Influence of dynamic operation on solid carbon production by molten carbonate electrolysis

The dynamic operation of current density positively impacts metal deposition and CO₂ electrolysis for syngas production but negatively affects water electrolysis efficiency. This paper investigates the influence of applied dynamic current density with various waveforms during CO₂ electrolysis in molten Li₂CO₃, using a titanium cathode and a nickel anode. Five current waveforms are studied: triangular, square, sine, ramp-up, and ramp-down. The triangular waveform achieves the highest Faraday efficiency (FE), up to 51.5%, and the ramp-down waveform obtains the lowest specific electrical energy consumption (SEC) of 25.9 kW h kg^-1 for solid carbon production. The characteristics of solid carbon products for each waveform are investigated using x-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray fluorescence (XRF). The different current waveforms have a minimal effect on the morphology of the product, generally resulting in a spherical onion shape, with a small fraction of tubular structures. Nickel, nickel oxide, and titanium oxide are found along with carbon, indicating that metal release cannot be prevented by dynamic current density. This study provides insights into the application of different current waveforms during CO₂ electrolysis, revealing different values for FE and SEC, but limited effect on the morphology of solid carbon products.