Selective high-temperature CO2 electrolysis enabled by oxidized carbon intermediates

Abstract

High-temperature CO2 electrolyzers offer exceptionally efficient storage of renewable electricity in the form of CO and other chemical fuels, but conventional electrodes catalyze destructive carbon deposition. Ceria catalysts are known carbon inhibitors for fuel cell (oxidation) reactions, however for the more severe electrolysis (reduction) conditions, catalyst design strategies remain unclear. Here we establish the inhibition mechanism on ceria and show selective CO2 to CO conversion well beyond the thermodynamic carbon deposition threshold. Operando X-ray photoelectron spectroscopy during CO2 electrolysis -using thin-film model electrodes consisting of samarium-doped ceria, nickel, and/or yttria-stabilized zirconia -together with density functional theory modeling reveal the crucial role of oxidized carbon intermediates in preventing carbon buildup. Using these insights, we demonstrate stable electrochemical CO2 reduction with a scaledup 16 cm 2 ceria-based solid oxide cell under conditions that rapidly destroy a nickel-based cell, leading to substantially improved device lifetime.Main Text: CO2 utilization is expected to play a key role in achieving a carbon-neutral sustainable energy economy. Electrochemical CO2 reduction, in particular, is a promising way to store intermittent electricity derived from solar and wind in the form of chemicals, such as synthetic hydrocarbons compatible with the existing energy infrastructure, and is therefore an essential technology in decarbonization strategies [1][2][3][4] . Currently, the most efficient CO2 electrolysis technology is the elevated-temperature solid oxide electrochemical cell (SOC), which utilizes O 2as the mobile ion. SOCs produce CO and O2 at the thermoneutral voltage of ~1.46 V with current densities exceeding 1 A/cm 2 -similar to steam electrolysis, which can be carried out simultaneously in the same cell to produce syngas or methane 1,2,5,6 . The same SOC can be operated in reverse as a fuel cell to re-oxidize the fuel products, thereby enabling operation as a flow battery 6,7 . Another important application is O2 (and CO) production from the CO2-rich atmosphere of Mars for rocket propulsion and life support, which will be demonstrated on the NASA Mars 2020 rover 8 .

How Rh surface breaks CO2 molecules under ambient pressure

“…However, their specific characterizations have been comparatively limited because of technical difficulties related to the decrease of the electron mean-free path at elevated pressures 19 . Eventually, the progressive tools operable in realistic conditions 20,21 are necessarily required to unravel the early steps of CO 2 RR at the molecular level. Recently published literature supports the strong evidence of CO 2 activation beyond the pressure gap, for instance, the intramolecular bond-breakage phenomenon of CO 2 molecules was reported on the Cu 22,23 and Ni 24,25 catalysts at the elevated pressures.…”

A Review of The Methanol Economy: The Fuel Cell Route

“…Graves et al recently demonstrated an interesting electrode where the current collector is substituted with Sr 0.99 Fe 0.75 Mo 0.25 O 3δ (SFM), and the catalytic activity is obtained with Pr-doped CeO 2 (CPO) nano particles [77]. Such an electrode could enable pressurized co-electrolysis of CO 2 and H 2 O, without Ni or Cu sintering, and without CH 4 formation.…”

Developments in CO2 Electrolysis of Solid Oxide Electrolysis Cell with Different Cathodes▴

“…Ceria has remarkable carbon‐suppression capability, Skafte et al. 27 studied on the surface properties of ceria and other vacancy rich oxides to further improve carbon tolerance and achieve stable and selective catalytic reactions of CO 2 .…”

“…Solutions include increasing the fuel electrode porosity and adjusting the operational conditions, while neither of them has been considered as better as replacing Ni-based material with some kinds of alternative cathode material. Ceria has remarkable carbon-suppression capability, Skafte et al [27] studied on the surface properties of ceria and other vacancy rich oxides to further improve carbon tolerance and achieve stable and selective catalytic reactions of CO 2 .…”