Metal metaphosphate complexes for redox flow batteries

Abstract

In this thesis, possibility of using anionic metal complexes to limit crossover of active species in redox flow batteries was explored. A series of first row transition metal trimetaphosphate complexes as bis(triphenylphosphine)iminium (PPN) salts have been prepared. Their electrochemical properties have been studied to evaluate them for redox flow battery applications. [PPN]₃[Fe(P₃Og)₂] and [PPN]₂[VO(P₃O₉)(acac)] were identified as a suitable couple for a dual-active-species redox flow battery with an open cell potential of 1.5 V. [PPN]₃[V(P₃Og)₂] can be oxidized and reduced within the stability window of acetonitrile and it is therefor a promising candidate for single-active-species redox flow battery applications. The difference in redox potentials between the V(III)/V(IV) and V(II)/V(III) couples is 2.7 V which is the highest peak to peak separation reported in the literature to date.