This study explores the optimization of metal–organic frameworks (MOFs) for enhancing oxygen evolution reaction (OER) activity through bond length adjustment. The researchers developed a method to acid etch Co-naphthalenedicarboxylic acid-based MOFs (AE-CoNDA) to optimize the bond length, which in turn regulates the spin state transition at the Co active sites. The AE-CoNDA catalyst exhibited excellent OER activity with a low overpotential of 260 mV to reach 10 mA cm−2 and a small Tafel slope of 62 mV dec−1. When integrated into BiVO4, the AE-CoNDA cocatalyst significantly improved the photocurrent density to 4.3 mA cm−2 at 1.23 V under AM 1.5G irradiation. The stretched Co–O bond length was found to optimize the orbital hybridization of Co 3d and O 2p, enhancing the adsorption of oxygen-containing intermediates and accelerating the OER kinetics. Theoretical calculations confirmed that the high spin state of Co sites facilitated the reaction by strengthening the interaction between Co active sites and oxygen-containing intermediates. This work demonstrates a novel approach to enhancing the catalytic activity of MOFs for water splitting applications.This study explores the optimization of metal–organic frameworks (MOFs) for enhancing oxygen evolution reaction (OER) activity through bond length adjustment. The researchers developed a method to acid etch Co-naphthalenedicarboxylic acid-based MOFs (AE-CoNDA) to optimize the bond length, which in turn regulates the spin state transition at the Co active sites. The AE-CoNDA catalyst exhibited excellent OER activity with a low overpotential of 260 mV to reach 10 mA cm−2 and a small Tafel slope of 62 mV dec−1. When integrated into BiVO4, the AE-CoNDA cocatalyst significantly improved the photocurrent density to 4.3 mA cm−2 at 1.23 V under AM 1.5G irradiation. The stretched Co–O bond length was found to optimize the orbital hybridization of Co 3d and O 2p, enhancing the adsorption of oxygen-containing intermediates and accelerating the OER kinetics. Theoretical calculations confirmed that the high spin state of Co sites facilitated the reaction by strengthening the interaction between Co active sites and oxygen-containing intermediates. This work demonstrates a novel approach to enhancing the catalytic activity of MOFs for water splitting applications.