Integrated emergy and exergy research through co-citation analysis: Knowledge bases, evolutionary trajectories and frontier frameworks

The integrated research of emergy and exergy has promoted the innovation and development of eco-thermodynamics and eco-economics. The aim of this study is to investigate the research hotspots, frontiers, evolution paths, and inflection points of the integrated studies on emergy and exergy, by using a bibliometric approach and the database of Web of Science (WoS) (1995-2025). The results reveal the following: (1) six interlinked knowledge bases, i.e., ecological thermodynamic accounting, advanced energy systems, hybrid LCA–emergy frameworks, wetland eco-engineering, industrial metabolism, and marine natural capital assessment constitute the theoretical pillars of the field; (2) research content evolves along four nested application layers (process, system, regional, global) and has matured through three stages: theoretical foundation (pre-2005), methodological diffusion (2006–2015), and integrative deepening (2016–2025); and (3) current frontiers concentrate on standardizing global emergy baselines, coupling cosmic-exergy-based ecological footprint models, and translating emergy/exergy ratios into actionable metrics for carbon neutrality and circular-economy policies. A framework is constructed to describe the system of current related research to provide a reference for scholars to carry out targeted research.