Dynamic coordination transformation of active sites in single-atom MoS₂ catalysts for boosted oxygen evolution catalysis

The development of low-cost and efficient electrocatalysts for the oxygen evolution reaction (OER) is critical for enhancing the efficiency of the water-splitting reaction. Although MoS₂ is a promising hydrogen evolution electrocatalyst, its oxygen evolution activity is significantly poor due to its weak adsorption for oxidative intermediates such as OH* and OOH*. Here, we present a strategy for designing 3d-TM-O_x (x = 3, 6; TM: transition metal) single-atom catalytic sites to achieve high catalytic activity towards the OER through an unprecedented dynamic coordination transformation from [TMO₆] to [TMO₃]. By using first-principles calculations and molecular dynamic simulations, we predict single 3d-transition metal atoms (3d-TM) co-doped with six oxygen atoms of MoS₂ (3d-TMO₆@MoS₂) with hexa-coordinated TM (TM = Sc, Ti, V, Cr, Mn, Fe and Co) and tri-coordinated TM (TM = Ni, Cu and Zn) structures. Our calculations show that these hexa-coordinated TMs are induced to transform into a tetra-coordinated structure as oxidative intermediates approach. The dynamic single-atom catalytic mechanism makes active sites and adsorption-responsive orbitals exposed, which is favorable to strengthen the adsorption of oxidative intermediates and improve the OER catalytic activity. Comparative calculations demonstrate that TMO₆@MoS₂ (TM = Fe, Mn and Co) species render better electrocatalytic activity for the OER than benchmark IrO₂. Experimental Raman studies verified that FeO₆@MoS₂ experiences coordination transformation from [TMO₆] to [TMO₃] during the OER process. The low overpotential of 0.18 V at a current density of 10 mA cm⁻² and good structural stability are consistent with our computational prediction. The present study sheds light on deep understanding of single-atom catalytic structures in transition metal dichalcogenides and the methodology to tune the catalytic activity of single-atom sites.