Exploring heterogeneous phases in highly A-site-deficient titanate with Ni exsolution

Abstract

In-situ exsolution technique, as an efficient and controllable strategy of surface modification, has been extensively applied in reversible solid oxide cells (RSOCs). Here, we demonstrate LaxSrxTi0.9Ni0.1O3-δ fiber decorated by exsolved Ni nanoparticles and highlight the impacts of A-site deficiency on Ni exsolution and electrochemical performance of RSOCs. The La0.4Sr0.4Ti0.9Ni0.1O3 (A/B = 0.8) fibrous fuel electrode decorated by Ni nanoparticles with moderate Ni exsolution displays optimum electrochemical performance at 800 °C, achieving ∼540 mW cm−2 in SOFC mode and −0.742/0.385 A cm−2 under 1.3/0.7 V in RSOC mode. In contrast, high A-site deficiency (A/B < 0.8) allows heterogeneous phases (NiTiO3) and excessive Ni exsolution along with alterations of fibrous morphology, leading to slow gas diffusion, sluggish catalysis, and Ni agglomeration. The distribution of relaxation time (DRT) results show that the rate-limiting steps in symmetrical cells are gas diffusion, hydrogen adsorption, and dissociation, accounting for over 89% of the total RP. Ni-equilibrium model based on X-ray Rietveld refinement calculates the degree of exsolution with various A-site deficiency, revealing NiTiO3 is the key factor of excessive exsolution. Our work of high A-site deficiency exemplified here may serve in the design and nanoengineering of fibrous ABO3 perovskite oxides for RSOCs.