Even though electrochromism has been around for more than 50 years, it still has several issues. Multi-layered films, high manufacturing costs, and a short lifetime are present in existing electrochromic devices. We demonstrate a unique high-performance device with a basic structure and no solid electrochromic sheets in this work. In this device, the electrolyte layer is also avoided. The device uses an electrochromic solution prepared from a mixture of ammonium metatungstate and iron (II) chloride solution as a functional layer with reversible redox properties. The tungstate ions on the electrode surface are reduced when the device is colored, and the Fe2+ on the electrode surface is oxidized on another electrode surface. The generated Fe3+ in the mixed functional layer oxidizes the previously reduced tungstate ions as the device fades. We determined the ΔT (transmittance modulation) and response time among ammonium metatungstate ratios, iron (II) chloride ratios, and driven current density using DOE (design of experiment) trials. Using 0.175 mol/L ammonium metatungstate and 0.30 mol/L iron (II) chloride, a device with outstanding ΔT (more than 57% at 700 nm), a short response time (less than 10 s), and high coloring efficiency (160.04 cm2/C at 700 nm) is demonstrated.

The Graphene@PtSe2 heterostructure is an excellent long-wave infrared detection material. However, the expensive cost of PtSe2 prevents its widespread use in infrared detection. In this paper, Hf was used to partially replace Pt to form Graphene@(PtSe2)n(HfSe2)4−n (n = 1, 2, and 3) bidirectional heterostructures consisting of graphene and lateral PtSe2/HfSe2 composites based on first-principles calculations. Then, the new bidirectional heterostructures were compared with heterostructures formed by graphene with pure MSe2 (M = Pt, Hf). It was found that the band gaps of the bidirectional heterostructures were between those of Graphene@PtSe2 and Graphene@HfSe2. Among these heterostructures, the Graphene@(PtSe2)3(HfSe2)1 bidirectional heterostructure has almost the same optical absorption properties in the infrared wavelength region of 1.33~40 µm as the Graphene@PtSe2 heterostructure, and it improves the absorption in the near-infrared wavelength region of 0.75~1.33 µm. Such a designment may bring the material costs down (since PtSe2 costs approximately five times more than HfSe2). This study on the designment of the bidirectional Graphene@(PtSe2)3(HfSe2)1 heterostructure also illustrates a cost-effective design method for Pt-based IR detectors.

Inspired by some previous surveys, we obtained significant electrochromic properties by hydrothermal synthesis using a solution of Iron (II) Chloride, Ammonium Metatungstate, Sodium Hydroxide and Hydrochloric Acid. The respond time of the electrochromic device was accelerated by iron (II) chloride that the coloring time was 6.5s while the bleaching time was 11.5s at the molar concentration ratio of 1:3.5 between ammonium metatungstate and iron (II) chloride, PH=2.5. Meanwhile the device had a significant optical modulation of 65% with air serving as a blank. Influenced by the acidic environment, the aqueous solution will occur hydrogen evolution reaction (HER) which dramatically deteriorated the stable of active layer over a long period of cycling. Here we innovatively apply a hydrogen bond acceptor, dimethyl sulfoxide (DMSO) to the formulation, the open circuit voltage of HER can be increased as well as the overpotential through restricting all hydrogen atoms of the water molecules in the DMSO‐H2O H‐bond network which can achieve the effect of maintaining a steady cycle of over 800 cycles.