Polyoxometalates(POMs) as Proton Conductors

The development of solid-state proton conductors (SSPCs) is of significant interest for their deployment as proton exchange membranes in fuel cell (PEMFC) technology. The <i>aqueous medium</i> synthesis with ample <i>intrinsic</i> proton sources has made crystalline polyoxometalates (POMs) promising SSPCs over others. Herein, we aim to showcase the solitary POMs and their hybrids (with polymers and MOFs/COFs) as SSPCs by organizing them based on the approaches taken up (<i>intrinsic</i> or <i>extrinsic</i>) to install various protonic sources while positioning them within specific components of the POM frameworks. Particular attention is paid with a critical discussion on whether the conductivity is purely protonic or a combination of protonic and other ionic conductivity (majorly originating from charge balancing counterions) and thus recommend the terminology to be used. The “Critical Discussion” section provides in-depth insights which are often overlooked, while the future recommendations are made in “Future Outlook”.