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Substituting slow oxygen evolution reaction (OER) with thermodynamically favorable urea oxidation reaction (UOR) is considered as one of the feasible strategies for achieving energy-saving hydrogen production. Herein, a uniform layer of NiMoO4 nanorods was grown on nickel foam by a hydrothermal method. Then, a series of Ni-MoOx/NF-X nanorod catalysts comprising Ni/NiO and MoOx (MoO2/MoO3) were prepared through regulating annealing atmosphere and reduction temperature. The optimized Ni-MoOx/NF-3 with a large accessible specific area can act as a bifunctional catalyst for electrocatalytic anodic UOR and cathodic hydrogen evolution reaction (HER). At a current density of 100 mA cm−2, the introduction of urea can significantly reduce the overpotential of Ni-MoOx/NF-3 by 210 mV compared to OER. In addition, Ni-MoOx/NF-3 has a higher intrinsic activity than other catalysts. It only requires −0.21 and 1.38 V to reach 100 mA cm−2 in HER and UOR, respectively. Such an excellent performance can be attributed to the synergistic function between Ni and MoOx. The presence of metallic Ni and reduced MoOx in pairs is beneficial for improving the electrical conductivity and modulating the electronic structure, resulting in enhancing the electrocatalytic performance. When assembling Ni-MoOx/NF-3 into an overall urea–water splitting system, it can achieve energy-saving hydrogen production and effective removal of urea-rich wastewater. [ABSTRACT FROM AUTHOR]

Electrochemical-phosphorization as a cost-effective and ecofriendly approach is proposed to fabricate an amorphous Ni–P shell partially covering the surface of ordered porous Ni (p-Ni) for the first time. The obtained Ni–P/p-Ni shows superior catalytic activity for the hydrogen evolution reaction (HER), compared with the Ni2P/p-Ni prepared by a traditional solid-phosphorization process at high temperature. Such enhanced catalytic activity for the Ni–P/p-Ni is contributed to by the high intrinsic activity from a synergistic effect of amorphous Ni–P and the neighbouring nickel containing hydroxides/oxides. [ABSTRACT FROM AUTHOR]

Using urea oxidation reaction (UOR) instead of oxygen evolution reaction (OER) is one of promising strategies for significantly diminish power consumption for hydrogen production from electrochemical water splitting. The electrocatalysts with cost-effective, multifunctional and high-performance are urgently required for enhancing UOR and hydrogen evolution reaction (HER), but this remains a challenge. Herein, we designed a bifunctional Ni(OH) x /p-Ni catalyst by electrochemical oxidation of Ni(OH) 2 in-situ grown on the surface of porous Ni membrane (p-Ni) to generate more abundant high-valence Ni3+ active species, which is favorable for reducing the energy barrier of electrochemical reaction. At the same time, a large number of metallic oxygen bonds (Ni–O) were formed to optimize the reaction kinetics of the electrochemical process, thus promoting the overall urea electrolysis efficiency. In 1.0 M KOH with 0.3 M urea, the optimized Ni(OH) x /p-Ni only requires potentials of 1.38 V and 0.22 V to obtain a current density of 100 mA cm−2 for UOR and HER, respectively. Notably, by assembling the Ni(OH) x /p-Ni as the cathode and anode for hydrogen production from urea-assisted water splitting, it can drive a current density of 100 mA cm−2 at a low voltage of 1.52 V and has excellent stability. This work provides a feasible strategy for design efficiently non-noble metal electrocatalysts for energy-saving hydrogen production and purifying urea-rich wastewater. [Display omitted] • Nanoflowers Ni(OH) 2 /p-Ni was grown on porous Ni membrane by solvthremal oxidation. • Electrochemical oxidation in-situ generates abundant Ni3+ active species. • The Ni(OH) x /p-Ni exhibited excellent bifunctional performance for HER/UOR. • Replacing OER with UOR can significantly save energy for hydrogen production. [ABSTRACT FROM AUTHOR]

A thin-layer of Ni(OH) 2 was in situ formed on the surface of Ni 2 P nanopillars (Ni(OH) 2 @Ni 2 P/E-NF) via a facile hydrothermal treatment in H 2 O. Ni(OH) 2 @Ni 2 P/E-NF exhibits superior activity for the hydrogen evolution reaction with an overpotential of only 43 mV to achieve 10 mA cm −2 and a good durability during the long-term operation in an alkaline medium. The excellent performance of Ni(OH) 2 @Ni 2 P/E-NF is likely ascribed to the strong interfacial coupling of Ni(OH) 2 and Ni 2 P, which promotes the dissociation of water and concomitantly converts hydrogen intermediates (H ad ) to H 2 . [ABSTRACT FROM AUTHOR]

Hydrogen production from water splitting is a green and efficient technology for storing clean energy. Herein, cerium-incorporated Ni 2 P nanosheets are designed as trifunctional electrocatalysts to generate hydrogen by hydrothermal self-oxidation of surface nickel foam (NF) in pure water to in-situ form Ni(OH) 2 nanosheets, followed by incorporation of Ce and phosphorization. The prepared material exhibits excellent electrocatalytic performance in hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and urea oxidation reaction (UOR). When the current density is 100 mA cm−2, the UOR potential of Ce-Ni 2 P is 1.473 V lower than that in the OER (1.731 V), suggesting a great potential to replace the sluggish OER for overall water splitting. Moreover, the Ce-Ni 2 P/NF can be applied to the electrochemical treatment of real urine electrolysis with similar performance to the urea electrolysis. Such remarkable performance is attributed to the incroporation of Ce with "Ce3+/Ce4+ redox pairs", which can not only provide abundant reactive sites by the charge transfer appearance of defect sites, but also offer an effective buffering space for the pre-oxidation process from Ni2+ to Ni3+. It is thus beneficial for overall water splitting and coupled urea electrolysis, providing a promising candidate for urine wastewater treatment and clean energy production. • Nanosheets are prepared by hydrothermal self-oxidation of NF in pure water. • Ce leads to the lattice distortion of Ce-Ni2P and generates abundant defects. • Such interactions between Ce and Ni2P promote HER and OER/UOR performance. • Ce-Ni2P/NF can be applied for urine wastewater treatment. [ABSTRACT FROM AUTHOR]

We report a novel fabrication of nickel-molybdenum alloy nanorods catalyst for hydrogen evolution reaction (HER), which is prepared by co-deposition of pure nickel and molybdenum in a multisource sputtering system on the surface of Ni foam substrate. The Ni–Mo alloy film exhibits favorable vertical nanorods structure and presents the most efficient activity for HER compared to the film only including one metal element. The remarkably enhanced catalytic activity is attributed to its ordered array geometry as well as the synergistic interaction between Ni and Mo. Meanwhile, the open space within nanorod arrays facilitates the electrolyte penetration and diffusion of ionic species, allowing high utilization efficiency of active species as well as rapidly release of evolved hydrogen gas from the electrode surface. [ABSTRACT FROM AUTHOR]

• 2D interconnected NiTe/NF nanosheets was prepared by one-step hydrothermal method. • Annealing temperatures have an effect on crystal phase change and HER performance. • It leads to a positive shift of the d-band center on non-stoichiometric Ni 2.86 Te 2. • The Ni 2.86 Te 2 /NF exhibits superior HER performance compared to NiTe/NF. The non-stoichiometric Ni 2.86 Te 2 /NF was prepared by hydrothermal method combined with annealing process. Experimental and theoretical results demonstrate that the transition of crystal phase structure from NiTe to Ni 2.86 Te 2 leads to a strong electronic interaction between tellurium and nickel accompanying with the positive shift of the d-band center, resulting in improving the HER activity compared to the NiTe/NF. [Display omitted] It is of great significance to develop low cost, high-efficiency and environment-friendly electrocatalysts for hydrogen evolution reaction (HER) from water splitting. Herein, nickel telluride nanosheets grown on Ni Foam (NF) with three different crystal phases (NiTe, Ni 2.6 Te 2 and Ni 2.86 Te 2) are fabricated by one-step hydrothermal tellurization followed annealing process. The non-stoichiometric Ni 2.86 Te 2 /NF exhibits superior electrocatalytic HER performance compared to the NiTe/NF and Ni 2.6 Te 2 /NF, which is comparable to the state-of-the-art 20 wt% Pt/C catalyst at high current density. The Ni 2.86 Te 2 /NF only requires an overpotential of 348 mV to drive the current density of 200 mA cm−2 in a 1.0 M KOH electrolyte. Similarly, The Ni 2.86 Te 2 /NF delivered current densities of 200 mA cm−2 at the overpotential of 279 mV in 0.5 M H 2 SO 4. Such excellent performance could be ascribed to the fast electron transfer and positive shift of d d-band center from its rich defective effect of crystal phase transition, as well as to the exposure of active sites provided by the two-dimensional nanosheets with large specific surface area. This work provides valuable insights for the rational modulation of the crystal phase on the nickel telluride for catalyzing HER. [ABSTRACT FROM AUTHOR]

Efficient hydrogen production by water electrolysis is primarily restrained by imperfect over-potential and poor reaction dynamics on oxygen evolution reaction (OER). Thermodynamically favourable urea oxidation reaction (UOR) is a class of promising routes for substituting sluggish OER and for coupling with cathodic hydrogen production because of smaller equilibrium potential (0.37 V) than that of OER (1.23 V). Herein, a versatile Ru-NiO/p-Ni catalyst was prepared through in-situ generating nickel hydroxide nanosheets on the surface of ordered porous Ni, then doping low Ru and annealing treatment. The optimized Ru-NiO/p-Ni displayed outstanding activity and stability towards hydrogen evolution reaction (HER), OER and UOR with potentials of −0.13 V, 1.57 V, and 1.39 V at 100 mA cm−2, respectively. Ru-NiO/p-Ni‖Ru-NiO/p-Ni can achieve 100 mA cm−2 in urea-aided water splitting at a voltage of only 1.58 V, which is prominently 170 mV smaller than the voltage of water electrolysis (1.75 V). The excellent electrocatalytic performance is owing to the outstanding inherent activity generated by cooperative effect of Ru and NiO, along with rich defect and active centre of Ru-NiO/p-Ni supplied by the large surface area of 3D porous structure. The formation of more rich Ni active species with a high valence through transport of electrons between Ru and Ni is favourable to promoting the dissociation of urea molecules, eventually improving UOR. Therefore, it can facilitate urea-aided water splitting, which provides a valuable strategy for constructing versatile catalysts for a cathodic energy-efficient hydrogen production coupled with other anodic oxidation reactions. [Display omitted] • Replacing OER with UOR is apparently energy-saving for hydrogen production. • Ru activates NiO nanosheets grown in-situ on porous Ni to obtain more active sites. • Electron transfers of Ru and Ni species significantly promotes HER/OER/UOR. [ABSTRACT FROM AUTHOR]

Designing highly active and durable catalysts is considered to be crucial for enhancing hydrogen evolution reaction (HER) from water electrolysis. Although some studies indicate that anatase TiO 2 is a promising candidate for electrolytic hydrogen evolution reaction, the influence of different crystalline phases of TiO 2 on the supported Ru catalysts for electrocatalytic HER performance is rarely systematically explored. Herein, a series of Ru/TiO 2 -X (X = R (Rutile), A (Anatase), and P25) catalysts were prepared to investigate the influence of the rutile and anatase phases of TiO 2 on the catalytic activity of Ru catalysts in HER. The findings demonstrate that the HER activity is much affected by the variation of the titania structure, when other factors are kept constant. The 15Ru/TiO 2 -R-H 2 has superior HER performance with a small overpotential of 63 mV to achieve a current density of 10 mA cm−2 in acidic electrolyte and 99 mV in alkaline electrolyte compared to 15Ru/TiO 2 -A-H 2 and 15Ru/TiO 2 -P25-H 2. This might be attributed to the faster electron transfer and lower Fermi level caused by the oxygen vacancy (V O) and strong metal-support interaction (SMSI), along with the exposure of active sites afforded by the highly dispersed ruthenium nanoparticles on the rutile TiO 2. Our results indicate that the presence of rutile TiO 2 support alone is adequate to maintain Ru in its most active form and make it a more performing catalyst, compared to anatase titania and P25. • Ru is supported on different crystalline phase of TiO 2 for electrocatalytic HER. • Partial Ru is incorporated the lattice of TiO 2 -R with SMSI effect. • Highly dispersed Ru and rich V O promote electrocatalytic HER. • Electron transfer from V O and Ti to surface Ru is conducive to optimizing HER. [ABSTRACT FROM AUTHOR]

Herein, a "chimney effect" formed on the interface between the metal oxide and nickel metal for the hydrogen evolution reaction is confirmed by using density functional theory calculations and experimental methods. • A "chimney effect" formed on the interface between the metal oxide and nickel metal for the hydrogen evolution reaction is found. • The "chimney effect" is a result of the interfacial charge transfer between the metal and metal oxide. • The chemical environment around interface makes the neighboring sites be immune to H 2 O* and OH* adsorption but tend to adsorb H* selectively. • The metal oxide/metal interface is beneficial for the smooth adsorption of H* and the easy desorption of H 2 from the catalyst surface. • Experiments further reveal the key role of the amount of chimney, i.e., the interfacial metal atoms, for the excellent HER activity. Precise atomic-level control of composition and geometric structure at the interface between two catalyst components can effectively tune the catalytic properties. Herein, we found a "chimney effect" formed on the interface between the metal oxide and Nickel metal for the hydrogen evolution reaction, using density functional theory calculations and experimental methods. This special chemical environment around the interface leads the neighboring sites to be immune to the H 2 O* and OH* adsorption and to only selectively adsorb H* properly. Meanwhile, it is also beneficial for the smooth adsorption of the reactant (H*) on the interface and the easy desorption of the product (H 2) from the catalyst surface (ΔG H* close to zero). This phenomenon appears similar to a chimney of hydrogen evolution around the metal oxide/metal interface. Such "chimney effect" is a result of the interfacial charge transfer between the metal and metal oxide, and should be the nature of the interface-induced synergistic effect in metal oxide/metal composite catalysts for HER. Experiments further confirm that the catalytic activity of metal oxide/metal composites for HER can be enhanced by increasing the amount of the chimney - the interfacial metal atoms. [ABSTRACT FROM AUTHOR]