High-Temperature Co-Electrolysis: A Versatile Method to Sustainably Produce Tailored Syngas Compositions

Abstract

High-temperature co-electrolysis of carbon dioxide and steam is a promising method to produce 'white' syngas by making use of renewable energy and carbon dioxide as sustainable feedstock. The technological key advantage is the possibility to tailor syngas compositions over a broad range. This paper presents a systematic investigation of the syngas tailoring process by establishing relationships between feed gas compositions and flow rates to the syngas ratio. A linear dependence between the H 2 O:CO 2 ratio in the feed gas and the H 2 :CO ratio in the output gas was observed. Furthermore, the syngas ratio remains mostly invariant upon variations in electrochemical potential and fluctuating gas utilizations/flow rates during operation of a co-electrolysis cell. Most importantly, the co-electrolysis performance was demonstrated to operate at high current densities of up to 3.2 A•cm −2 over a broad range of feed gas compositions with faradaic efficiencies of nearly 100%. The possibility to operate co-electrolysis under transient load conditions renders this method particularly suitable in future scenarios of intermittent availability of renewables. The results described here illustrate the versatility of co-electrolysis, which can produce all relevant syngas compositions in a single-step process at constantly high performance.

Sustainable Syngas Production by High‐Temperature Co‐electrolysis

“…Their conclusion was that steam is converted electrochemically while CO 2 is converted by the RWGS reaction. Our observations confirm the results for H 2 O contents in the fuel feed down to 20 % . For lower steam contents, however, the performance decreases and converges to that of pure CO 2 electrolysis.…”

“…One unique advantage of co‐electrolysis is the possibility to tailor the syngas ratio of H 2 :CO in one process step by varying the process parameters such as inlet gas composition or flow rate. The gas composition was monitored by mass spectrometry and described in detail in previous work , . The findings were that the ratio is mainly influenced by the inlet gas composition and determined by the fuel (H 2 O + CO 2 ) utilization and the RWGS reaction.…”

“…The comparison of the performance of CSCs on single cells during co‐ and steam electrolysis for gas mixtures of 50 % H 2 O + 50 % H 2 and 25 % H 2 O + 25 % CO 2 + 50 % H 2 has been reported earlier . The gas feed used during co‐electrolysis equilibrates due to the reverse water‐gas shift reaction (RWGS) occurring at the nickel in the substrate and cathode layer to the thermodynamic equilibrium composition of 38.6 % H 2 O + 11.4 % CO 2 + 36.4 % H 2 + 13.6 % CO at the operating temperature of 900 °C.…”

“…The gas feed used during co‐electrolysis equilibrates due to the reverse water‐gas shift reaction (RWGS) occurring at the nickel in the substrate and cathode layer to the thermodynamic equilibrium composition of 38.6 % H 2 O + 11.4 % CO 2 + 36.4 % H 2 + 13.6 % CO at the operating temperature of 900 °C. In the i‐V curves both mixtures show the same performance with respect to the area specific resistance (ASR) determined from the slope of the i/V curves and the current densities at the chosen maximum voltage of 1.4 V .…”

Trendbericht Technische Chemie 2021

“…Experimente und Simulationen des Ko-Elektrolyseprozesses bestätigen dies. 19) Somit bietet der Ko-Elektrolyseprozess eine ressourcenschonende und regenerative Alternative zur herkömmlichen, rein thermokatalytischen Synthesegasherstellung. Dazu dienen heutzutage noch immer die fossilen Rohstoffe Erdgas, Erdöl und Kohle.…”