Computational Design of 1D MOFs as Tunable Single-Atom Catalysts for Water Splitting Reaction

Traditional catalysts used for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) associated with water splitting reaction have faced backlash due to their higher cost and scarcity. Therefore, in an effort to compete with increasing energy requirements, identifying inexpensive and efficient catalysts is highly important. In this work, using the periodic density functional theory studies, transition metal (TM)-based 1D-coordination polymers composed of TM (Co, Ni, Cu, and Zn) and benzene-tetraamine (BTA) have been explored as efficient catalysts for both OER and HER. Among Co–, Ni–, Cu–, and Zn–BTA systems considered, Co–BTA is found to be the most efficient catalyst for OER with a calculated overpotential value of 0.25 V. Further, to fine-tune the catalytic activity through modulating the electronic structure of the active sites, functionalization of Co–N4 units by phenyl (electron withdrawing) and methyl (electron donating) groups is studied. It is observed that the phenyl-functionalized Co–BTA shows enhanced catalytic activity for the OER with an overpotential value of 0.16 V. Functionalization with an electron-donating substituent (methyl) is found to significantly enhance the HER activity with a 10 times lower free-energy change for H adsorption as compared to that in pure Co–BTA. The results obtained are explained using the calculated Bader charges on the metal atom and interaction energies of various intermediate species with the active site of the catalyst. The effect of the solvent on the calculated overpotential is explored by considering explicit solvent molecules around the active sites. These results can provide valuable insights into developing efficient noble metal-free catalysts for the OER and HER.