Rational Identification of Doping Strategy to Achieve a Highly Conductive and Reliable Protonic Electrolyte for Electrochemical Cells

Abstract

While protonic ceramics are being utilized as electrolyte materials in electrochemical cells for hydrogen or electricity production, the higher proton conductivity and chemical stability under realistic operating conditions are required to deliver fast proton flux. For widely used Y or/and Yb doped Ba(Ce,Zr)O 3 electrolytes, there are still some concerns with indistinct doping mechanism and uncertain element precipitation problem during sintering, which raise practical problem on electrolyte selection. In this work, the strategy of single element doping and co-element doping has been investigated to understand how they behave differently in proton conductivity and chemical instability. Three compositions, BaCe 0.4 Zr 0.4 Y 0.2 O 3-δ , BaCe 0.4 Zr 0.4 Yb 0.2 O 3-δ and BaCe 0.4 Zr 0.4 Y 0.1 Yb 0.1 O 3-δ , are chosen to study the overall conductivity as function of B-site environment and gas conditions to provide experimental evidences for composition optimization. More importantly, the Y or/and Yb precipitation in each composition under various sintering conditions is extensively studied to explore the safe window for sintering the electrolyte with minimal element diffusion. In addition, the diffusion of nickel element into the electrolyte grain is also studied to understand the detrimental effects on grain boundary conductivity and consequently the electrochemical performance in the cells. This study will provide some insights into protonic electrolyte selection based on technical considerations on both excellence and stability.