Carbon quantum dot-mediated synergistic regulation of charge transport, redox activity, and interfacial electrochemical kinetics toward high-performance NiO/WO3 complementary electrochromic devices

Nickel oxide (NiO), as a typical anodic electrochromic material, has been widely employed in complementary electrochromic devices (CECDs) with tungsten oxide (WO 3 ) because of its excellent charge compensation capability and reversible redox behavior. However, its poor electrical conductivity and sluggish ion diffusion kinetics hinder further improvements in electrochromic performance. In this work, carbon quantum dots (CQDs) were introduced into the NiO electrochromic system to fabricate NiO/CQDs composite films, and the regulatory mechanism of CQDs on the electrochromic behavior of NiO was systematically investigated. The results demonstrate that the incorporation of CQDs preserves the intrinsic crystal structure of NiO while significantly improving its interfacial electrochemical properties. Specifically, CQDs reduce the charge-transfer resistance, accelerate electron transport, enhance redox activity and charge storage capability, promote Li + diffusion, and improve electrochemical reaction kinetics. Moreover, the increased proportion of electrochemically active Ni 3+ species enhances the pseudocapacitive behavior of NiO. Benefiting from these synergistic effects, the NiO/CQDs composite film exhibits a 20% increase in optical modulation, 53%/10% faster coloration/bleaching response, and a 28% improvement in cycling stability compared with pristine NiO. Furthermore, the assembled WO 3 -NiO CECD delivers an areal charge capacity of 58.75 mC cm −2 , a coloration efficiency of 157.72 cm 2  C −1 , rapid response times of 2.7 s/1.6 s, and superior cycling stability. This work elucidates the enhancement mechanism of CQDs from the perspectives of electron transport, Ni valence regulation, and ion diffusion kinetics, providing a theoretical basis for the design of high-performance CECDs.