The design of low-cost yet high-efficiency electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) over a wide pH range is highly challenging. We now report a hierarchical co-assembly of interacting MoS 2 and Co 9 S 8 nanosheets attached on Ni 3 S 2 nanorod arrays which are supported on nickel foam (NF). This tiered structure endows high performance toward HER and OER over a very broad pH range. By adjusting the molar ratio of the Co:Mo precursors, we have created CoMoNiS-NF-xy composites (x:y means Co:Mo molar ratios ranging from 5:1 to 1:3) with controllable morphology and composition. The three-dimensional composites have an abundance of active sites capable of universal pH catalytic HER and OER activity. The CoMoNiS-NF-31 demonstrates the best electrocatalytic activity, giving ultralow overpotentials (113, 103, and 117 mV for HER and 166, 228, and 405 mV for OER) to achieve a current density of 10 mA cm −2 in alkaline, acidic, and neutral electrolytes, respectively. It also shows a remarkable balance between electrocatalytic activity and stability. Based on the distinguished catalytic performance of CoMoNiS-NF-31 toward HER and OER, we demonstrate a two-electrode electrolyzer performing water electrolysis over a wide pH range, with low cell voltages of 1.54, 1.45, and 1.80 V at 10 mA cm −2 in alkaline, acidic, and neutral media, respectively. First-principles calculations suggest that the high OER activity arises from electron transfer from Co 9 S 8 to MoS 2 at the interface, which alters the binding energies of adsorbed species and decreases overpotentials. Our results demonstrate that hierarchical metal sulfides can serve as highly efficient all-pH (pH = 0−14) electrocatalysts for overall water splitting.

The MoS4(2-) ion was intercalated into magnesium-aluminum layered double hydroxide (MgAl-NO3-LDH) to produce a single phase material of Mg0.66Al0.34(OH)2(MoS4)0.17·nH2O (MgAl-MoS4-LDH), which demonstrates highly selective binding and extremely efficient removal of heavy metal ions such as Cu(2+), Pb(2+), Ag(+), and Hg(2+). The MoS4-LDH displays a selectivity order of Co(2+), Ni(2+), Zn(2+) < Cd(2+) ≪ Pb(2+) < Cu(2+) < Hg(2+) < Ag(+) for the metal ions. The enormous capacities for Hg(2+) (∼500 mg/g) and Ag(+) (450 mg/g) and very high distribution coefficients (Kd) of ∼10(7) mL/g place the MoS4-LDH at the top of materials known for such removal. Sorption isotherm for Ag(+) agrees with the Langmuir model suggesting a monolayer adsorption. It can rapidly lower the concentrations of Cu(2+), Pb(2+), Hg(2+), and Ag(+) from ppm levels to trace levels of ≤1 ppb. For the highly toxic Hg(2+) (at ∼30 ppm concentration), the adsorption is exceptionally rapid and highly selective, showing a 97.3% removal within 5 min, 99.7% removal within 30 min, and ∼100% removal within 1 h. The sorption kinetics for Cu(2+), Ag(+), Pb(2+), and Hg(2+) follows a pseudo-second-order model suggesting a chemisorption with the adsorption mechanism via M-S bonding. X-ray diffraction patterns of the samples after adsorption demonstrate the coordination and intercalation structures depending on the metal ions and their concentration. After the capture of heavy metals, the crystallites of the MoS4-LDH material retain the original hexagonal prismatic shape and are stable at pH ≈ 2-10. The MoS4-LDH material is thus promising for the remediation of heavy metal polluted water.

There is a need to develop highly selective and efficient materials for capturing uranium (normally as UO2(2+)) from nuclear waste and from seawater. We demonstrate the promising adsorption performance of S(x)-LDH composites (LDH is Mg/Al layered double hydroxide, [S(x)](2-) is polysulfide with x = 2, 4) for uranyl ions from a variety of aqueous solutions including seawater. We report high removal capacities (q(m) = 330 mg/g), large K(d)(U) values (10(4)-10(6) mL/g at 1-300 ppm U concentration), and high % removals (>95% at 1-100 ppm, or ∼80% for ppb level seawater) for UO2(2+) species. The S(x)-LDHs are exceptionally efficient for selectively and rapidly capturing UO2(2+) both at high (ppm) and trace (ppb) quantities from the U-containing water including seawater. The maximum adsorption coeffcient value K(d)(U) of 3.4 × 10(6) mL/g (using a V/m ratio of 1000 mL/g) observed is among the highest reported for U adsorbents. In the presence of very high concentrations of competitive ions such as Ca(2+)/Na(+), S(x)-LDH exhibits superior selectivity for UO2(2+), over previously reported sorbents. Under low U concentrations, (S4)(2-) coordinates to UO2(2+) forming anionic complexes retaining in the LDH gallery. At high U concentrations, (S4)(2-) binds to UO2(2+) to generate neutral UO2S4 salts outside the gallery, with NO3(-) entering the interlayer to form NO3-LDH. In the presence of high Cl(-) concentration, Cl(-) preferentially replaces [S4](2-) and intercalates into LDH. Detailed comparison of U removal efficiency of S(x)-LDH with various known sorbents is reported. The excellent uranium adsorption ability along with the environmentally safe, low-cost constituents points to the high potential of S(x)-LDH materials for selective uranium capture.

Sulfur cathodes in conversion reaction batteries offer high gravimetric capacity but suffer from parasitic polysulfide shuttling. We demonstrate here that transition metal chalcogels of approximate formula MoS 3.4 achieve high gravimetric capacity close to 600 mAh g −1 (close to 1000 mAh g −1 on a sulfur-basis), as electrode materials for lithium-ion batteries. Transition metal chalcogels are amorphous, and comprise polysulfide chains connected by inorganic linkers. The linkers appear to act as a "glue" in the electrode to prevent polysulfide shuttling. The Mo chalcogels function as electrodes in carbonate-as well as ether-based electrolytes, which further provides evidence for polysulfide solubility not being a limiting issue. We employ X-ray spectroscopy and operando pair distribution function techniques to elucidate the structural evolution of the electrode. Raman and X-ray photoelectron spectroscopy track the chemical moieties that arise during the anion-redox-driven processes. We find the redox state of Mo remains unchanged across the electrochemical cycling and correspondingly, the redox