Energy storage is a vital aspect for the successful implementation of renewable energy resources on a global scale. Herein, we investigated the redox cycle of nickel dithiocarbamates for potential use as catholytes in non-aqueous redox flow batteries. The unique redox cycle of nickel dithiocarbamates (Ni(dtc)2) offers the ability to better understand these reactions by displaying 2e- chemistry upon oxidation from Ni(II) → Ni(IV) but 1e- chemistry upon reduction from Ni(IV) → Ni(III) → Ni(II). The underlying reasons for this cycle lie in the structural changes that occur between four-coordinate Ni(dtc)2 and six-coordinate [Ni(dtc)3]+. Cyclic voltammetry and spectroscopic experiments show that these 1e- and 2e- pathways can be controlled by the addition of ancillary ligands such as pyridine derivatives and Lewis acids such as Zn(II). Specifically, the addition of Zn(II) to the electrolyte is shown to consolidate the two 1e- reduction peaks into a single 2e- reduction where [Ni(dtc)3]+ is reduced directly to Ni(dtc)2. This enhancement is believed to be due to chemical assistance in removing a dtc- ligand from a Ni(dtc)3 intermediate, allowing for easier reduction to Ni(dtc)2. Around 96% columbic efficiency obtained when Ni(dtc)2 was used as catholyte in the chrono potentiometric (CP) H cell experiment in presence of 24 mM Zn2+ ion.

Two one electron vs one two-electron redox system of nickel diethyldithiocarbamate for redox flow battery

ACS Fall 2021

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