Synthesis of La<sub>2</sub>NiMnO<sub>6</sub> Double Perovskite as a Highly Selective Electrocatalyst for Oxygen Reduction to Hydrogen Peroxide in Electrochemical Energy Conversion
Mohammad Imran Hossain, Syed Abdul Monim, Zannatul Mumtarin Moushumy, Neamul H. Khansur, Iqbal Mahmud, Mostafizur Rahaman, Ali Aldalbahi, Shakhawat H. Firoz, Mohammad A. Hasnat
Abstract
Oxygen reduction reaction (ORR), a key process in sustainable energy conversion, utilizing a perovskite catalyst to achieve higher currents at lower overpotentials along with the production of value-added product hydrogen peroxide (H 2 O 2 ), serves the dual functionality of both energy production and a green route for H 2 O 2 generation. Here, we report the synthesis of a highly efficient double perovskite La 2 NiMnO 6 (LNMO), achieved through the incorporation of two transition metals, Ni and Mn, in the perovskite structure, and explore its activity for ORR. During ORR at a rotation rate of 1600 rpm in 1.0 M NaOH, LNMO exhibits an onset potential of 0.75 V (corresponding to a current density of 0.1 mA cm –2 ) and a Tafel slope of 95 mV dec –1, achieving over 88% H 2 O 2 selectivity and 73% faradaic efficiency across a wide potential range of 0.2–0.6 V vs RHE. Characterization techniques including OCP, EIS, ICP-OES, XRD, XPS, FE-SEM, and FTIR confirmed the successful preparation of LNMO and its catalytic activity. The kinetic investigation unveiled by the transfer coefficient (α) demonstrated that ORR on the LNMO surface followed a stepwise mechanism, involving an overall two irreversible electron transfer steps, where the first electron transfer was the rate-determining step. The analyses further revealed a diffusion-limited process for ORR accompanied by first-order kinetics with a standard rate constant ( k 0 ) of 3.97 × 10 –3 cm s –1 and a formal potential ( E 0 ) value of 0.96 V vs RHE. Finally, a stability test via chronoamperometry showed that LNMO outperformed the Pt/C catalyst.