Self-nucleation growth of bimetallic niobium tungsten oxide electrodes with delaminated nanostructure for excellent dual-band electrochromic performance

Abstract

Dual-band electrochromic (EC) smart windows, dynamically and independently controlling the transmittance of near-infrared (NIR) and visible (VIS) light, can significantly reduce the energy consumption of buildings. Here, we provide a self-nucleation solvothermal strategy to prepare nanostructured bimetallic niobium tungsten oxide (Nb₁₈W₁₆O₉₃, NWO) on FTO substrates featuring a delaminated manner with a bush-like morphology composed of nanoneedles as the upper layer and a dense structure comprising nanoparticles as the down layer. Such structure combines good adhesion to the substrate and great electrochemical activity, leading to excellent dual-band electrochromic properties, including large optical modulation (72.6 % at 633 nm and 86.6 % at 1600 nm), high color rendering efficiencies (41.9 cm²/C at 633 nm and 53.2 cm²/C at 1600 nm), and long cyclic stability (retaining 85.4 % at 633 nm and nearly 100 % at 1600 nm after 1500 cycles). The as-prepared NWO electrode achieves three types of electrochromic effects: bright, cold, and dark electrochromic modes corresponding to the different threshold potentials of W and Nb elements during the electrochromic process. These results demonstrate that the nanostructured Nb₁₈W₁₆O₉₃ has promising performance as smart window electrodes in energy-saving buildings and propose a one-step template-free way to synthesize films with complex nanostructures.