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SO 2 -depolarized electrolysis (SDE) is the key process in the hybrid sulfur cycle for green hydrogen production, but the detailed SDE characteristics including products generation, current efficiency variation, and side reactions are unclear. Herein, a continuous SDE process was experimentally conducted and theoretically modelled. The H 2 and H 2 SO 4 production was accelerated and the current efficiency for both electrodes was improved with a proper increase in current density (50−100 mA/cm2) or temperature (293−318 K), but further increasing current density to 150 mA/cm2 or temperature to 333 K led to a negative trend because of the anode corrosion or declined SO 2 solubility. The increasing initial H 2 SO 4 concentration (10−40 wt%) facilitated the cathodic H 2 production and current efficiency, while negatively influenced the anodic SO 2 conversion. The parasitic reactions occurred at cathode consumed H 2 and resulted to the cathodic current efficiency well below 100%. A rigorous mathematical regression model correlating the production rates of H 2 and H 2 SO 4 with current density, temperature, and initial H 2 SO 4 concentration was developed, and combined with the analysis of variance, current density was suggested the biggest factor affecting products generation in SDE process. These findings demonstrate a practical avenue for efficient SO 2 conversion and H 2 production in SDE process of hybrid sulfur cycle. [Display omitted] • H 2 and H 2 SO 4 production, current efficiency, and side reactions during SDE process were characterized. • Influence of current density, temperature, and initial H 2 SO 4 concentration on SDE process were emphasized. • Rigorous mathematical regression models concerning H 2 and H 2 SO 4 production rates were developed. • Current density was the biggest influencing factor toward products generation during SDE process. [ABSTRACT FROM AUTHOR]

The SO 2 -depolarized electrolysis (SDE) is one of the main processes in the hybrid sulfur cycle for hydrogen production, the microscopic characteristics of which are still not clear. In this work, a numerical analysis of SDE was conducted. The steady-state, laminar and incompressible 2D model of the electrolytic cell (EC) for carrying out SDE was first developed and verified. Physical field characterization indicated that the velocity was almost uniformly distributed in the flow channel, but higher pressure drops and pumping power consumption existed in the anode channel than in the cathode channel. Meanwhile, the continuous conversion of SO 2 to H 2 SO 4 at anode and generation of H 2 at cathode along the channel length were determined. Further exploring the impacts of three main operating parameters implied that an appropriate higher electrolytic potential, lower inlet flow rate (not less than 0.005 m/s) and operating temperature were favorable for improving the SDE. After comprehensive consideration of SDE performance and energy consumption, a feasible operating condition of 0.8 V, 303 K, and 0.005 m/s was proposed for SDE process. The developed model and microscopic characterization of SDE will favor the design and optimization of EC for SDE process. [Display omitted] [ABSTRACT FROM AUTHOR]