Abstract
SO2-depolarized electrolysis (SDE) is the hydrogen-producing step of the hybrid sulfur (HyS) process. In this study, electrochemical impedance spectroscopy (EIS) is used to study the composition of cell voltage of SDE electrolyzers, which apply porous graphite felts as diffusing layers. By measuring the open circuit potential, the possible side reactions and the methods to avoid the side reactions are discussed from the perspectives of thermodynamics and kinetics. According to EIS results obtained at different voltages, the impedance and its components are determined by equivalent circuit fitting calculation. The obtained impedance values of different cells agree very well with their SDE performance results. The voltage loss in the SDE process is split into ohmic impedance loss, kinetics impedance loss and concentration polarization impedance loss. The influences of the graphite felt compression ratio, operating temperature and anolyte flow rate on the impedance and performance of SDE cell are investigated.
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