Electrochromic (EC) smart windows are promising for dynamic solar energy management, and aqueous alkaline electrolytes offer advantages such as low cost, safety, and environmental compatibility. However, their application is limited by the chemical instability of conventional tungsten-based materials such as WO₃ under hydroxide-rich conditions. Here, we report an alkaline-compatible complementary EC system based on Nb₁₈W₁₆O₉₃/NiHPO₄ electrodes that operate via a K⁺/OH^- co-intercalation mechanism in an aqueous KOH electrolyte. Nb₁₈W₁₆O₉₃ enables reversible tungsten-based electrochromism under alkaline conditions, overcoming the intrinsic limitation of WO₃, while NiHPO₄ provides a high-efficiency anodic counterpart with complementary electrochemical kinetics. The assembled device exhibits broadband modulation across the visible and near-infrared regions, achieving transmittance modulation of 43.7% at 630 nm and 20.4% at 1200 nm with coloration efficiencies of 74.6 and 79.1 cm²/C. This broadband optical response enables effective solar thermal regulation, attenuating 75.2% of incident solar energy (350-1200 nm) and reducing the surface temperature by approximately 14 °C under AM 1.5G illumination. Furthermore, the device maintains uniform EC performance upon scaling to 25 cm², demonstrating the feasibility of the K⁺/OH^- co-intercalation configuration for large-area alkaline EC devices. These results establish Nb₁₈W₁₆O₉₃ as a viable alkaline-compatible cathodic EC material and provide a practical strategy for complementary EC smart windows capable of broadband solar modulation and dynamic heat regulation in aqueous alkaline electrolytes.
Electrochromic (EC) smart windows are promising for dynamic solar energy management, and aqueous alkaline electrolytes offer advantages such as low cost, safety, and environmental compatibility. However, their application is limited by the chemical instability of conventional tungsten-based materials such as WO₃ under hydroxide-rich conditions. Here, we report an alkaline-compatible complementary EC system based on Nb₁₈W₁₆O₉₃/NiHPO₄ electrodes that operate via a K⁺/OH^- co-intercalation mechanism in an aqueous KOH electrolyte. Nb₁₈W₁₆O₉₃ enables reversible tungsten-based electrochromism under alkaline conditions, overcoming the intrinsic limitation of WO₃, while NiHPO₄ provides a high-efficiency anodic counterpart with complementary electrochemical kinetics. The assembled device exhibits broadband modulation across the visible and near-infrared regions, achieving transmittance modulation of 43.7% at 630 nm and 20.4% at 1200 nm with coloration efficiencies of 74.6 and 79.1 cm²/C. This broadband optical response enables effective solar thermal regulation, attenuating 75.2% of incident solar energy (350-1200 nm) and reducing the surface temperature by approximately 14 °C under AM 1.5G illumination. Furthermore, the device maintains uniform EC performance upon scaling to 25 cm², demonstrating the feasibility of the K⁺/OH^- co-intercalation configuration for large-area alkaline EC devices. These results establish Nb₁₈W₁₆O₉₃ as a viable alkaline-compatible cathodic EC material and provide a practical strategy for complementary EC smart windows capable of broadband solar modulation and dynamic heat regulation in aqueous alkaline electrolytes.

Electrochromic device,Niobium tungsten oxide,Nickel hydrogen phosphate,Alkaline electrolyte,Solar heat regulation