Methane Production via Al₄C₃ Electrodeposition from CO₂ at an Al Electrode/NaCl-CaCl₂ Melt Interface

This study proposes a new process for methane production from CO 2 and H 2 O via Al 4 C 3 formation by electrochemical reduction of CO 2 -derived CO 3 2− ions on an Al electrode in NaCl-CaCl 2 -CaO melt at 873 K. The electrodeposited Al 4 C 3 can generate methane through a spontaneous chemical reaction with water. The proposed process was demonstrated by electrochemical measurements, X-ray diffraction, thermodynamic evaluation, and quantitative analysis of the gas generated by the reaction between the Al 4 C 3 and water. The effects of applied potential, electrolytic time, and additives into the melt on the current efficiency of methane were investigated. It was found that methane was obtained with a maximum current efficiency of 63 ± 2.5% when potentiostatic electrolysis was performed at 0.45 V for 5 min in the melt containing 6.0 mol% Al 4 C 3 under CO 2 atmosphere, although that was less than 10% in the system without Al 4 C 3 . The addition of Al 4 C 3 before electrolysis prevented the dissolution of the electrodeposited Al 4 C 3 into the melt. Based on the results, the formation mechanism of Al 4 C 3 on the Al electrode is discussed. The novel process of methane synthesis doesn’t need reducing agents, such as hydrogen. It is also possible to obtain CO 2 -derived methane when needed by storing methane sources as solid Al 4 C 3 .