Combustion synthesis of bifunctional LaMO3 (M = Cr, Mn, Fe, Co, Ni) perovskites for oxygen reduction and oxygen evolution reaction in alkaline media

Lanthanum based electrocatalytically active LaMO3 (M = Cr, Mn, Fe, Co, Ni) perovskites were synthesized using a single step solution combustion technique. The structural and morphological properties of the catalysts were studied using XRD, SEM, and TEM. The synthesis conditions are found to have a siginificant effect on the nature of the nanoparticles and it can be tuned to synthesize amorphous or crystalline materials. The perovskites showed exceptional performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline medium. LaMnO3 is found to be most active for ORR, whereas LaCoO3 for OER. The onset potential of LaMnO3 is - 0.12 V, and for other La-transition metals is nearly - 0.2 V. The Koutechy-Levich plot obtained from rotating disk electrode shows a higher number of electron transfer for LaMnO3 catalyst and the least for LaCrO3, whereas the stability results indicate the LaCoO3 to be more stable as compared to LaMnO3. Based on the experimental results and literature survey, it is suggested that the improved activity of Mn and Co based lanthanum perovskite catalyst could be due to the optimum stabilization of reaction intermediates involved in the rate-determining step (RDS) of ORR/OER.