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Abstract:
Molten carbonate electrolysis (MCE) is a promising high-temperature route to upgrade CO2-rich biogas into a higher heating value fuel while enabling CO2 separation and utilization. This paper proposes and experimentally evaluates a biogas upgrading concept based on a three-cell MCE stack operated on synthetic biogas mixtures. The stack is fed with CH4/CO2/H2O at the cathode and air at the anode and powered by external electricity, representative of surplus renewable power. Electrochemical performance is assessed through current-voltage characteristics and steady-state operation at selected current densities, while product-gas compositions are quantified by gas chromatography. The results demonstrate stable stack operation on biogas-type feeds and show that MCE can simultaneously remove CO2 and enrich the cathodic stream in H2 (and CO), thereby increasing the lower heating value compared with the raw biogas. From the measured data, key process indicators such as CO2 removal degree, gas upgrading factor, and specific electrical energy consumption are derived and discussed. The study establishes molten carbonate electrolysis as a viable and flexible option for biogas upgrading and valorization, particularly in systems coupled to intermittent renewable electricity. Unlike conventional separation-based routes (water scrubbing, PSA, membranes) that vent the captured CO2, or SOE-based power-to-methane systems that require a separate methanation reactor, MCE simultaneously removes CO2 and generates H2/CO within a single high-temperature unit. The present results provide the first experimental evidence that a multi-cell MCE stack can serve as a viable and load-flexible pathway for biogas upgrading and valorization, particularly when coupled with intermittent renewable electricity.

Keywords:
Molten carbonate electrolysis, Biogas upgrading, CO2 separation, High-temperature electrochemical conversion, Syngas and hydrogen enrichment