Boosting alkaline water electrolysis by asymmetric temperature modulation

Abstract

Hydrogen production by water electrolysis is a sustainable and promising pathway to store surplus electricity from intermittent renewable energy. In conventional electrolyzers, hydrogen evolution and oxygen evolution reactions at the two electrodes run at the same temperature. In this work, we implement an asymmetric temperature modulation to enhance the water electrolysis rate in an alkaline solution. We revisit the thermodynamics of water electrolysis and determine by both simulations and experiments that the Gibbs free energy change required for alkaline water electrolysis under asymmetric temperature is lower than that under uniform average temperature. With the temperature difference of 40 K (possible for low-grade waste heat), the required voltage of asymmetric configuration decreases by 100 mV at the current density of 10 mA cm−2 compared to the system operated at the same average temperature. Moreover, the thermal efficiency reaches a maximum value of 7% under optimized operating current density. The asymmetric-temperature water electrolysis opens a promising way for utilization of low-grade heat.