Thermal Fingerprints of the Oxygen Evolution Reaction: Mechanistic and Kinetic Study across a Heteroatom-Based Bimetallic Metal–Organic Framework Family

Tuning local reaction, ligand, and metal node environment is an important and challenging issue for enhancing the electrochemical oxygen evolution reaction performance. Herein, we propose a strategy of engineering the bimetallic MOF structures via tuning the Co content at the peripheral sites of the 2D heteroatom-based dicarboxylic ligand structures. The successful creation of bimetallic MOF units up to a certain metal ratio is isostructural, and thereafter, at higher content of Co, the appearance of new phases in the system occurs. This tuning of metal ratio provides a conducive atmosphere for tuning high electrocatalytic interface OER activity under alkaline medium. We observed onset potentials of 1.49 and 1.55 V vs RHE for S- and N-containing MOFs, with Tafel slopes of ∼76 and ∼118 mV dec–1 and the TOF of ∼0.38 and ∼0.365 s–1,respectively. The temperature dependence of this reaction was also carried out to extract the kinetic parameters obtained from the temperature-dependent Arrhenius equation. A linear relationship of Tafel slopes with temperature and activation energy with overpotential was found. Standard activation energies of ∼14.3 and ∼31.7 kJ/mol in cases of S- and N-based MOF, respectively, with the metal ratio of Ni1Co3 were found. The mechanistic study via DFT infers that the introduction of Co content in each MOF unit weakens the Ni–O bonding character, thereby enhancing the radical characteristics of the bridging oxo and enhancing the OER activity. The overall Gibbs free energy for the splitting was found to be −3.71 eV or −357.96 kJ mol–1 for Ni1Co3(TDC) MOF and −2.55 eV or −246.04 kJ mol–1 for Ni1Co3(PDC) MOF. These findings provide first temperature-dependent insights into the behavior of MOFs toward OER catalysis at elevated temperatures, which are of great importance for industrial applications.