Xenes for Sustainable Energy: A Roadmap From First‐Principles Design to Practical Deployment

The rapid transition toward sustainable energy systems requires advanced materials for efficient energy storage and conversion. Although graphene and MXenes have dominated two‐dimensional (2D) materials research, their practical deployment remains limited by stability, reproducibility, and integration challenges. Emerging 2D materials, including borophene, phosphorene, antimonene, tellurene, and silicene, offer distinctive electronic structures, anisotropic charge transport, and tunable surface chemistries. Theoretical studies predict exceptional performance in batteries, supercapacitors, metal‐air systems, electrocatalysis, CO 2 reduction, photocatalysis, and thermoelectrics; however, experimental outcomes often remain below expectations due to chemical instability, synthesis variability, and interfacial degradation. This review critically examines these theory–experiment discrepancies by comparing computational predictions with experimental results and identifying unresolved challenges in stability, reproducibility, and benchmarking. It further highlights defect and vacancy engineering, heterostructure assembly, doping, and interface stabilization as key strategies for improving practical performance. Finally, a forward‐looking roadmap is proposed that integrates nanoscale material design, scalable processing, standardized evaluation, and emerging data‐driven approaches to support the translation of emerging 2D materials into sustainable energy‐storage and conversion technologies.