Scalable, inexpensive, one-pot, facile synthesis of crystalline two-dimensional birnessite flakes

MXene//MnO2 Asymmetric Supercapacitors with High Voltages and High Energy Densities

“…When these films are heated in vacuum at 50 °C for 12 h, the XRD patterns (Figure S1) indicate that the d-spacing shrinks to 9.7 Å due to, presumably, the loss of water. If one assumes the thickness of a birnessite layer to be � 2 Å, [20] this implies the TMA + cations are 7.7 Å in diameter, which agrees with our previous work. [21] The Raman spectrum in Figure 1c shows the MnÀ O stretching modes of birnessite, in which the 642.1 cm À 1 and 565.1 cm À 1 peaks correspond to the out-of-plane and in plane basal vibrations, respectively.…”

“…A typical XRD pattern of a TMA + -MnO 2 film (Figure 1b) is characterized by peaks at 7.2°, 14.2°, 21.2°and 28.4°, that are assigned to (001), (002), ( 003) and (004) planes of MnO 2 birnessite. [20] The (001) peak at 7.2°corresponds to d of 24.6 Å. The presence of 4 distinct (00 l) peaks is consistent with our previous work, [20] and is a strong indicator that the sheets are quite well stacked normal to the sheets.…”

“…[20] The (001) peak at 7.2°corresponds to d of 24.6 Å. The presence of 4 distinct (00 l) peaks is consistent with our previous work, [20] and is a strong indicator that the sheets are quite well stacked normal to the sheets. When these films are heated in vacuum at 50 °C for 12 h, the XRD patterns (Figure S1) indicate that the d-spacing shrinks to 9.7 Å due to, presumably, the loss of water.…”

“…In other words, most of the Mn cations are in their + 4 state as previously concluded. [20] The Mo 1. 33 CT z and TMA + -MnO 2 suspensions are dark grayish and brownish in color, respectively, and both show the Tyndall effect, confirming their colloidal states (Figure S6).…”

“…[15,19] Very recently we reported on a bottom-up approach to convert Mn 3 O 4 powders into crystalline Mn-based 2D birnessite nanosheets that can be readily filtered into free-standing films with excellent flexibility. [20] Specifically, we converted 5 different non-water soluble Mn-based precursors (Mn 3 O 4 , Mn 2 O 3 , MnB, Mn 2 AlB 2 and Mn 5 SiB 2 ) into 2D birnessite crystalline flakes via simply heating the precursor powders in 25 wt.% tetramethylammonium hydroxide (TMAH) aqueous solutions at 50 °C to 80 °C for 2 days, respectively. This technique is inexpensive and eminently scalable, with high yields.…”