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.

Iron and nitrogen co‐doped carbon (Fe–N/C) nanomaterials are promising non‐Pt catalysts toward the oxygen reduction reaction (ORR). Both spectroscopy and density functional theory studies reveal that Fe–Nx accounts for the ORR activity. However, Fe–N/C catalysts prepared by traditional high‐temperature pyrolysis always contain less active Fe or Fe3C nanoparticles, and it remains a great challenge to obtain Fe–N/C catalysts with high‐content Fe–Nx active sites. Herein, a 3D space‐confined strategy for the pyrolysis of double‐network aerogels is reported, to obtain Fe–N/C network catalysts with exclusive Fe–Nx active sites without the generation of Fe or Fe3C nanoparticles. The as‐prepared Fe–N/C network exhibits more positive half‐wave potential, higher diffusion‐limited current density, and better selectivity for the ORR than catalysts derived from single aerogels and commercial Pt/C. Additionally, the ORR activity measured in potassium thiocyanate (KSCN) poisoned electrolyte corroborates that Fe–Nx is the active site. This work opens a new guideline for designing the M–N/C catalysts with exclusive active sites in porous carbon matrices for boosting energy electrocatalysis.

displays high acid stability and excellent uptake for heavy metal ions such as Hg 2+ , Ag + , Cu 2+ , and Pb 2+ . The different maximum adsorption capacities (q m ) for Cu 2+ , Pb 2+ , Hg 2+ , and Ag + depend on the various binding modes arising from the different thiophilicity of these metal ions. The removals of Ag + and Pb 2+ reach >99.6% within 5 min, and for highly toxic Hg 2+ , >98% removal achieves at 1 min. At strong acid limit, the exceptional q m (Ag + ) of 725 mg g −1 places the MoS 4 -Ppy at the top of materials for such removal. Uptake kinetics of Ag + , Hg 2+ , and Pb 2+ is extremely fast: >99.9% removal rates at wide pH range (0.5-6) within 1-5 min. Also, at strongly acidic conditions (pH ≈ 1), for highly toxic Hg 2+ , <2 ppb concentration can be achieved, accepted as safe limit. The MoS 4 -Ppy demonstrates an outstanding ability to separate low-concentrated Ag + from high concentrated Cu 2+ especially under strong acidic conditions (pH ≈ 1), showing a large separation factor SF Ag/Cu (K d Ag /K d Cu ) of 10 5 (>100). MoS 4 -Ppy is a superior and novel sorbent material for water remediation applications as well as precious metals recovery.

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Hydrogen energy derived from water splitting is the cleanest renewable energy source, but it is also very challenging to achieve because the hydrogen evolution reaction (HER) requires highly efficient and low-cost electrocatalysts. We have fabricated a novel hierarchical system of amorphous molybdenum oxy/sulfide microspheres with crystalline Ni3S2 intergrown in situ on Ni foam (MoO x S y /Ni3S2/NF) as an outstanding electrocatalyst for HER. The MoO x S y /Ni3S2/NF demonstrates an ultra-low overpotential of 58 mV at a current density of 10 mA cm–2 and extremely durable stability (>200 h), suggesting superior performance comparable to that of Pt-C/NF under acidic conditions. The X-ray absorption fine structure (XAFS) determines the average valence state of Mo to be +(5 + δ), with a coordination motif by O and S. To explain such high HER activity, a [Mo2O2(S,O)4] dimer-based periodic model structure with the average composition of [Mo4O8S4] interfaced with the Ni3S2(101) surface is proposed. The interactions between the Ni of Ni3S2 and bridging S/O of [Mo4O8S4] result in an average formal Mo charge state between +5 and +6, and significant charge transfer from Ni3S2 to [Mo4O8S4] activates the MoO bonds. The calculated |ΔG H*| of less than 50 meV suggests that the double-bonded O is the most active site. This work points to the importance of oxy/sulfides with Mo n+ (+5 < n<+6) as exceptional electrochemical catalysts for HER.

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