Electrochemically converting nitrate, a widespread water pollutant, back to valuable ammonia is a green and delocalized route for ammonia synthesis, and can be an appealing and supplementary alternative to the Haber-Bosch process. However, as there are other nitrate reduction pathways present, selectively guiding the reaction pathway towards ammonia is currently challenged by the lack of efficient catalysts. Here we report a selective and active nitrate reduction to ammonia on Fe single atom catalyst, with a maximal ammonia Faradaic efficiency of ~ 75% and a yield rate of up to ~ 20,000 μg h−1 mgcat.−1 (0.46 mmol h−1 cm−2). Our Fe single atom catalyst can effectively prevent the N-N coupling step required for N2 due to the lack of neighboring metal sites, promoting ammonia product selectivity. Density functional theory calculations reveal the reaction mechanisms and the potential limiting steps for nitrate reduction on atomically dispersed Fe sites.

Two-dimensional transition-metal carbide materials (termed MXene) have attracted huge attention in the field of electrochemical energy storage due to their excellent electrical conductivity, high volumetric capacity, etc. Herein, with inspiration from the interesting structure of pillared interlayered clays, we attempt to fabricate pillared TiC MXene (CTAB-Sn(IV)@TiC) via a facile liquid-phase cetyltrimethylammonium bromide (CTAB) prepillaring and Sn pillaring method. The interlayer spacing of TiC MXene can be controlled according to the size of the intercalated prepillaring agent (cationic surfactant) and can reach 2.708 nm with 177% increase compared with the original spacing of 0.977 nm, which is currently the maximum value according to our knowledge. Because of the pillar effect, the assembled LIC exhibits a superior energy density of 239.50 Wh kg based on the weight of CTAB-Sn(IV)@TiC even under higher power density of 10.8 kW kg. When CTAB-Sn(IV)@TiC anode couples with commercial AC cathode, LIC reveals higher energy density and power density compared with conventional MXene materials.

Hydrogen peroxide (H2O2) synthesis generally requires substantial postreaction purification. Here, we report a direct electrosynthesis strategy that delivers separate hydrogen (H2) and oxygen (O2) streams to an anode and cathode separated by a porous solid electrolyte, wherein the electrochemically generated H+ and HO2– recombine to form pure aqueous H2O2 solutions. By optimizing a functionalized carbon black catalyst for two-electron oxygen reduction, we achieved >90% selectivity for pure H2O2 at current densities up to 200 milliamperes per square centimeter, which represents an H2O2 productivity of 3.4 millimoles per square centimeter per hour (3660 moles per kilogram of catalyst per hour). A wide range of concentrations of pure H2O2 solutions up to 20 weight % could be obtained by tuning the water flow rate through the solid electrolyte, and the catalyst retained activity and selectivity for 100 hours.

Lithium-sulfur batteries show fascinating potential for advanced energy storage systems due to their high specific capacity, low-cost, and environmental benignity. However, the shuttle effect and the uncontrollable deposition of lithium sulfide species result in poor cycling performance and low Coulombic efficiency. Despite the recent success in trapping soluble polysulfides via porous matrix and chemical binding, the important mechanism of such controllable deposition of sulfur species has not been well understood. Herein, we discovered that conductive Magnéli phase Ti4O7 is highly effective matrix to bind with sulfur species. Compared with the TiO2-S, the Ti4O7-S cathodes exhibit higher reversible capacity and improved cycling performance. It delivers high specific capacities at various C-rates (1342, 1044, and 623 mAh g(-1) at 0.02, 0.1, and 0.5 C, respectively) and remarkable capacity retention of 99% (100 cycles at 0.1 C). The superior properties of Ti4O7-S are attributed to the strong adsorption of sulfur species on the low-coordinated Ti sites of Ti4O7 as revealed by density functional theory calculations and confirmed through experimental characterizations. Our study demonstrates the importance of surface coordination environment for strongly influencing the S-species binding. These findings can be also applicable to numerous other metal oxide materials.

Two-dimensional transition metal carbide materials called MXenes show potential application for energy storage due to their remarkable electrical conductivity and low Li(+) diffusion barrier. However, the lower capacity of MXene anodes limits their further application in lithium-ion batteries. Herein, with inspiration from the unique metal ion uptake behavior of highly conductive Ti3C2 MXene, we overcome this impediment by fabricating Sn(4+) ion decorated Ti3C2 nanocomposites (PVP-Sn(IV)@Ti3C2) via a facile polyvinylpyrrolidone (PVP)-assisted liquid-phase immersion process. An amorphous Sn(IV) nanocomplex, about 6-7 nm in lateral size, has been homogeneously anchored on the surface of alk-Ti3C2 matrix by ion-exchange and electrostatic interactions. In addition, XRD and TEM results demonstrate the successful insertion of Sn(4+) into the interlamination of an alkalization-intercalated Ti3C2 (alk-Ti3C2) matrix. Due to the possible "pillar effect" of Sn between layers of alk-Ti3C2 and the synergistic effect between the alk-Ti3C2 matrix and Sn, the nanocomposites exhibit a superior reversible volumetric capacity of 1375 mAh cm(-3) (635 mAh g(-1)) at 216.5 mA cm(-3) (100 mA g(-1)), which is significantly higher than that of a graphite electrode (550 mAh cm(-3)), and show excellent cycling stability after 50 cycles. Even at a high current density of 6495 mA cm(-3) (3 A g(-1)), these nanocomposites retain a stable specific capacity of 504.5 mAh cm(-3) (233 mAh g(-1)). These results demonstrate that PVP-Sn(IV)@Ti3C2 nanocomposites offer fascinating potential for high-performance lithium-ion batteries.