Clean energy technology collaboration and urban carbon intensity: Regional heterogeneity and spatial spillover...

Clean energy technology (CET) collaboration serves as an important mechanism for promoting clean technology diffusion and supporting reductions in urban carbon intensity. However, existing studies have rarely distinguished the heterogeneous effects of different collaboration dimensions or examined how their spillovers vary across space. To address these gaps, this study uses patent collaboration data covering 41 cities in the Yangtze River Delta from 2010 to 2023 and measures CET collaboration across three dimensions: collaboration density, collaboration intensity, and collaboration breadth. Spatial econometric models are employed to examine their nonlinear effects on urban carbon emission intensity, regional heterogeneity, and distance-bounded spillover patterns. The results show that all three collaboration dimensions exhibit nonlinear threshold effects on carbon intensity, but their impacts differ across core, central, and peripheral areas. Collaboration intensity and breadth generate positive environmental spillovers by reducing carbon intensity in neighboring cities, whereas excessive local collaboration density may produce a siphoning effect. Distance-band analysis further reveals that CET collaboration spillovers are not simply monotonic but display bounded and non-linear spatial effects, with stronger mitigation effects around 200 km and 400-500 km. This study contributes to the literature by integrating multidimensional collaboration, intra-agglomeration heterogeneity, and spatial spillover boundaries into a unified framework, providing evidence for differentiated regional innovation and carbon-reduction policies.