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Urea electrolysis is an appealing energy conversion technology to produce hydrogen (H2) and alleviate the problem of urea-rich wastewater treatment concurrently. In particular, electrocatalytic performance can be dramatically enhanced by rationally modulating the surface charge distribution with a well-tuned heterostructure. Herein, a heterostructure is constructed by NiMoO4 nanosheets grown on an interior hollow NiS@Ni3S2 nanorods framework (NiS@Ni3S2/NiMoO4). Density functional theory (DFT) calculations demonstrate that the formed heterojunction structure leads to a tailored surface charge state of NiMoO4, with oxygen as the nucleophilic region and molybdenum as the electrophilic region, which facilitates the decomposition of urea molecules and thus significantly improves hydrogen evolution. As expected, the assembled NiS@Ni3S2/NiMoO4 system substantially expedites urea electrolysis activity with a cell voltage of 1.40 V at 10 mA cm−2, which is 200 mV less than the voltage of an overall water splitting system.

A 3D NiCo2S4 nanowire arrays directly grown on Ni foam electrode (NiCo2S4/NF) is prepared by two-step simple hydrothermal process. The morphology and phase composition of NiCo2S4/NF are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). As expected, in the following electrocatalytic measurement, the binder-free, self-made NiCo2S4/NF electrode exhibits much higher catalytic activity, lower onset potential, better stability and greater tolerance towards urea electrooxidation compared with the Ni3S2/NF electrode synthesized under the same reaction conditions. The NiCo2S4/NF electrode delivers a current density of 720 mA cm−2 at 0.18 V (vs. Ag/AgCl) in a solution containing 5 mol L−1 KOH and 0.33 mol L−1 urea. The impressive electrocatalytic activity of the NiCo2S4/NF catalyst is largely ascribed to its distinctive structure, which exposes more electrochemical active sites at the electrode–electrolyte interface. Besides, the high intrinsic electronic conductivity also largely boosts the charge transfer rates for urea electrooxidation. The results demonstrate that the NiCo2S4/NF electrode showing a beneficial application prospect in the wastewater treatment and direct urea fuel cells.

NiCo2O4 nanowire arrays grown on Ni foam (NiCo2O4/NF) are synthesized by a simple template-free hydrothermal route followed by a thermal treatment in the air at 400 °C. The as-prepared Ni foam substrate exhibits homogeneous and porous nanowire arrays, which providing a number of active sites and electronic transmission channels for urea electrooxidation. The electroactivity of NiCo2O4/NF electrode toward the oxidation of urea in alkaline solution is evaluated using cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) measurements. Results show that the as-obtained electrode delivers an outstanding electrocatalytic activity and stability for urea electrooxidation. The NiCo2O4/NF electrode delivers a low open potential at 0.19 V versus Ag/AgCl with a corresponding current density of 570 mA cm−2 in 5 mol L−1 KOH and 0.33 mol L−1 urea electrolytes. Meanwhile, detailed investigation is made for the electrocatalytic oxidation of urea by varying several reaction parameters, such as scan rate, urea and KOH concentrations. Benefiting from the unique structure and synergistic effects of Ni and Co, the NiCo2O4/NF electrode exhibit superior electrocatalyst activity and is considered to be a promising candidate catalysis material for direct urea fuel cell.

Urea electrolysis offers the prospect of cost-effective and energy-saving hydrogen production together with mitigating urea-rich wastewater pollution instead of overall water splitting. Hence, here, high-efficiency bifunctional electrocatalysts were developed for both the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) via the in situ vertical growth of thorny leaf-like (2D nanosheets supporting 1D nanowires) NiCoP on a carbon cloth (NiCoP/CC). After integrating the advantages of the synergistic effect between Ni and Co as well as the unique hierarchical structure combined with 1D nanowires, 2D nanosheets and a 3D conductive carbon cloth substrate, the electrode exhibited excellent electrocatalytic activity toward HER and UOR. The electrolytic cell assembled using NiCoP/CC as the anode and the cathode could provide current density of 10 mA cm−2 at a cell voltage of 1.42 V (160 mV less than that for its urea-free counterpart) as well as remarkable durability over 30 h. Thus, the cost-effectiveness and high activity of the NiCoP/CC electrode pave the way to explore transition metal-based electrocatalysts for urea electrolysis.

Ti 3+ doping in TiO 2 photocatalyst has attracted much attention due to its enhanced visible-light absorption and the decreased carrier recombination. However, the introduction of massive stable Ti 3+ is still a great challenge because Ti 3+ is easy to be oxidized in air. In this work, for the first time, a negatively charged core/shell TiO 2 /C nanostructure is prepared and then Pt 0 atoms reduced by NaBH 4 are loaded on its surface. Through a tracking test of the product’s Zeta potential, XPS and FTIR measurements, it is found that the reductive electrons are produced due to the reaction between C and metal Pt, in which Pt exhibits a +2 chemical valence. And the lost electrons by Pt are transferred into the interior TiO 2 through the carbon shell and reduce Ti 4+ to Ti 3+ . This method avoids Ti 3+ ions’ exposing to air and overcomes the complex coating process for isolating oxygen, and provides a new facile one for efficiently Ti 3+ self-doping. Through the following measurements, such as XPS, PL, EPR and Raman etc., it is proved that massive Ti 3+ ions are formed in the interior TiO 2 , which greatly narrows the composite’s band-gap (from 3.11 eV to 2.47 eV) and enhances the visible-light absorption. As a result, the as-obtained sample exhibits a larger carrier densities (13.9 × 10 18 cm −3 ) and a higher photocatalytic activity under visible-light irradiation compared with those in other literatures: the rate of photocatalytic water splitting for H 2 generation is up to 8117 μmol h −1 g −1 .

In this work, a microwave welding method has been used for the construction of chemical Ni-C bonding at the interface between carbon nanotubes (CNTs) and metal Ni to provide a different surface electron distribution, which determined the electromagnetic (EM) wave absorption properties based on a surface plasmon resonance mechanism. Through a serial of detailed examinations, such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectrum, the as-expected chemical Ni-C bonding between CNTs and metal Ni has been confirmed. And the Brunauer-Emmett-Teller and surface zeta potential measurements uncovered the great evolution of structure and electronic density compared with CNTs, metal Ni, and Ni-CNT composite without Ni-C bonding. Correspondingly, except the EM absorption due to CNTs and metal Ni in the composite, another wide and strong EM absorption band ranging from 10 to 18 GHz was found, which was induced by the Ni-C bonded interface. With a thinner thickness and more exposed Ni-C interfaces, the Ni-CNT composite displayed less reflection loss.

The construction of semiconductor composites is known a powerful method to realize the spatial separation of electrons and holes, which results in more electrons or holes dispersing on the surface, accompanying a charge transfer and further extending the region of charge depletion at the interface between these two components of the composite. However, most of them are based on a random accumulation connection of two different crystals and there are obvious empty spaces, which are formed as deplete layer to hinders the charge transfer to a large extent. In order to shorten the charger transfer path and make a direct charge transform from interface to surface, a chemically bonded interface in the composite is more reasonable. In this work, using one-dimensional TiO 2 -C composite nanorods with a Ti–C chemically bonded interface as a touchstone, which was prepared through a simple carbonized process, the above strategy for better semiconductor photocatalytic water splitting property has been realized.

The production and storage of hydrogen are the two most critical challenges for hydrogen energy development. In addition, converting H2 from the as-obtained gas state to a stable storage state consumes excess energy and increases the practical cost of hydrogen fuel. Accordingly, we now present a simple hybrid material system (Co/TiO2) that efficiently synchronizes hydrogen photogeneration in water with its room-temperature storage. In the composite, through a series of carefully controlled experiments, ultrathin Co shells composed of 1, 2, 4, and 9 atom layers have been fabricated on TiO2 photocatalysts. Before saturation of hydrogen on metal Co, the hydrogen storage efficiency is close to 100%, meaning that nearly all hydrogen generated by photocatalytic water splitting is conserved. This work provides a new approach to combined structure-function design technology in the hydrogen energy field.

Urea oxidation reaction (UOR) is considered as a prospective technology for hydrogen generation and degradation of urea-rich wastewater concurrently. In theory, nickel-based catalysts exhibit superior activity in this regard. However, the intrinsically low conductivity and limited active sites on usual nickel-based catalysts impede their applications in UOR. Hence, a hierarchical triple-layered heterostructure, which consists of MnCo2O4.5 nanosheets seamlessly sandwiched between a bottom layer of Ni foam substrate and a top layer of Ni(OH)2 nanosheets, are directly synthesized via a successive hydrothermal-calcination-hydrothermal process (MnCo2O4.5@Ni(OH)2/NF). Taking advantages of the distinctive sandwich structure and the synergistic effect between MnCo2O4.5 and Ni(OH)2, the resulting MnCo2O4.5@Ni(OH)2/NF electrode presents superior electrocatalytic activity with a small onset potential of 0.19 V versus Ag/AgCl as well as a current density of 650 mA cm−2 in 5 M KOH and 0.33 M urea electrolyte. This work provides a promising platform for designing an effective hybrid material toward a wide range of electrochemical applications.

Hybridization of inorganic compounds with graphene-based materials can give rise to various enhanced properties, in which constructing a chemical bond stabilized hybrid structure is of primary importance. In this work, an archetypical hybrid material has been prepared by the reaction of an inorganic CoB noncrystal with graphene at room temperature with a high-energy ball-milling process. Experimental characterization results prove that the inorganic CoB noncrystal is stably pinned to graphene through B–C chemical bonds. The hybrid material shows a high electrochemical hydrogen storage capacity at room temperature. Based on the detailed experimental measurements and theory calculations, the enhanced electrochemical hydrogen storage ability is identified as a Kubas-enhanced hydrogen adsorption mechanism induced by the Co–B–C structure.

Lithium-selenium batteries, employing selenium as a cathode material, exhibit some notable advantages, such as high discharge rates and good cycling performance, due to their high electrical conductivity, high output voltages, and high volumetric capacity density. However, an important problem, termed the "shuttle effect", can lead to capacity decay in Li-Se cells (and in Li-S cells), which arises from aggregation and the loss of Se or S from the cathode into the electrolyte. In this work, in order to solve this problem, a new self-repairing system has been devised, in which some Se atoms are chemically bonded to the carbon atoms of graphene and act as reclaiming points for dissociated Se atoms through the establishment of -Se-Se-Se- chains. Se-decorated graphene (Se-GE) was first constructed through a facile high-energy ball-milling process. Its formation was confirmed by XRD, SEM, HRTEM, XPS, and Raman analyses. As we anticipated, in examining cell properties, the as-prepared Se-GE composite underwent an initial capacity decay in the first 20 cycles (from 1050 mAh g-1 to 750 mAh g-1 , ca. 29 % loss), but the capacity then reverted to 970 mAh g-1 (ca. 92 % of the initial value). Other measurements were also consistent with the recapture of dissociated Se atoms.

The construction of semiconductor composites is known as a powerful method used to realize the spatial separation of electrons and the holes in them, which can result in more electrons or holes and increase the dispersion of oxygen ions ( and O − ) (one of the most critical factors for their gas-sensing properties) on the surface of the semiconductor gas sensor. In this work, using 1D ZnO/ZnSnO3 nanoarrays as an example, which are prepared through a hetero-epitaxial growing process to construct a chemically bonded interface, the above strategy to attain a better semiconductor gas-sensing property has been realized. Compared with single ZnSnO3 nanotubes and no-matching ZnO/ZnSnO3 nanoarrays gas sensors, it has been proven by x-ray photoelectron spectroscopy and photoluminescence spectrum examination that the as-obtained ZnO/ZnSnO3 sensor showed a greatly increased quantity of active surface electrons with exceptional responses to trace target gases and much lower optimum working temperatures (less than about 170 °C). For example, the as-obtained ZnO/ZnSnO3 sensor exhibited an obvious response and short response/recovery time (less than 10 s) towards trace H2S gas (a detection limit down to 700 ppb). The high responses and dynamic repeatability observed in these sensors reveal that the strategy based on the as-presented electron and hole separation is reliable for improving the gas-sensing properties of semiconductors.