The effect of organic ligand skeletons of 2D π–d conjugated metal–organic frameworks on their OER performance and stability

Abstract

Two-dimensional π–d conjugated metal–organic frameworks (2D cMOFs) exhibit great potential in electrocatalysis due to their high conductivity. However, how to further improve the electrocatalytic activity and stability of 2D cMOFs remains a significant challenge. Therefore, this study systematically investigated the impact of ligand skeletons of 2D cMOFs on their electrocatalytic activity and stability. In this study, two bimetallic 2D cMOFs FeCoTHT (THT = 2,3,6,7,10,11-triphenylenehexathiol) and FeCoBHT (BHT = 1,2,3,4,5,6-benzenehexathiol) with identical Fe and Co metal ratios were synthesized through using different lengths of organic ligand skeletons with the same functional groups. Interestingly, FeCoTHT with a longer organic skeleton displays superior oxygen evolution reaction (OER) activity (253 mV at 10 mA cm⁻²) compared to FeCoBHT (298 mV at 10 mA cm⁻²). Density functional theory (DFT) calculations indicate that different ligand skeletons of 2D cMOFs would affect their d-band center energy (E_d) level and electronic structure. When THT is used as the organic ligand, the d-band center energy (E_d) level shifts closer to the Fermi level than that of BHT, thereby optimizing the adsorption of reaction intermediates and effectively improving the OER catalytic performance. Meanwhile, FeCoTHT also exhibits enhanced stability relative to FeCoBHT. In situ Raman spectra further indicate that FeCoBHT undergoes a structural reconstruction during the OER process, whereas FeCoTHT maintains its structural integrity. DFT calculations further validate the superior OER activity and high structural stability of FeCoTHT than those of FeCoBHT theoretically. This study provides a new insight into the influence of organic ligand variations on the electrocatalytic activity and stability of 2D cMOFs.