Studies on Protonic Solid Oxide Cells

Abstract

In this paper, we describe new strategies to reduce the resistances related to cathode reactions and interfacial proton transfer in protonic solid oxide fuel cells (H⁺-SOFCs) based on proton-conducting BaZr_xCe_0.8−xM_0.2O_3−δ (M = Y, Yb, Sc etc.) by means of material and cell-structure design changes. First, an extension of the effective cathode reaction areas by employing the H⁺/O²⁻/e⁻ triple-conducting cathode is described. Cubic La_0.7Sr_0.3Mn_1−xNi_xO_3−δ (x = 0–0.3) can be hydrated under fuel cell conditions due to its large hydration enthalpy (∼100 kJ mol⁻¹), whereas rhombohedral La_0.7Sr_0.3Mn_1−xNi_xO_3−δ does not exhibit hydration capabilities; hence, the porous anode cermet support fuel cells (PAFCs), which use the former as a cathode, possess significantly smaller cathode polarization resistances than the PAFCs that use the latter. Second, we describe a new thermodynamic mechanism for reducing the electrolyte and cathode reaction resistances in a hydrogen-permeable metal-support fuel cell (HMFC), which involves the blocking of the oxide ion minor conduction in the BaZr_xCe_0.8−xM_0.2O_3−δ electrolyte at metal/oxide heterointerfaces. The BaZr_xCe_0.8−xM_0.2O_3−δ membrane of HMFCs is forced to gain extra protons to compensate for the charge from the oxide ions accumulating near the heterointerfaces via blocking, resulting in extremely high proton conductivity. This promotes significant interfacial proton diffusion for cathode reactions.