A-Site Modulation of Co-Ir Based Double Perovskite Oxides (A₂CoIrO₆, A = Sr, Nd, Pr, and Sm) for Maximization of Water Oxidation and Hybrid Electrolysis Derived Isopropanol Upconversion in Acid Medium

For the industrial-scale production of hydrogen via water electrolysis, water splitting in acidic conditions is in forefront compared to that in alkaline medium. However, the lack of earth-abundant, cost-effective, highly active, and durable anode electrocatalysts has impeded industrial scaling. Owing to the exceptional activity and stability in an acidic medium, Ir based multimetal perovskite oxides have evolved as prime candidates for the acidic oxygen evolution reaction (OER). Excluding very low Ir loading, Ir based double perovskite oxides also provide abundant structural and compositional flexibility, so maximization of activity and stability could be grasped by tuning the A-site and B-site ions in A₂BIrO₆. Changing the ionic radii and oxidation state of the A-site cation has a crucial impact on determining the electrocatalytic OER activity of these perovskites. Herein, we synthesized variable lanthanide based double perovskites, viz., Pr₂CoIrO₆, Nd₂CoIrO₆, Sm₂CoIrO₆, and nonlanthanide Sr₂CoIrO₆. Nd₂CoIrO₆ showed the best OER activity and needs only 234 mV overpotential (η) to acquire a current density of 10 mA cm^-2 with a mass activity of 0.69 A/mg_Ir (η = 300 mV) and excellent catalytic stability of 48 h. Density functional theory (DFT) calculations reveal that the d-band center of Nd₂CoIrO₆ perovskite is in close proximity to the Fermi level, underscoring its increased potential for the OER in agreement with experimental findings. Notably, valence and conduction band edges are primarily influenced by the O(p) and Ir(d) orbitals, with a minor contribution from the Co(d) states. The overall performance of Nd₂CoIrO₆ outperforms that of benchmark IrO₂ and most of the state-of-the-art catalysts reported so far. Nd₂CoIrO₆ was further explored for isopropyl alcohol oxidation. Excellent selectivity and faradaic yield for acetone was observed. Particularly in acidic isopropanol solution, a potential advantage of 210 mV at 10 mA cm^-2 (compared to OER) was found to oxidize isopropanol into value-added chemicals, viz., acetone, along with the generation of hydrogen.