2D MoO 3 Nanosheets Synthesized by Exfoliation and Oxidation of MoS 2 for High Contrast and Fast Response Time Electrochromic Devices

MoO 3 has potential advantages in price and weight over more widely studied WO 3 for electrochromic devices, but it typically suffers from inferior electrochromic performance. Here, it is demonstrated that 2D MoO 3 nanosheets can be formed by intercalation and exfoliation of MoS 2 to form partially oxidized MoS x O y, followed by complete oxidation using a solution-phase nitric acid treatment. These fully oxidized MoO 3 nanosheets retain the 2D nature of exfoliated MoS 2 (70% of nanosheets are less than 9 nm thick), allowing for easier ionic diffusion through the film compared to bulk MoO 3 powder. When utilized as an electrochromic material, the device showed outstanding contrast (48.6% at 700 nm) and fast response time (11.3 s for bleaching, 9.8 s for coloration), which is far superior to that for standard powder MoO 3 and comparable to that for many nanostructures of WO 3 . This shows the outstanding potential for these MoO 3 nanosheets in electrochromic applications.