The electrochemical reduction of sulfur has been studied employing in situ spectroelectrochemical techniques. Previously unreported absorption bands in the UV region observed during the electrochemical reduction are assigned to the reduced sulfur species with high electron-to-atom ratios. The spectroelectrochemical studies indicate that reduction products generated at the first reduction step are essentially identical to those formed at the second with S~-and S~-as ultimate reduction products. This suggests that chemical reactions following the first electron transfer to produce S~-are important. The derivative cyclic voltabsorptometric (DCVA) results indicate that all the reduced sulfur species, i.e., S~-, S~-, S~-, S~-, and S~" are generated at the first cathodic wave and three of these, i.e., S~-, S~-and S~" are reduced at the second reduction wave, while other species show a delayed generation. A mechanism consistent with these observations is proposed.
Two-dimensional (2D) transitional metal oxides (TMOs) are an attractive class of materials due to the combined advantages of high active surface area, enhanced electrochemical properties, and stability. Among the 2D TMOs, 2D tungsten oxide (WO) nanosheets possess great potential in electrochemical applications, particularly in electrochromic (EC) devices. However, feasible production of 2D WO nanosheets is challenging due to the innate 3D crystallographic structure of WO. Here we report a novel solution-phase synthesis of 2D WO nanosheets through simple oxidation from 2D tungsten disulfide (WS) nanosheets exfoliated from bulk WS powder. The complete conversion from WS into WO was confirmed through crystallographic and elemental analyses, followed by validation of the 2D WO nanosheets applied in the EC device. The EC device showed color modulation of 62.57% at 700 nm wavelength, which is 3.43 times higher than the value of the conventional device using bulk WO powder, while also showing enhancement of ∼46.62% and ∼62.71% in switching response-time (coloration and bleaching). The mechanism of enhancement was rationalized through comparative analysis based on the thickness of the WO components. In the future, 2D WO nanosheets could also be used for other promising applications such as sensors, catalysis, thermoelectric, and energy conversion.
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