Nickel Oxide Films with Superior Electrochromic Performance Reinforced by Graphene Quantum Dots

Abstract Nickel oxide (NiO) is considered as an ideal counter electrode to build complementary electrochromic devices with tungsten oxide (WO ₃ ) due to charge balance, and complementary color modulation. However, currently reported NiO films exhibit poor electrochromic properties in LiClO ₄ /PC electrolytes due to poor conductivity and Li ⁺ trapping. Here, a novel strategy is exploited to enhance the electrochromic properties of NiO films in LiClO ₄ /PC based on graphene quantum dots (GQDs). GQDs with uniform particle size and rich surface functional groups are prepared by cracking carbon nanotubes with HNO ₃ , and then GQDs/NiO composite films are synthesized through chemical bath deposition. The strong interface bonding between GQDs and NiO allows for the efficient promotion of charge transfer and Li ⁺ diffusion with larger surface potential difference, and alleviate stress produced during the electrochromic reaction. GQDs‐2/NiO demonstrate outstanding electrochromic performance in LiClO ₄ /PC with wider optical modulation (ΔT of 56%), faster switching speed (τ _c /τ _b = 3.7/2.4 s), and better cycle stability (5000 cycles) than that of pure NiO. Besides, the electrochromic devices assembled by GQDs‐2/NiO display excellent electrochromic performances. This study provides innovative guidance for the preparation of NiO films with excellent electrochromic properties in LiClO ₄ /PC electrolytes, and pioneers new route for expanding the optoelectronic applications of GQDs.