Super-reduced Polyoxometalates in Aqueous Solution: Historical Perspectives and Current Challenges

Abstract

Polyoxometalates (POMs) represent a versatile class of molecular metal oxides often described as “electron reservoir” or “electron sponge” due to their remarkable ability to store and transfer electrons. These properties make them highly attractive for applications in electrochemical-energy storage systems, such as batteries or supercapacitors. This contribution reports the historical milestones and modern advancements of the super-reduced POMs in aqueous solution, focusing on systems constructed from molybdenum and tungsten centers. Particular attention is given to the pioneering work of Souchay and his students, who, between the 1960s and 1980s, published a series of articles (originally in French) that highlighted the exceptional super-reducibility of Keggin-type POMs. The aim of this work is to guide researchers interested in using POMs for electrochemical energy storage applications, and to identify future challenges in the chemistry of super-reduced POMs.