Nickel-cobalt oxalate as an efficient non-precious electrocatalyst for an improved alkaline oxygen evolution reaction.

The quest for developing next-generation non-precious electrocatalysts has risen in recent times. Herein, we have designed and developed a low cost electrocatalyst by a ligand-assisted synthetic strategy in an aqueous medium. An oxalate ligand-assisted non-oxide electrocatalyst was developed by a simple wet-chemical technique for alkaline water oxidation application. The synthetic parameters for the preparation of nickel-cobalt oxalate (Ni 2.5 Co 5 C 2 O 4 ) were optimized, such as the metal precursor (Ni/Co) ratio, oxalic acid amount, reaction temperature, and time. Microstructural analysis revealed a mesoporous block-like architecture for nickel-cobalt oxalate (Ni 2.5 Co 5 C 2 O 4 ). The required overpotential of Ni 2.5 Co 5 C 2 O 4 for the alkaline oxygen evolution reaction (OER) was found to be 330 mV for achieving 10 mA cm geo -2 , which is superior to that of NiC 2 O 4 , CoC 2 O 4 , NiCo 2 O 4 and the state-of-the-art RuO 2 . The splendid performance of Ni 2.5 Co 5 C 2 O 4 was further verified by its low charge transfer resistance, impressive stability performance, and 87% faradaic efficiency in alkaline medium (pH = 14). The improved electrochemical activity was further attributed to double layer capacitance ( C dl ), which indefinitely divulged the inferiority of NiCo 2 O 4 compared to Ni 2.5 Co 5 C 2 O 4 for the alkaline oxygen evolution reaction (OER). The obtained proton reaction order ( ρ RHE ) was about 0.80, thus indicating the proton decoupled electron transfer (PDET) mechanism for OER in alkaline medium. Post-catalytic investigation revealed the formation of a flake-like porous nanostructure, indicating distinct transformation in morphology during the alkaline OER process. Further, XPS analysis demonstrated complete oxidation of Ni 2+ and Co 2+ centres into Ni 3+ and Co 3+ , respectively under high oxidation potential, thereby indicating active site formation throughout the microstructural network. Additionally, from BET-normalised LSV investigation, the intrinsic activity of Ni 2.5 Co 5 C 2 O 4 was also found to be higher than that of NiCo 2 O 4 . Finally, Ni 2.5 Co 5 C 2 O 4 delivered a TOF value of around 3.28 × 10 -3 s -1 , which is 5.56 fold that of NiCo 2 O 4 for the alkaline OER process. This report highlights the unique benefit of Ni 2.5 Co 5 C 2 O 4 over NiCo 2 O 4 for the alkaline OER. The structure-catalytic property relationship was further elucidated using density functional theory (DFT) study. To the best of our knowledge, nickel-cobalt oxalate (Ni 2.5 Co 5 C 2 O 4 ) was introduced for the first time as a non-precious non-oxide electrocatalyst for alkaline OER application.