A Narrative Review of Four-Membered Heterocycles in Next-Generation Energy Conversion and Storage

Abstract

This narrative review critically examines the emerging and potential applications of four-membered heterocyclic compounds, specifically azetidines, oxetanes, thietanes, and phosphetanes, in the rapidly evolving field of energy conversion and storage technologies. We provide a focused analysis of their unique structural features, inherent ring strain, electronic properties, and functional versatility that make them intriguing candidates for advanced energy materials. The discussion highlights key research questions and the methodologies being employed to address them. Oxetanes have demonstrated notable success in organic photovoltaics (OPVs), where their incorporation, often via cross-linking strategies, has led to documented enhancements in light absorption, charge transport, morphological stability, and overall device longevity, contributing to improved power conversion efficiencies. In contrast, the exploration of thietanes and phosphetanes in battery technologies, particularly for stabilizing electrolytes in lithium–sulfur (Li–S) batteries or as components in solid-state electrolytes, remains largely developmental but holds significant promise for improving ionic conductivity, interfacial stability, and cycle life. Similarly, azetidines are considered potential candidates for proton exchange membranes (PEMs) in fuel cells, potentially offering enhanced proton conductivity and thermal stability, although experimental validation is less advanced. This narrative review synthesizes current knowledge, underscores the critical research gaps, particularly the need for more experimental validation for battery and fuel cell applications, and discusses functionalization strategies and computational modeling efforts aimed at optimizing performance. By comparing the distinct roles and potentials of these heterocycles across different energy systems and outlining future research directions, this work aims to provide a valuable roadmap for unlocking the full potential of strained four-membered rings in next-generation energy technologies, highlighting the novelty of consolidating this specific chemical class within the broad energy landscape.