Isolation of a Bridging Phosphide-Supported Redox-Active Neutral Ag4-Nanocluster as a Molecular Energy Storage Material.

Stabilization of robust and structurally well-defined AgI-based nanoclusters as molecular pseudocapacitors for electrochemical energy storage has been unexplored. Herein, we report on the novel synthesis, solid-state isolation, and pseudocapacitor studies of an atomically precise neutral redox-active Ag4 nanocluster [((Cy-cAI)P(Dipp))4Ag4] (2), supported by the unique bulky μ2-phosphide ligands. Cyclic voltammetry (CV) studies on 2 revealed a possible quasi-reversible one-electron reduction, suggesting in situ generation of the corresponding radical anion 2·-, which was further supported by the electron paramagnetic resonance (EPR) spectroscopy and Mulliken spin density calculations. The unprecedented effort to fabricate an electrode by depositing 2 on a solid support, investigating the pseudocapacitive behavior in a 1 M NaClO4 electrolyte by employing a three-electrode cell arrangement, was successful. The corresponding CV profiles exhibited a quasi-rectangular profile with redox peaks, signifying a combination of electric double-layer capacitive (EDLC) and pseudocapacitive effects with the highest specific capacitance value of 168.9 F g-1 (185.8 mF cm-2) at a 2 mV s-1 scan rate.