Synthesis and characterization of bifunctional Ru doped La-based perovskites for magnetic refrigeration and energy storage systems

Abstract

In this study, the effect of Ru additive on the crystallographic, magnetic, and electrocatalytic properties of LaBiBaMnO3 manganite was investigated for magnetic refrigeration and energy storage systems. XRD analysis of La0·62Bi0·05Ba0·33MnO3 (LBBM) and La0·62Bi0·05Ba0·33Mn0·90Ru0·10O3 (LBBMR) manganites prepared by solid state method reveals that the samples have a rhombohedral structure and the average grain size of perovskites are found to be below 3 μm. From the temperature-dependent magnetization measurements, it was observed that the value of Curie temperature (TC) decreased from 334 K for LBBM to 327 K for LBBMR with the substitution of Mn with 10% Ru. In parallel with the decrease observed in TC with Ru contribution, a decrease in magnetic entropy value was also observed. The substitution of 10% Ru reduced the onset potential 51 mV for oxygen evolution reaction (OER) and 74 mV for oxygen reduction reaction (ORR). The electrode activity of OER at 10 mA cm−2 was obtained at around 0.976 V. Ru substitution and increasing scan rate to 100 mV s−1 increased the current density and lowered onset potential for OER. The ORR efficiency of LBBM catalysts boosted up to 60% with the durability test for 6 h. The increased cathodic Tafel slope from −255.1 mV dec−1 to −120.4 mV dec−1 with 10% Ru substitution suggests that a fast charge transfer for ORR activity due to Ru-occupied Mn-sites in the structure. LBBMR sample achieved bifunctional properties as ORR/OER performance and magnetic cooling applications by substituting Mn with 10% Ru.