Five novel MOFs with various dimensions as efficient catalysts for oxygen evolution reactions

Abstract

Five novel metal–organic frameworks (MOFs) with the formula [M^II(dcpbpy)(sol)_x]_n (M^II = Co^II, sol = H₂O, x = 1, 1; M^II = Ni^II, sol = H₂O, x = 1, 2; M^II = Mn^II, sol = DMAc, x = 1, 3; M^II = Mn^II, sol = DMF, x = 1, 4; M^II = Mn^II, sol = H₂O, x = 2, 5; dcpbpy = 4-(2,4-dicarboxylphenyl)-4,2′:6′,4′′-terpyridine) having various dimensions were prepared with different solvents and transition-metal ions (Co^II, Ni^II and Mn^II). Single-crystal X-ray diffraction showed that 1–5 resulted in the grid layer stacked 3D (1 and 2), 2D (3 and 4) and 1D (5) frame structures due to their different coordination modes. Electrochemical analyses showed that 1–5 displayed efficient catalytic activity towards oxygen evolution reactions (OERs) under alkaline conditions. Besides, 1–2 with the stacked 3D framework could present a large interaction and result in a low overpotential of their OER behaviour, compared to the 2D (3 and 4) and 1D (5) frameworks. MOF 2 with a 3D frame structure and Ni^II as the active central ion gave the lowest required overpotential (130 mV) to generate a current density of 1 mA cm⁻².