Strategic Synthesis of Heptacoordinated FeIII Bifunctional Complexes for Efficient Water Electrolysis

In this research, highly efficient heterogeneous bifunctional (BF) electrocatalysts (ECs) have been strategically designed by Fe coordination (C-R) complexes, [Fe2L2(H2O)(2)Cl-2] (C1) and [Fe2L2(H2O)(2)(SO4)].2(CH4O) (C2) where the high seven C-R number synergistically modifies the electronic environment of the Fe centre for facilitation of H2O electrolysis. The electronic status of Fe and its adjacent atomic sites have been further modified by the replacement of -Cl- in C1 by -SO42- in C2. Interestingly, compared to C1, the O-S-O bridged C2 reveals superior BF activity with extremely low overpotential (& eta;) at 10 mA cm(-2) (140 mV(OER), 62 mV(HER)) and small Tafel slope (120.9 mV dec(OER)(-1), 45.8 mV dec(HER)(-1)). Additionally, C2 also facilitates a high-performance alkaline H2O electrolyzer with cell voltage of 1.54 V at 10 mA cm(-2) and exhibits remarkable long-term stability. Thus, exploration of the intrinsic properties of metal-organic framework (MOF)-based ECs opens up a new approach to the rational design of a wide range of molecular catalysts.