The role of space charge at metal/oxide interfaces in proton ceramic electrochemical cells

Abstract

The contact potential and the resulting charge accumulation or depletion at the electrode/electrolyte interface are investigated for Ni and Cu group metals in contact with the state-of-the-art proton conductor acceptor-doped BaZrO3 by first-principles calculations and thermodynamic modeling. The contact potential depends on the metal’s work function and the defect chemical properties of the oxide, rendering it strongly temperature and atmosphere dependent. Above 900 K, most metals yield negative contact potentials and enrichment of protonic charge carriers at the electrode/electrolyte interface, facilitating charge transfer. Below 600 K, the contact potentials vary from positive to negative depending on the metal’s work function. As such, higher work function metals lead to a space-charge contribution to the electrode impedance at lower temperatures. The prospects of exploiting charge accumulation (or depletion) characteristics of such interfaces are furthermore discussed with a focus on nanocomposite electrodes and solid-state electrochemical capacitors.