Deconvoluting Sources of Overpotential of Oxide Ion Conducting Membrane Assisted Inert Anode

Inert anode assisted by using oxide ion conducting membranes, such as yttria-stabilized zirconia (YSZ), offers a sustainable alternative to traditional graphite anodes for molten salt electrolysis by enabling oxygen evolution instead of CO2 emission. However, the polarization behavior as well as the different sources of overpotential of such anode has not been thoroughly investigated. This work systematically deconvolutes the overpotential of an oxide ion conducting membrane assisted inert anode into three components, i.e., ohmic overpotential (η ohmic), anodic catalytic overpotential (η catalyst), and mass transport overpotential (η mt), by combining insights from multiple electrochemical techniques. Quantitative analysis provides strong evidence for the existence of the diffusion boundary layer near the molten salt/YSZ interface. We demonstrate that forced convection can significantly reduce η mt by thinning the diffusion boundary layer near the molten salt/YSZ interface. Conversely, η catalyst remains independent of the concentration of oxide ions, governed instead by oxygen exchange kinetics at the catalyst. These findings highlight strategies to optimize electrolysis efficiency, including enhancing oxide ion supply by forced convection, employing optimized catalysts and reducing ohmic losses from the oxide ion conducting membrane.