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High-temperature solid-oxide CO2 electrolysers enable high-efficiency conversion of electrical energy to valuable fuels and chemicals and as such facilitate a sustainable-energy technology. Conventional cermet-based fuel electrodes used in such solid-oxide cells (SOCs) like nickel–yttria-stabilized zirconia (Ni–YSZ) suffer from morphological degradation and destructive carbon deposition. In recent years, there has been an increasing interest in employing single-phase ceria-based fuel electrodes, which are known to exhibit excellent carbon deposition resistance. Under sufficiently reducing conditions, doped ceria (substituted with trivalent cations such as samarium or gadolinium to generate mobile oxygen vacancies) becomes a mixed ionic–electronic conductor, showing appreciable electronic conductivity. Here, we show for the first time stable high performance in CO2 electrolysis using a ceria-based SOC. The single full cell incorporating a 10 mol% gadolinium-doped ceria (GCO) fuel electrode delivers a current density as high as 1.51 A cm−2 at 800 °C during pure CO2 electrolysis, which is the best electrode performance reported to date among all-ceramic cathode materials. We demonstrate that the electrode performance in CO2 electrolysis is linked with the electronic conductivity, and hence, with the electronic charge carrier concentration in GCO. The results of the present work pave the way for development of robust, nickel-free SOCs for direct CO2 electrolysis. [ABSTRACT FROM AUTHOR]

A dense Ce0.9Gd0.1O2−d (GDC) interlayer is an essential component of the SOFCs to inhibit interfacial elemental diffusion between zirconia‐based electrolytes (eg YSZ) and cathodes. However, the characteristic high sintering temperature of GDC (>1400°C) makes it challenging to fabricate an effective highly dense interlayer owing to the formation of more resistive (Zr,Ce)O2 interfacial solid solutions with YSZ at those temperatures. To fabricate a useful GDC interlayer, we studied the influence of transition metal (TM) (Co, Cu, Fe, Mn, & Zn) doping on the sintering and electrochemical properties of GDC. Dilatometry data showed dramatic drops in the necking and final sintering temperatures for the TM‐doped GDCs, improving the densification of the GDC in the order of Fe > Co > Mn > Cu > Zn. However, the electrochemical impedance data showed that among various transition metal dopants, Mn doping resulted in the best electrochemical properties. Anode supported SOFCs with Mn‐doped, nano, and commercial‐micron GDC interlayers were compared with regard to their performance and stability levels. Although all of the SOFCs showed stable performance, the SOFC with the Mn‐doped GDC interlayer showed the highest power density of 1.14 W cm−2 at 750°C. Hence, Mn‐doped GDC is suggested for application as an effective diffusion barrier layer in SOFCs. [ABSTRACT FROM AUTHOR]