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Urea electrolysis can be used to treat wastewater containing urea and alleviate the energy crisis, so it is one of the best ways to solve environmental and energy problems. This paper reports the synthesis of M doped NiVS (M = Co, Ce and Cr) composites by a simple hydrothermal process for the first time. What is noteworthy is that the Ce-NiVS material as a catalytic electrode requires only 141 mV overpotential for the hydrogen evolution reaction (HER) and 1.291 V potential for the urea oxidation reaction (UOR) at a current density of 10 mA cm−2 in 1.0 M KOH and 0.5 M urea mixed alkaline solution. Using Ce-NiVS/NF as both the anode and cathode for urea electrolysis, a current density of 10 mA cm−2 is driven by a voltage of only 1.55 V, which is better than most previous catalysts. Experimental results demonstrate that the excellent catalytic activity of Ce-NiVS materials is due to the formation of a large number of active sites and the improvement of conductivity due to doping with Ce. Density functional theory calculation shows that the VS4 material has a small Gibbs free energy of hydrogen adsorption, which plays a major role in the hydrogen production process, and Ce-NiS has a higher density of states (DOS) near the Fermi level, indicating that Ce-NiS has better electronic conductivity. The synergistic catalysis of VS4 and Ce-NiS promoted the hydrogen production performance of the Ce-NiVS material. This work provides guidance for the optimization and design of low-cost electrocatalysts to replace expensive precious metal-based electrocatalysts for overall urea electrolysis. [ABSTRACT FROM AUTHOR]

Porphyrins have been widely used in designing photocatalyst systems. However, finding an effective strategy to improve the intrinsic photocatalytic activity of porphyrin molecules remains a challenge. Here, two new porphyrins, meso-tetra(5-carboxyfuryl)porphyrin (H2TCFP) and meso-tetra(5-carboxythienyl)porphyrin (H2TCTP), were successfully synthesized and compared with meso-tetra(m-carboxyphenyl)porphyrin (H2TmCPP), to clarify the influence of the organic unit bridging the carboxyl acid group with the porphine ring on the photocatalytic activity of porphyrin for H2 evolution from water splitting. The H2 evolution rates of 10.8 mmol g−1 h−1 observed for H2TCFP and 9.7 mmol g−1 h−1 for H2TCTP are both larger than 8.0 mmol g−1 h−1 observed for H2TmCTP under optimal conditions. The best photocatalytic activity observed for H2TCFP was investigated through experiments and density functional theory (DFT) calculations and was interpreted in terms of the combined effect of several key factors of the entire photocatalytic process, including the high absorptivity of UV light, high separation efficiency of photogenerated carriers, and low Gibbs energy required for associated water splitting. Meanwhile, the concentration-dependent performance of photocatalytic activity was analyzed and attributed to the aggregation and light-bleaching effect exerted on porphyrins. [ABSTRACT FROM AUTHOR]

The electronic state of metallic centers plays a crucial role in electrocatalytic reactions such as oxygen evolution reaction (OER), which usually require high-valence transition metallic centers. Herein, we propose an organic ligand coordination strategy to modulate the electronic state of metallic centers in NiFe LDH, by introducing three different organic linkers including 2,6-naphthaleneducarboxylic acid, 4,4′-bipyridine, and 1H-1,2,3-triazole on the surface of NiFe LDH to derive atomic-layered metal–organic framework (NiFe LDH@MOF). Experimental results indicate that the electronic structure of metal centers in the composite was modified after the coordination of organic linker, among which the most amount of high-valence state was for Fe species in the 1H-1,2,3-triazole involved catalysts (NiFe LDH@MOF-3). Density functional theory (DFT) calculations further demonstrate that the 1H-1,2,3-triazole linkers around Fe centers optimized the d-band center together with the beneficial Gibbs free energy of the intermediate. Therefore, NiFe LDH@MOF-3 exhibited a superior electrocatalytic OER performance with a low overpotential of 242 mV to achieve a current density of 100 mA cm−2, a small Tafel slope of 32.3 mV dec−1. This work provides a general strategy for the modulation of the electronic structure of metallic centers using organic linker coordination to achieve a high-performance electrocatalyst. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting as an important means of obtaining high purity hydrogen fuel has attracted great interest. In this study, the structural engineering of complex WNiM–WNi LDH (M = Se, S, or P) was firstly developed by in situ growth on Ni foam for use in overall water splitting and the urea oxidation reaction. These WNiM–WNi LDH (M = Se, S, or P) catalysts exhibit outstanding electrocatalytic performance in the hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and urea oxidation reaction (UOR), respectively. An overpotential of only 64 mV of OER is required for WNiS–WNi LDH and 126 mV of HER is required for WNiP–WNi LDH to achieve 10 mA cm−2. The WNiSe–WNi LDH materials display a particularly outstanding performance for UOR, requiring a potential of 1.25 V to drive 10 mA cm−2. Moreover, the optimized WNiS–WNi LDH as an anode and WNiP–WNi LDH as a cathode can achieve 10 mA cm−2 at a low cell voltage of 1.45 V in 1 M KOH solution for overall water splitting. The density functional theory calculations show that the introduction of the NiP2 and WP material greatly reduces the Gibbs free energy of the hydrogen adsorption of the material. [ABSTRACT FROM AUTHOR]

The development of earth-rich, low-cost, and high-efficiency electrocatalysts toward alkaline hydrogen evolution reactions (HERs) in the water spitting process is extremely desirable yet a huge challenge. In this work, we report the synthesis of novel RuO2/MoS2 electrocatalysts with good conductivity and abundant active sites for efficient HER by uniformly dispersing RuO2 nanoparticles on MoS2 nanosheets. Benefitting from the intense electronic coupling effect endowed with interface modifications, the as-prepared RuO2/MoS2 electrocatalysts exhibited superior performance for HER in 1 M KOH with a very low overpotential of 36 mV at 10 mA cm−2 and a small Tafel slope value of 34.8 mV dec−1. Moreover, the introduction of RuO2 nanoparticles improved the durability of the RuO2/MoS2 electrocatalysts with negligible variation in a 20 h operation. More importantly, the density functional theory (DFT) calculations further revealed the mechanism of strong electronic interaction between RuO2 nanoparticles and MoS2 nanosheets, which contributes to accelerating the H2O dissociation kinetics and optimizing H adsorption Gibbs free energy. This work may provide a deeper understanding for designing efficient HER catalysts through interface modification strategies. [ABSTRACT FROM AUTHOR]

The construction of an efficient non-noble-metal electrocatalyst towards alkaline hydrogen evolution is challenging but in great demand. The fabrication of a porous nanostructure and heteroatom doping are two productive strategies for developing effective electrocatalysts. In this contribution, we report the preparation of La, Ce and Er-doped Ni2P porous nanostructures through a facile water bath method and phosphorization strategy. The Er-doped Ni2P porous nanostructure exhibits superb hydrogen evolution reaction (HER) catalytic performance under alkaline conditions with a low cathodic overpotential of 87 mV (10 mA cm−2, glassy carbon) and a small Tafel slope of 65.4 mV dec−1. It also displays excellent electrochemical stability in alkaline electrolytes. First-principles density functional theory (DFT) calculations disclosed the mechanism of the alkaline HER catalysis. For pristine Ni2P, the P site acts as the optimal active site with the Gibbs free energy of H* absorption (ΔGH*) of 0.48 eV. After La, Ce and Er are doped, respectively, the P site is still the active center of the three doping systems. Notably, the ΔGH* value is reduced from 0.48 eV to 0.23 eV (P site in La-doped Ni2P), 0.20 eV (P site in Ce-doped Ni2P) and 0.18 eV (P site in Er-doped Ni2P), suggesting that doping with La, Ce and Er atoms plays a crucial role in decreasing the H* absorption energy on optimal P sites and the optimum active site with a smaller ΔGH* can expedite the charge transfer rate for H* midbody and H2 generation. This is particularly noticeable for Er doping, which is in accordance with the experimental result. [ABSTRACT FROM AUTHOR]