De Novo Dodecanuclear Iron(III/IV)-Based Molecular Wheel-Derived Heteronanocomposite as a Cost-Effective and High-Performance Bifunctional Electrocatalyst for Water Splitting

In pursuing carbon-free renewable energy sustainability, the development of cost-effective and high-performance transition metal-based electrocatalysts holds great promise for improved water splitting. In this context, relatively unexplored high-nuclear-cluster-derived robust electrocatalysts with more accessible and active catalytic sites present an emerging prospect. In this work, we report the synthesis of a heterovalent molecular wheel, [Fe 12 (μ 3 -O) 8 (μ 2 -O) 4 (OH) 4 (OAc) 16 ] ( [Fe 12 O 12 ] ), used as a sacrificial template to derive Fe 2 O 3 /MoO 2 heteronanocomposite, denoted as [Fe 12 O 12 ]@Fe 2 O 3 /MoO 2 through calcination at 600 °C. Crystal structure analysis reveals that the molecular wheel-shaped dodecanuclear iron cluster crystallizes in a tetragonal lattice with I -4 space group comprising 8Fe 3+ and an unprecedented 4Fe 4+ ions, as consolidated by XPS analysis and BVS calculation. [Fe 12 O 12 ]@Fe 2 O 3 /MoO 2 with a high electrochemical surface area (423.33 cm 2 ) exhibits outstanding bifunctional electrocatalytic activity, requiring low overpotentials of 149 mV for the HER and 298 mV for the OER to generate 10 mA/cm 2 current density in 1 M KOH, and excellent stability over 50 h. The enhanced catalytic efficiency of [Fe 12 O 12 ]@Fe 2 O 3 /MoO 2 on nickel foam (NF) for water splitting arises from the strong synergistic interaction between Fe 3+, Mo 4+ along with Ni 2+ sites, precisely balancing OH*/H* adsorption, and improved electrocatalytic water dissociation with an overall cell voltage of 1.72 V. To our knowledge, this work is the first report where a discrete iron-based molecular wheel is successfully employed as a precursor to develop a nanoelectrocatalyst for bifunctional water splitting in alkaline media.