Engineering electronic structures of titanium vacancies in Ti_(1-x)O_(2)nanosheets enables enhanced Li-ion and Na-ion storage

Up to now,three kinds of ion-storage mechanisms are summarized towards anode materials in lithium/sodium-ion batteries,but they have low capacity and poor cyclic performance.Therefore,it is necessary to develop a new approach to optimize ion storage.Herein,we report an adsorption/desorption storage route through engineering electronic structure of cation-deficient Ti_(1-x)O_(2)nanosheets.Ti_(1-x)O_(2)nanosheets indeed exhibit higher capacity(332.1 mA h g^(-1)vs.137.7 mA h g^(-1)for LIBs,195.7 mA h g^(-1)vs.111 mA h g^(-1)for SIBs),and more stable cyclic performance(296 mA h g^(-1)vs.99 mA h g^(-1)for LIBs,178.1 mA h g^(-1)vs.80.2 mA h g^(-1)for SIBs after 100 cycles)at 0.1 A g^(-1)than TiO_(2)nanosheets.Kinetics analysis and density functional theory(DFT)calculations reveal that electronic structures of vacancy within Ti_(1-x)O_(2) nanosheets encourage a novel adsorption-desorption storage route.These results highlight the benefits of the engineered electronic structures within electrode material and implement novel ion-storage mechanism towards broad energy storage applications.

Fe^(3+)-stabilized Ti_(3)C_(2)T_(x) MXene enables ultrastable Li-ion storage at low temperature

It is highly important to develop ultrastable electrode materials for Li-ion batteries(LIBs),especially in the low temperature.Herein,we report Fe^(3+)-stabilized Ti_(3)C_(2)T_(x) MXene(donated as T/F-4:1)as the anode material,which exhibits an ultrastable low-temperature Li-ion storage property(135.2 m A h g^(-1)after300 cycles under the current density of 200 m A g^(-1)at-10℃),compared with the negligible capacity for the pure Ti_(3)C_(2)T_(x) MXene(26 m A h g^(-1)at 200 m A g^(-1)).We characterized as-made T/F samples via the Xray photoelectron spectroscopy(XPS),Fourier transformed infrared(FT-IR)and Raman spectroscopy,and found that the terminated functional groups(-O and-OH)in T/F are Li^(+) storage sites.Fe^(3+)-stabilization makes-O/-OH groups in MXene interlayers become active towards Li^(+),leading to much more active sites and thus an enhanced capacity and well cyclic stability.In contrast,only-O/-OH groups on the top and bottom surfaces of pure Ti_(3)C_(2)T_(x) MXene can be used to adsorb Li^(+),resulting in a low capacity.Transmission electron microscopy(TEM)and XPS data confirm that T/F-4:1 holds the highly stable solid electrolyte interphase(SEI)layer during the cycling at-10℃.Density functional theory(DFT)calculations further uncover that T/F has fast diffusion of Li^(+) and consequent better electrochemical performances than pure Ti_(3)C_(2)T_(x) MXene.It is believed that the new strategy used here will help to fabricate advanced MXene-based electrode materials in the energy storage application.

Revealing the Role of d Orbitals of Transition-Metal-Doped Titanium Oxide on High-Efficient Oxygen Reduction

Precise catalysis is critical for the high-quality catalysis industry.However,it remains challenging to fundamentally understand precise catalysis at the atomic orbital level.Herein,we propose a new strategy to unravel the role of specific d orbitals in catalysis.The oxygen reduction reaction(ORR)catalyzed by atomically dispersed Pt/Co-doped Ti_(1−x)O_(2) nanosheets(Pt_(1)/Co_(1)-Ti_(1−x)O_(2))is used as a model catalysis.The z-axis d orbitals of Pt/Co-Ti realms dominate the O2 adsorption,thus triggering ORR.In light of orbital-resolved analysis,Pt_(1)/Co_(1)-Ti_(1−x)O_(2) is experimentally fabricated,and the excellent ORR catalytic performance is further demonstrated.Further analysis reveals that the superior ORR performance of Pt_(1)-Ti_(1−x)O_(2) to Co_(1)-Ti_(1−x)O_(2) is ascribed to stronger activation of Ti by Pt than Co via the d-d hybridization.Overall,this work provides a useful tool to understand the underlying catalytic mechanisms at the atomic orbital level and opens new opportunities for precise catalyst design.

Engineering Electronic Structure of Single-Atom Pd Site on Ti_(0.87)O_(2)Nanosheet via Charge Transfer Enables C-Br Cleavage for Room-Temperature Suzuki Coupling

The palladium(Pd)-catalyzed Suzuki reaction is widely applied in the pharmaceutical industry,where constructing highly active and low-cost Pd sites are impendent.Here,we report the fabrication of a heterogeneous Pd/Tio2 catalyst via engineering of an electronic structure of a single Pd_(1)atom on monolayered Ti_(0.87)O_(2)nanosheet(Pd_(1)-Ti_(0.87)O_(2)).This catalyst motivated the kinetically sluggish C-Br cleavage,thus boosting the Suzuki reaction at room temperature.Pd_(1)-Ti_(0.87)O_(2)exhibited an outstanding activity with turnover frequency(TOF)of 11,110 h-1,exceeding that of PdCl_(2)and Pd(OAc)_(2)catalysts by a factor of>200.Various in situ techniques were employed to investigate the C-Br activation process,which showed that Pd_(1)kinetic-feasibly dissociated the chemisorbed bromobenzene,especially the C-Br bond cleavage.Theoretical calculations further revealed that the improved activity is ascribed to the optimized charge state of Pd_(1)within the Pd_(1)O4 realm via charge transfer.