A nanostructured ceramic fuel electrode for efficient CO2/H2O electrolysis without safe gas

Abstract

There is increasing interest in converting CO₂/H₂O to syngas via solid oxide electrolysis cells (SOECs) driven by renewable and nuclear energies. The electrolysis reaction is usually conducted through Ni–YSZ (yttria stabilized zirconia) cermets, state-of-the-art fuel electrodes for SOECs. However, one obvious problem for practical applications is the usage of CO/H₂ safe gas, which must be supplied to maintain the electrode performance. This work reports a safe gas free ceramic electrode for efficient CO₂/H₂O electrolysis. The electrode has a heterogeneously porous structure with Sr₂Fe_1.5Mo_0.5O_6−δ (SFM) electrocatalyst nanoparticles deposited onto the inner surface of the YSZ scaffold fabricated by a modified phase-inversion tape-casting method. The nanostructured SFM–YSZ electrodes have demonstrated excellent performance for CO₂–H₂O electrolysis. For example, the electrode polarization resistance is 0.25 Ω cm² under open circuit conditions while the current density is 1.1 A cm⁻² at 1.5 V for dry CO₂ electrolysis at 800 °C. The performance is comparable with those reported for the Ni–YSZ fuel electrodes, where safe gas must be supplied. In addition, the performance is up to one order of magnitude better than those reported for other ceramic electrodes such as La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ and La_0.2Sr_0.8TiO_3+δ. Furthermore, the electrode exhibits good stability in the short-term test at 1.3 V for CO₂-20 vol% H₂O co-electrolysis, which produces a syngas with a H₂/CO ratio close to 2. The reduced interfacial polarization resistance, high current density, and good stability show that the nanostructured SFM–YSZ fuel electrode is highly effective for CO₂/H₂O electrolysis without using the safe gas, which is critical for practical applications.