Ameliorating La0.5Sr1.5MnO4 with Ni-doping to enhance cathode electrocatalysis for proton-conducting solid oxide fuel cells

Abstract

Cathodes with high electrocatalytic activity are critical for commercializing proton-conducting solid oxide fuel cells (H-SOFCs). Herein, B site acceptor Ni-doping is first attempted to ameliorate manganite-based Ruddlesden–Popper phase oxide La_0.5Sr_1.5MnO_4+δ (LSMO), introducing more oxygen vacancies and new effective Ni²⁺–O–Ni³⁺ electron-hopping transition paths with an irregular structural deformation, ultimately enhancing the electrocatalysis with a 2.23 to 2.60 times improvement of electrical conductivity at 500–700 °C. The significantly enhanced oxygen/proton diffusion in the La_0.5Sr_1.5Mn_0.7Ni_0.3O_4+δ (LSMN) sample, verified via electrical conductivity relaxation results, can enhance electrocatalytic activity, enabling more efficient oxygen reduction reaction kinetics. Hence, the Ni-ameliorated LSMN cathode exhibits a prominent power output of 1342 and 668 mW cm⁻² at 700 and 600 °C on a H-SOFC, surpassing the cells with the Ni-free LSMO cathode and other LSMO-based and Ln₂NiO₄-based cathodes in the literature. On balance, the excellent power density and polarization performance, together with the superior operation stability demonstrates that the LSMN candidate is a preferable alternative to H-SOFC cathodes. This work is an attempt to design highly active electrodes by regulating the crystal structure derived from B-site acceptor-doping, which is also beneficial for new material designs in H-SOFC and related electrocatalytic fields.