a feasible hydrogenation reaction that requires a 2-electron transfer to yield syngas (CO + H 2 ) to be used in the Fischer-Tropsch reaction to synthesize synthetic hydrocarbons. In previous work (submitted to the Journal of CO 2 Utilization), the conversion of CO 2 into CO using Ru-nanostructured metal nanoparticles dispersed on ionically conducting ceramic supports like ceria (CeO 2 ), doped-ceria (x-CeO 2 ) and yttria-stabilized zirconia (YSZ) was studied with promising results. The activity of the Ru-based nanoparticles was improved due to the ionically conductive properties of the support, which contain oxygen (O δ- ) ionic species that promote the reaction. This promotional effect is known as the metal-support interaction (MSI) where nanoparticles are dispersed on a powder support, allowing O δ- species to migrate from support to nanoparticle by an increase in temperature [1,2]. The MSI effect has been observed using the best Ru-based powder catalyst supported on samarium-doped ceria (SDC) - Ru 45 Fe 55 /SDC (2 wt.%), which yielded high CO amounts between 300-750°C. Current research aims at improving the overall RWGS reaction at lower temperatures through the utilization of the electrochemical promotion of catalysis (EPOC) or non-faradaic electrochemical modification of catalytic activity (NEMCA) effect [3,4]. EPOC allows to control in-situ the migration of ionic species to and from the metal surface through the application of a potential difference or current between the catalyst-working electrode and an inert counter electrode. This migration of species leads to the formation of a neutral double layer encapsulating Ru nanoparticles, promoting the reaction. The catalyst setup resembles an electrocatalytic cell where metal nanoparticles act as the working electrode deposited on a solid support in the form of a disc. The support (YSZ in this case) represents a fixed layer of electrolytes that conducts O δ- ions to migrate to and from the active catalyst. As shown in Fig. 1, a promotional effect is observed for Ru on YSZ at 350°C