Pulse regulation enables retained thickening of Mo2C films during molten-carbonate electroreduction

Retaining electrochemically generated carbide films on reactive metal substrates is limited by the coupling between carbon supply, substrate consumption, and product detachment. Here, Mo electrodes in LiCl-KCl-K 2 CO 3 melts were used to examine how pulse regulation controls retained Mo 2 C film growth during carbonate electroreduction. Although Ni and Mo showed similar cyclic voltammetric responses in the main carbonate-reduction region, phase and microstructural analyses revealed a substrate-dependent pathway on Mo. High current density produced dendritic carbonaceous deposits together with Mo 2 C, whereas low current density suppressed isolated carbon deposition and promoted interfacial Mo 2 C formation. However, prolonged galvanostatic electrolysis continuously consumed the near-surface Mo substrate, generated a porous support region, and caused Mo 2 C detachment. The collected detached products agreed with the calculated Mo2C-equivalent mass, showing that formation was not the limiting step; retention was. Pulse electrolysis resolved this formation-detachment behavior by temporally regulating carbon supply and interfacial reaction. A continuous Mo 2 C layer formed at the early stage and thickened to approximately 35 μm as a surface-retained layer. These results refine the post-carburization view of Mo 2 C growth and identify pulse regulation as a route for retained carbide-film growth during molten-carbonate electroreduction.