Highly active bifunctional LaMO 3 (M=Cr, Mn, Fe, Co, Ni) perovskites for oxygen reduction and oxygen evolution reaction in alkaline media Areeba Hameed,Khulood Logade, Naba Ali, Priya Ghosh, Sadiyah Shafath, Sumaiya Salim, Anchu Ashok, Anand Kumar * , Mohd Ali H Saleh Saad Department of Chemical Engineering, Qatar University, P O Box - 2713, Doha, Qatar * email: akumar@qu.edu.qa Abstract: Lanthanum based electrocatalytically active perovskites, LaMO 3 (M=Cr, Mn, Fe, Co, Ni), were synthesized using a single step solution combustion synthesis technique. The perovskites showed exceptional performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline medium. Based on the experimental results and literature survey, it is suggested that the exceptional 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. Introduction Mechanism of ORR /OER in Pervoskites Unit cell ABO 3 perovskite structure Possible 3d orbital electronic configuration Proposed four electron ORR and OER mechanism on perovskite surface Low e g orbital filling strong adsorption of oxygenated species on the B site (strong B-OH bond) High e g orbital filling weak adsorption of oxygenated species that limits the reaction through the slow adsorption of reactants Optimize the e g =1 Balance the adsorption and desorption of reactants and the intermediate  A fuel cell is a device that generates electricity by a chemical reaction.  Every fuel cell has two electrodes called, respectively, the anode and cathode.  Alkali fuel cells operate on compressed hydrogen and oxygen.  They generally use a solution of potassium hydroxide in water as their electrolyte.  Efficiency is about 70 percent  Alkali cells were used in Apollo spacecraft to provide both electricity and drinking water.  However, their platinum electrode catalysts are expensive.  Develop a non-precious and readily available bifunctional catalyst suitable of simultaneously activating the ORR and OER.  Combining the two functionalities in one single bifunctional oxygen redox electrode would greatly simplify the design of energy conversion devices or enhance the mobility and power-to-weight ratio  −   +    +  − →  −  − 4 − → 2 2  +  2 +4  − Catalyst Preparation HOT PLATE SOLUTION METAL NITRATE WATER FUEL Combustion front movement Key features: Molecular level homogenization ,high temperature ( ~1000 ˚C), short process time, evolution of gases, porous and high surface area Volume combustion synthesis Catalyst Characterization X-ray diffraction pattern of a) LaMO 3 (M=Cr,Fe,Mn,Co,Ni) at =1 b) LaCrO 3  LaNiO 3 particularly contain two different phases, LaNiO 3 and NiO,  All other compounds are completely in the perovskite form.  Combustion temperature obtained at φ =0.5 and φ = 2.5 does not provide enough energy for the crystallite structure formation. HRTEM image and c) SAED pattern of LaCoO3 (d-g) EDX elemental mapping of La, Co and overlapped La-Co. HRTEM image and c) SAED pattern of LaMnO3 (d-g) EDX elemental mapping of La, Mn and overlapped La-Mn.  The particle distribution over selected region on LaMnO 3 and LaCoO 3 suggests the presence of particles in the range between 8 -20 nm along with some level of agglomeration.  . EDX elemental mapping indicates the presence of La and Mn in equal ratio everywhere on the catalyst Particle size distribution histogram of a) LaMnO 3 b) LaCoO 3 Electrocatalytic ORR/OER Reaction Ag/AgCl single junction Platinum coil O 2 Reference 1. Ashok, Anchu, et al Journal of Electroanalytical Chemistry 809 (2018):22-30. 2. Kumar, A et al AIChE Journal 57.8 (2011):2207-2214. 3. Jung, Jae ‐ Il, et al. "Angewandte Chemie 126.18 (2014): 4670-4674. 4. Suntivich, Jin, et al. Nature chemistry 3.7 (2011): 546. Acknowledgement This work was made possible by UREP grant (UREP24-001-2-001) from the Qatar national research fund (a member of Qatar foundation). The statements made herein are solely the responsibility of the author(s). Conclusion  LaMnO 3 shows the maximum current density for oxygen reduction reaction, whereas LaCoO 3 shows better performance for oxygen evolution reaction.  The ORR kinetics was improved in the order of LaCrO 3 < LaFeO 3 < LaNiO 3 < LaCoO 3 < LaMnO 3 .  Chronoamperometric results show that at -0.5V LaMnO 3 holds the maximum current density with poor stability.  The LaCoO 3 catalyst showed better stability for oxygen reduction and oxygen evolution reactions with continuous cycling for 2000 cycles between -0.3V to 0.6V PINE instruments bipotentiostat (WaveDriver 20) connected with rotating disc electrode (RDE) Speed – 400 to 1600 rpm n – number of electron transfer Cyclic voltammogram for Lanthanum based perovskites in 1M KOH electrolyte in the potential window (i) -0.8V to 0.4V (ii) -0.8V to 0.8V. (a) Linear sweep voltammetry of all La-perovskites in O2 saturated 1M KOH at 50 mVs-1 at 1600 rpm in the potential range of -0.9V to 0.8V, (b) oxygen reduction reaction (ORR) current densities at 1600 rpm (c) OER current densities in the potential between 0.3V to 0.8V, d) ORR current density of LaMnO 3 at different rotation speed (400 to 1600rpm) (a) Koutecky-Levich plot at different rotation and represented the overall electron transfer in the reaction (b) kinetic current densities of La-based perovskite catalysts a) CA curve obtained at -0.5 V in O2 saturated 1M KOH solution (b) Relative current to measure the cathodic stability of LaMnO3 and LaCoO3 Electrochemical stability of LaCoO3 in (a) ORR and (b) OER curves before and after 2000 CV cycle Tafel plot comparing the activity of perovskite catalyst for (a) ORR, and (b) OER in O2 saturated 1 M KOH electrolyte at room temperature at 1600 rpm rotation speed. Undergraduate Student, Science and Engineering