• Pt-loaded nanoporous GaN enables room-temperature NO2 sensing with high sensitivity (200 ppm to 100 ppb) and fast response (22 s) and recovery (170 s).
• The sensor exhibits excellent selectivity for NO2 over other gases, attributed to the spillover effect and electronic interaction of Pt.
• The low detection limit of 100 ppb and stability over 70 days highlight its practical potential for environmental and health monitoring.
• The gas-sensing mechanism is clarified, emphasizing the role of Pt in enhancing electron donation and oxygen dissociation.