A cascaded gas-liquid separator for multi-stack series configuration to improve the current efficiency of an alkaline water electrolysis system

The high conductivity of the alkaline electrolyte leads to shunt current paths in alkaline water electrolysis (AWE) stacks. Shunt currents do not generate hydrogen, thus decreasing the current efficiency. This impact on efficiency becomes more significant as the rated voltage of the stack increases. To mitigate this while maintaining the rated voltage, a practical approach is to divide a large stack into multiple smaller stacks and connect them in a multi-stack series configuration. This configuration effectively increases the shunt resistance, thereby reducing the shunt currents in the stacks. However, existing literature lacks a detailed discussion of this configuration that considers the impact of process equipment on current efficiency, especially with more than three stacks in series. This leads to the absence of a method that can fulfill the industrial need for an AWE system with high efficiency, large capacity, and high voltage. To fill this gap, this paper proposes a novel Cascaded Gas-Liquid Separators (CGLS) architecture based on a detailed circuit analysis of the multi-stack series configuration. This architecture employs a cascaded arrangement by routing the electrolyte through alternating stacks and separators, thus allowing more stacks to be connected in series. To demonstrate this, a proof-of-concept on a 10 kW AWE prototype with a multi-stack series configuration and CGLS architecture was provided. A practical control strategy was proposed to ensure the stability of liquid levels and pressure in the separators. A comprehensive model of the AWE-CGLS architecture was built, and its scalability for the multi-stack series configuration was demonstrated. The results showed that the CGLS architecture maintained the same current efficiency as each single stack, demonstrating its potential for improving current efficiency during AWE scale-up. A case study indicates that when an 8-stack series configuration with AWE-CGLS architecture is employed, the current efficiency of a 10 MW AWE system can be increased to 96.79 %.