Integrated Co-Electrolysis and Syngas Methanation for the Direct Production of Synthetic Natural Gas from CO2 and H2 O.

The concept of an integrated power-to-gas (P2G) process was demonstrated for renewable energy storage by converting renewable electrical energy to synthetic fuels. Such a dynamically integrated process enables direct production of synthetic natural gas (SNG) from CO2 and H2 O. The produced SNG can be stored or directly injected into the existing natural gas network. To study process integration, operating parameters of the high-temperature solid oxide electrolysis cell (SOEC) producing syngas (H2 +CO) mixtures through co-electrolysis and a fixed bed reactor for syngas methanation of such gas mixtures were first optimized individually. Reactor design, operating conditions, and enhanced SNG selectivity were the main targets of the study. SOEC experiments were performed on state-of-the-art button cells. Varying operating conditions (temperature, flow rate, gas mixture and current density) emphasized the capability of the system to produce tailor-made syngas mixtures for downstream methanation. Catalytic syngas methanation was performed using hydrotalcite-derived 20 %Ni-2 %Fe/(Mg,Al)Ox catalyst and commercial methanation catalyst (Ni/Al2 O3 ) as reference. Despite water in the feed mixture, SNG with high selectivity (≥90 %) was produced at 300 °C and atmospheric pressure. An adequate rate of syngas conversion was obtained with H2 O contents up to 30 %, decreasing significantly for 50 % H2 O in the feed. Compared to the commercial catalyst, 20 %Ni-2 %Fe/(Mg,Al)Ox enabled a higher rate of COx conversion.

Power-to-Syngas: An Enabling Technology for the Transition of the Energy System?

Power-to-X concepts promise a reduction of greenhouse gas emissions simultaneously guaranteeing a safe energy supply even at high share of renewable power generation, thus becoming a cornerstone of a sustainable energy system. Power-to-syngas, that is, the electrochemical conversion of steam and carbon dioxide with the use of renewably generated electricity to syngas for the production of synfuels and high-value chemicals, offers an efficient technology to couple different energy-intense sectors, such as "traffic and transportation" and "chemical industry". Syngas produced by co-electrolysis can thus be regarded as a key-enabling step for a transition of the energy system, which offers additionally features of CO2 -valorization and closed carbon cycles. Here, we discuss advantages and current limitations of low- and high-temperature co-electrolysis. Advances in both fundamental understanding of the basic reaction schemes and stable high-performance materials are essential to further promote co-electrolysis.