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[Display omitted] • Hollow tubular ZnIn 2 S 4 modified with embedded metal-organic-framework-layers (ZnIn 2 S 4 -MOFL) were rationally designed. • Efficient ZnIn 2 S 4 -MOFL released H 2 bubble at the optimum rate of 28.2 mmol/g/h. • The Z-scheme photocatalytic system strongly promoted the separation of electron and hole pairs. • DFT results revealed the decreased density of states of ZnIn 2 S 4 after coupling with the organic ligands of MOFL. This work reported a facile one-step method for constructing hollow tubular ZnIn 2 S 4 modified by metal-organic-framework-layers (MOFL) with In-MOF as precursor to be efficient photocatalysts (ZnIn 2 S 4 -MOFL) for robust photocatalytic hydrogen evolution (PHE). The dominant catalyst of ZnIn 2 S 4 and cocatalytic role of MOFL synergistically promoted the separation of electron and hole pairs due to the direct Z-scheme photocatalytic system, leading to an extraordinarily high PHE activity. The density functional theory (DFT) results revealed the remarkably decreased density of states (DOS) of ZnIn 2 S 4 after coupling with the organic ligands of MOFL, indeed proving an effectively suppressed recombination of charge carriers and benefited the performance of photocatalytic reactions. Experimental PHE results showed that a large number of hydrogen bubbles were visible to naked eyes and the optimal hydrogen evolution reached 28.2 mmol/g/h, the highest value reported so far among ZnIn 2 S 4 -based photocatalysts, and almost 14.8 times higher than that of pristine ZnIn 2 S 4. More importantly, the superior apparent quantum efficiencies (AQEs) of 22.67 % at monochromatic light (350 nm) and the stable hydrogen generation capability (5.7 mmol/g/h) under real sunlight irradiation all confirmed a promising catalyst of ZnIn 2 S 4 -MOFL for hydrogen evolution applications. [ABSTRACT FROM AUTHOR]

• Nitrogen atoms in Ni@NCNT facilitate the in-situ conversion of metallic Ni to Ni3+ species. • Nitrogen atoms in Ni@NCNT weaken the interaction between Ni3+ and CO 2 in urea oxidation. • 1.56 V is required to achieve 10 mA cm−2 in overall urea oxidation for Ni@NCNT. Urea electro-oxidation is an attractive and alternative anodic reaction in the electrochemical generation of hydrogen using wastewater ascribing to the low theoretical voltage and non-precious metal (nickel) catalyst for urea oxidation reaction (UOR); however, the sluggish UOR and poisoning of catalyst impede the practical application. Here, in this work, we synthesize a series of nickel nanoparticles embedded nitrogen doped carbon nanotubes (Ni@NCNT) and study the effect of nitrogen dopants on UOR catalytic activity. The nitrogen dopants can weaken the binding strength between CO 2 species and active sites resulting in alleviation of CO 2 poisoning; simultaneously, nitrogen dopants also promote the in-situ conversion of Ni3+ species facilitating UOR catalysis; as a result, electrocatalytic current density of 45.8 mA cm−2 is recorded for Ni@NCNT in 1 M KOH electrolyte with 0.5 M urea at 1.5 V vs. RHE, which is 3.8 fold better than commercial Pt/C (11.8 mA cm−2). Moreover, Ni@NCNT, due to the more nitrogen dopants, exhibits a comparable overpotential to commercial Pt/C for driving hydrogen evolution reaction (HER) catalysis in 1 M KOH electrolyte at high current density (400 mA cm−2). Subsequently, 1.56 V is demanded for overall UOR catalysis on Ni@NCNT with current density of 10 mA cm−2. This work offers useful information for designing a stable and efficient electrocatalyst for not only UOR but also electrochemical generation of H 2 from wastewater. [ABSTRACT FROM AUTHOR]

• CoWO 4-x @C exhibits comparable HER activity to Pt/C in acidic and alkaline mediums. • CoWO 4-x @C requires only 295 mV overpotential to deliver 10 mA cm−2 in the OER test. • 1.57 V is required for CoWO 4-x @C to attain 10 mA cm−2 in alkaline water splitting. Development of earth-abundant, efficient and stable electrocatalysts for water splitting is of crucial importance for environmentally friendly energy conversion and storage. Here, we report an oxygen deficient cobalt tungstate nanoparticles with diameter of 8 nm (CoWO 4-x @C) as efficient bifunctional electrocatalyst for hydrogen evolution reaction (HER) and oxygen reduction reaction (OER), which exhibits comparable HER activity to commercial Pt/C with overpotentials of 32.5 mV and 46.8 mV vs. RHE to deliver current density of 10 mA cm−2 in acidic and alkaline mediums, respectively, ascribed to the rich oxygen vacancies facilitating the hydrogen adsorption and its relative recombination, respectively. Additionally, undetectable degradation is observed for CoWO 4-x @C after 10,000 potential cycles indicating high durability. Meanwhile, CoWO 4-x @C requires only 295 mV overpotential to deliver 10 mA cm−2 in the OER test, which is better than the benchmarking IrO 2 (313 mV). 1.57 V comparably lower than Pt/C-IrO 2 (1.59 V) is required for achieving the water splitting current density of 10 mA cm−2 without any degradation for 12 h. [ABSTRACT FROM AUTHOR]