Digital Finance, Regional Infrastructure, and Urban Carbon-Emission Efficiency: A Spatial Nonlinear Analysis Based on the New Western Land–Sea Corridor

Against the backdrop of China’s “dual-carbon” targets and the digital era, examining how digital finance (DF) in the New Western Land–Sea Corridor (NWLSC) shapes urban carbon-emission efficiency (CEE) is pivotal for fostering high-quality economic development and advancing the large-scale development of western China. Building on a theoretical exposition of how DF influences urban CEE, we empirically investigate both the direction and the underlying mechanisms of this influence by applying fixed-effects and spatial-panel smooth-transition regression models to panel data covering 88 cities in the NWLSC from 2011 to 2022. The results reveal the following: (1) The direct impact of DF on urban CEE in the NWLSC follows a nonlinear inhibitory effect, which gradually weakens with the increase in DF. (2) The influence of DF on urban CEE exhibits pronounced heterogeneity across NWLSC regions over time and at different quantiles. (3) As transportation and information infrastructures improve incrementally, the effect of DF on local CEE traces a nonlinear inhibitory effect and has a nonlinear spillover effect on neighboring cities’ CEE. These findings imply that policymakers along the corridor should accelerate the development of DF and foster its organic integration with transportation and information infrastructures, so as to advance the high-quality construction of the NWLSC and, ultimately, China’s high-quality economic growth through regionally coordinated and context-specific strategies.