Development of Bifunctional Oxygen Electrocatalysts Using Solution Combustion Synthesis For Fuel Cell Applications

Abstract

Advanced energy storage and conversion systems such as fuel cells and metal air batteries achieved wide attention. Oxygen reduction reaction (ORR) and Oxygen evolution reaction (OER) are the prominent reactions that govern the charging and discharging capability of batteries as well as fuel cells. The bifunctional electrocatalyst that can be used to activate both the reactions (ORR and OER) are demanding and still challenging. Platinum (Pt) group metals are found to be the most efficient electrocatalyst, but their high cost and limited availability restrains large scale commercialization. Intensive research focused on developing highly active, costeffective and earth abundant materials for bifunctional oxygen electrocatalyst for next generation energy sources. In this work, we mainly focused on the solution combustion synthesis (SCS) method for preparing nanoparticles and studying their bifunctional electrocatalytic performance in alkaline medium. The structure, physio-chemical nature and composition of the material can be tuned by the synthesis condition that enables us to correlate them with the catalytic performance for oxygen reactions. In SCS technique, the fuel to oxidizer ratio (φ) is identified as a critical parameter affecting the properties of the synthesized nanoparticles. In the first part of this study, we prepare cobalt nanoparticles with different fuel ratio (φ = 0.5, 1 and 1.5). Then we synthesized bimetallic Ag-M (Cu and Co) using three different modes of SCS. The phase distribution of the catalyst after stability shows a clear phase de-alloying and segregation of elements that reduces the performance. Thereafter, we focused on perovskite materials LaMO3 (M = Cr, Mn, Fe, Co, Ni) with stable and homogeneous perovskite phases. LaMnO3 shows the maximum current density for ORR, whereas LaCoO3 shows best performance for OER. Finally, we focused on enhancing the surface area of perovskite by incorporating a leachable salt (e.g. KCl) during combustion that breaks down the three-dimensional crystalline structure to restrict post combustion agglomeration and sintering, which in-turn translates into better electrocatalytic performance. Based on these results, we conclude that the salt assisted SCS has the potential for preparing highly efficient and durable bifunctional electrocatalyst suitable for fuel cells and metal air batteries.