Supercapacitors attract great interest because of the increasing and urgent demand for environment‐friendly high‐power energy sources. Ti3C2, a member of MXene family, is a promising electrode material for supercapacitors owing to its excellent chemical and physical properties. However, the highest gravimetric capacitance of the MXene‐based electrodes is still relatively low (245 F g−1) and the key challenge to improve this is to exploit more pseudocapacitance by increasing the active site concentration. Here, a method to significantly improve the gravimetric capacitance of Ti3C2Tx MXenes by cation intercalation and surface modification is reported. After K+ intercalation and terminal groups (OH−/F−) removing , the intercalation pseudocapacitance is three times higher than the pristine MXene, and MXene sheets exhibit a significant enhancement (about 211% of the origin) in the gravimetric capacitance (517 F g−1 at a discharge rate of 1 A g−1). Moreover, the as‐prepared electrodes show above 99% retention over 10 000 cycles. This improved electrochemical performance is attributed to the large interlayer voids of Ti3C2 and lowest terminated surface group concentration. This study demonstrates a new strategy applicable to other MXenes (Ti2CTx, Nb2CTx, etc.) in maximizing their potential applications in energy storage.

excited charges should separate from each other and migrate to the surface to perform photocatalytic reactions, before they are annihilated in the recombination process. [ 3,17,18 ] Nevertheless, TiO 2 has a wide bandgap of 3.0−3.2 eV for the three common natural polymorphs -anatase, rutile and brookite. [ 8 ] That limits the optical absorption of TiO 2 in the ultraviolet (UV) region of the solar spectrum, resulting in insuffi cient utilization of solar energy (less than 5%). Another hurdle for TiO 2 material in the photo-chemical applications is its low quantum effi ciency that results from its high recombination of photo-generated electron-hole pairs. [ 16,18 ] Therefore, improving the optical absorption properties and reducing electron-hole recombination of TiO 2 are expected to be signifi cant for superior photoactivity.Various strategies have been adopted to tune TiO 2 's optical and electronic properties to improve its visible-light photoactivity. For example, metal ions (Co, Ni, Mn, Fe, Cr, …) or non-metal ions (N, S, C, I, …) are doped in the titania matrix to induce mid-gap states or to narrow the bandgap of TiO 2 , aiming to enhance its visible-light response. [ 3,17 ] Doping with open-shell metals is claimed to be benefi cial for red-shifting TiO 2 photochemistry into the visible, while closed shell cation dopants have no photochemical benefi t. Some d -block transition metal doping often generates deeply localized d -states in the forbidden bandgap of TiO 2 and results in recombination centers for carriers. [ 3,19 ] For the incorporation of non-metal ions, heavy doping is always diffi cult due to the large differences in chemistry between the alien ions and O 2− in titania, thus the visible light absorption is not signifi cantly enhanced. [ 20 ] Dye-sensitized or noble metal nanodots decorated TiO 2 nanostructures have been largely designed to enhanced its optical properties and to improve the charge separation effi ciency. [ 6,9,15,17,21 ] Additionally, charge separation in TiO 2 is believed to be effi ciently improved by forming heterojunctions with other semiconductors, such as metal oxides and chalcogenides. [ 6,22 ] In 2011, a hydrogenated black titania with a narrowed bandgap of ≈1.5 eV was reported to boost the full spectrum sunlight absorption and the photocatalytic activity. [ 23 ] This discovery has triggered world-wide scientifi c interests in black TiO 2 nanomaterials. [ 8 ] Black TiO 2 is featured by selfstructural modifi cations, involving self-doped Ti 3+ /oxygen vacancy, or incorporation of H-doping. [ 5,8 ] Owing to these modifi cations, their crystal and electronic structures as well as the surface property are signifi cantly changed, and the most marked effect is the color changing. The intrinsic TiO 2The photocatalytic activity of TiO 2 has aroused a broad range of research effort since 1972. Although TiO 2 has a very high effi ciency in utilizing ultraviolet light, its overall solar activity is very limited due to its wide bandgap (≈3.0−3.2 eV). This is a bottleneck for TiO 2 to...

TiO mesoporous crystal has been prepared by one-step corroding process via an oriented attachment (OA) mechanism with SrTiO as precursor. High resolution transmission electron microscopy (HRTEM) and nitrogen adsorption-desorption isotherms confirm its mesoporous crystal structure. Well-dispersed ruthenium (Ru) in the mesoporous nanocrystal TiO can be attained by the same process using Ru-doped precursor SrTiRu O. Ru is doped into lattice of TiO, which is identified by HRTEM and super energy dispersive spectrometer (super-EDS) elemental mapping. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectroscopy (EPR) suggest the pentavalent Ru but not tetravalent, while partial Ti in TiO accept an electron from Ru and become Ti, which is observed for the first time. This Ru-doped TiO performs high activity for electrocatalytic hydrogen evolution reaction (HER) in alkaline solution. First-principles calculations simulate the HER process and prove TiO:Ru with Ru and Ti holds high HER activity with appropriate hydrogen-adsorption Gibbs free energies (Δ G).

SnO -based lithium-ion batteries have low cost and high energy density, but their capacity fades rapidly during lithiation/delithiation due to phase aggregation and cracking. These problems can be mitigated by using highly conducting black SnO , which homogenizes the redox reactions and stabilizes fine, fracture-resistant Sn precipitates in the Li O matrix. Such fine Sn precipitates and their ample contact with Li O proliferate the reversible Sn → Li Sn → Sn → SnO /SnO cycle during charging/discharging. SnO electrode has a reversible capacity of 1340 mAh g and retains 590 mAh g after 100 cycles. The addition of highly conductive, well-dispersed reduced graphene oxide further stabilizes and improves its performance, allowing 950 mAh g remaining after 100 cycles at 0.2 A g with 700 mAh g at 2.0 A g . Conductivity-directed microstructure development may offer a new approach to form advanced electrodes.