Strategic Synthesis of Heptacoordinated Fe^III Bifunctional Complexes for Efficient Water Electrolysis

Abstract In this research, highly efficient heterogeneous bifunctional (BF) electrocatalysts (ECs) have been strategically designed by Fe coordination (C R ) complexes, [Fe 2 L 2 (H 2 O) 2 Cl 2 ] (C1) and [Fe 2 L 2 (H 2 O) 2 (SO 4 )].2(CH 4 O) (C2) where the high seven C R number synergistically modifies the electronic environment of the Fe centre for facilitation of H 2 O electrolysis. The electronic status of Fe and its adjacent atomic sites have been further modified by the replacement of −Cl − in C1 by −SO 4 2− in C2 . Interestingly, compared to C1 , the O−S−O bridged C2 reveals superior BF activity with extremely low overpotential (η) at 10 mA cm −2 (140 mV OER , 62 mV HER ) and small Tafel slope (120.9 mV dec −1 OER , 45.8 mV dec −1 HER ). Additionally, C2 also facilitates a high‐performance alkaline H 2 O 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.