Achieving ultrahigh electrochemical performance by surface design and nanoconfined water manipulation

Abstract

The effects of nanoconfined water and charge storage mechanism are crucial in achieving ultrahigh electrochemical performance of two-dimensional (2D) transition metal carbides (MXenes). We propose a facile method to manipulate the nanoconfined water through surface chemistry modification. By introducing oxygen and nitrogen surface groups, more active sites were created for Ti3C2 MXene, also with the interlayer spacing significantly increased by accommodating three-layer nanoconfined water. Exceptionally high capacitance of 550 F g–1 (2000 F cm–3) was obtained with outstanding high-rate performance. The atomic scale elucidation of layer-dependent properties of nanoconfined water and pseudocapacitive charge storage was deeply probed through a combination of ‘computational and experimental microscopy’. We believe the understanding and manipulation strategy of nanoconfined water will shed light on pushing MXene and other 2D materials to better electrochemical performance.

A General Strategy to Synthesize Fluidic Single Atom Electrodes for Selective Reactive Oxygen Species Production

“…The crystalline phase of the CrN 4 /MXene and CrO 4 /MXene electrodes was studied with X-ray diffraction (XRD), which exhibited no evident changes after N-doping, in good agreement with a pure MXene electrode (Figure d). , However, the lattice constant of CrN 4 /MXene ( a = 3.9532) was slightly larger than that of CrO 4 /MXene ( a = 3.1061), suggesting that the N-doping led to distortion of the lattice. Likewise, Raman spectra of the CrN 4 /MXene electrode had a blue shift compared with the CrO 4 /MXene electrode, possibly due to an increase in the grain size during the N-doping (Figure e).…”

“…29,30 The crystalline phase of the CrN 4 /MXene and CrO 4 / MXene electrodes was studied with X-ray diffraction (XRD), which exhibited no evident changes after N-doping, in good agreement with a pure MXene electrode (Figure 2d). 31,32 However, the lattice constant of CrN 4 /MXene (a = 3.9532) due to an increase in the grain size during the N-doping (Figure 2e). In addition, the Fourier transform infrared (FTIR) spectrum of CrN 4 /MXene (Figure 2f) exhibited a decrease in the −OH intensity at 3400 cm −1 and an increase in bonds, 34,35 underscoring the successful incorporation of N elements into the MXene matrix and their coordination with Cr atoms.…”

Unifying electrolyte formulation and electrode nanoconfinement design to enable new ion–solvent cointercalation chemistries

“…The hydrophilic, N-O-terminated interlayer chemistry caused a partial interlayer hydration after soaking of the electrode in electrolyte for several hours, and an increasing number of water molecules entering the interlayer space during proton intercalation. 51,52 Similar effects of nanoconfinement chemistry design were also demonstrated for lithium intercalation from organic electrolyte by Ba ¨rmann et al, who utilized acidic or basic post-synthesis treatment of Ti 3 C 2 T x MXenes. 53 The authors found large structural changes during lithium intercalation via in situ XRD only for base-treated MXene, which was ascribed to cointercalation of carbonate solvents, which was not observed for acid-treated MXenes.…”

Enhancing ion storage and transport in Ti3C2Tz MXene via a “sacrificial cations” strategy

“…The electrodes prepared by the “sacrificial cation” method have strong hydrophilicity with aqueous electrolyte, which is favorable for energy storage. 43 However, it is well known that alkylammonium cations easily decompose into NH 3 and acid during calcination (will be discussed in Fig. 3(f)).…”