Synergistic Bifunctional Catalyst Design based on Perovskite Oxide Nanoparticles and Intertwined Carbon Nanotubes for Rechargeable Zinc–Air Battery Applications

Advanced morphology of intertwined core–corona structured bifunctional catalyst (IT-CCBC) is introduced where perovskite lanthanum nickel oxide nanoparticles (LaNiO₃ NP) are encapsulated by high surface area network of nitrogen-doped carbon nanotubes (NCNT) to produce highly active and durable bifunctional catalyst for rechargeable metal–air battery applications. The unique composite morphology of IT-CCBC not only enhances the charge transport property by providing rapid electron-conduction pathway but also facilitates in diffusion of hydroxyl and oxygen reactants through the highly porous framework. Confirmed by electrochemical half-cell testing, IT-CCBC in fact exhibits very strong synergy between LaNiO₃ NP and NCNT demonstrating bifunctionality with significantly improved catalytic activities of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Furthermore, when compared to the state-of-art catalysts, IT-CCBC outperforms Pt/C and Ir/C in terms of ORR and OER, respectively, and shows improved electrochemical stability compared to them after cycle degradation testing. The practicality of the catalyst is corroborated by testing in a realistic rechargeable zinc–air battery utilizing atmospheric air in ambient conditions, where IT-CCBC demonstrates superior charge and discharge voltages and long-term cycle stability with virtually no battery voltage fading. These improved electrochemical properties of the catalyst are attributed to the nanosized dimensions of LaNiO₃ NP controlled by simple hydrothermal technique, which enables prolific growth of and encapsulation by highly porous NCNT network. The excellent electrochemical results presented in this study highlight IT-CCBC as highly efficient and commercially viable bifunctional catalyst for rechargeable metal–air battery applications

Facile Synthesis and Evaluation of Nanofibrous Iron–Carbon Based Non-Precious Oxygen Reduction Reaction Catalysts for Li–O₂ Battery Applications

Development of low cost active catalysts toward oxygen reduction reaction (ORR) is critical for the effective operation of Li–O₂ battery. Porous nonprecious iron–carbon based nanofiber catalysts have been developed by electrospinning method. The catalysts demonstrated similar ORR catalytic activity for ORR as the commercial Pt-based catalysts in the aqueous half-cell voltammetry sweeps. In the Li–O₂ aprotic environment, the catalyst exhibited higher on-set potentials when compared to glassy carbon and Pt disk electrodes. The results show that the nonprecious electrospun nanofiber could be an effective low cost ORR catalyst at the cathode for Li–O₂ battery

Design of Highly Active Perovskite Oxides for Oxygen Evolution Reaction by Combining Experimental and ab Initio Studies

Perovskite oxides (ABO₃) have recently attracted attention since tailoring their chemical compositions has resulted in remarkable activity toward oxygen evolution reaction (OER) which governs rechargeability of recently spotlighted metal–air batteries and regenerative fuel cells. For further development of highly OER active perovskite oxides, however, the exact mechanism the OER must be well understood. Herein, we introduce investigation of the OER mechanism of perovskite oxides by ab initio analysis based on well-defined model systems of LaMnO₃ (LMO), LaCoO₃ (LCO), and La_0.5Sr_0.5CoO₃ (LSCO). In addition, we have systematically conducted electrochemical experiments from which we have observed an increasing trend in the OER activity in the order of LSCO > LCO > LMO based on the cyclic voltammetry (CV) results obtained in the alkaline medium. To validate the experimental results, free-energy diagrams have been constructed for oxygen intermediates on the surface of the defined models to find the limiting step by changing the B site atom (e.g., Mn and Co) and the partial displacement of Sr atoms in La site. The oxygen adsorption energy of perovskite oxides is found to increase with decreasing number of outer electrons as well as upshifting of the position of the d_<i>z</i>² orbital toward the Fermi level of B site element. This work demonstrates that highly active OER perovskite oxides can be obtained by modifying the chemical composition to finely tune the oxygen adsorption energy on the catalyst’s surface, confirmed by synergetic approaches of using both experimental and ab initio computational studies