Enhancing Oxygen Reduction Reaction Through Ligand Modulation in Copper(II) Phosphinate Complexes

Abstract The development of copper complexes for electrocatalytic oxygen reduction is crucial for advancing renewable energy technologies. Herein, we report the synthesis of two new copper phosphinate complexes, [Cu(H 2 L 1 ) 2 (py‐tpy)] n (1) and [Cu(H 2 L 1 ) 2 (Cl‐tpy)] (2), where py‐tpy = 4′‐pyridyl‐2,2′:6′,2′′‐terpyridine and Cl‐tpy = 4ʹ‐chloro‐2,2ʹ:6ʹ,2ʹʹ‐terpyridine serve as ancillary nitrogen‐donor ligands. Complexes 1 and 2 were isolated as single crystals and characterized by spectroscopic and microanalytical techniques. Electrochemical studies in O 2 ‐saturated PBS (0.1 M, pH 7.2) revealed that complex 1 has a more positive ORR onset potential (0.45 V), indicating improved catalytic kinetics. RRDE experiments further demonstrated its higher selectivity for the four‐electron reduction pathway (∼3.95), effectively minimizing hydrogen peroxide formation. RRDE measurements indicated n ≈ 3.95 and low H 2 O 2 yields of about 2 percent, determined electrochemically, while chemical iodometric quantification was below the detection limit. To ensure stability and durability of the catalysts, chronoamperometry was performed over 8 h in an oxygen environment. Magnetic properties of complexes 1 and 2 were investigated through magnetic susceptibility measurements on polycrystalline samples, hinting at the weak ferromagnetic interactions at higher temperatures. This study highlights the potential of copper phosphinate complexes as promising electrocatalysts for ORR, providing insights into their structure‐activity relationships. These findings contribute to the ongoing search for efficient, earth‐abundant catalysts for energy conversion applications.