Atomically Dispersed Silver Atoms Embedded in NiCo Layer Double Hydroxide Boost Oxygen Evolution Reaction.

Bimetallic layered double hydroxides (LDHs) are promising catalysts for anodic oxygen evolution reaction (OER) in alkaline media. Despite good stability, NiCo LDH displays an unsatisfactory OER activity relative to the most robust NiFe LDH and CoFe LDH. Herein, a novel NiCo LDH electrocatalyst modified with single-atom silver grown on carbon cloth (AgSA -NiCo LDH/CC) that exhibits exceptional OER activity and stability in 1.0 m KOH is reported. The AgSA -NiCo LDH/CC catalyst only requires a low overpotential of 192 mV to reach a current density of 10 mA cm-2 , obviously boosting the OER activity of NiCo LDH/CC (410 mV@10 mA cm-2 ). Inspiringly, AgSA -NiCo LDH/CC can maintain its high activity for up to 500 h at a large current density of 100 mA cm-2 , exceeding most single-atom OER catalysts. In situ Raman spectroscopy studies uncover that the in situ formed NiCoOOH during OER is the real active species. Hard X-ray absorption spectrum (XAS) and density functional theory (DFT) calculations validate that single-atom Ag occupying Ni site increases the chemical valence of Ni elements, and then weakens the adsorption of oxygen-contained intermediates on Ni sites, fundamentally accounting for the enhanced OER performance.

Modulating the Electronic Structure of Nickel Sulfide Electrocatalysts by Chlorine Doping toward Highly Efficient Alkaline Hydrogen Evolution.

The exploration of indurative and stable low-cost catalysts for hydrogen evolution reaction (HER) is of great importance for hydrogen energy economy, but it still faces challenges. Herein, we report a Cl-doped Ni3S2 (Cl-Ni3S2) nanoplate catalyst vertically grown on Ni foam with outstanding activity and durability for HER, which only requires an overpotential of 67 mV to reach a current density of 10 mA cm-2 in alkaline media and exhibits negligible degradation after 30 h of operation. Both the advanced X-ray absorption fine structure (XAFS) and density functional theory (DFT) calculation validate that Cl doping can optimize the electronic structure and the intrinsic activity of Ni3S2. This study devoted to the revelation of the impact of ionic doping on the activity of catalysts at the atomic scale can provide the direction for the rational design of novel and advanced HER electrocatalysts.

Boron Coordination Effect in Ni-Nx Doped Graphene Catalysts on the ORR Performance Based on DFT Calculations.

The coordination atoms of metal active site in transition metal N-doped carbon single atom electrocatalysts play a vital role in dominating the catalytic performance of oxygen reduction reaction (ORR) at the cathode of fuel cells or metal-air cells. In view of weak adsorption ability of Ni active site in NiN4 -C catalysts to oxygen intermediate states, herein we introduce boron atoms with smaller electronegativity than N and C atoms to modulate the local coordination environment and electronic structures of Ni site. First-principles density functional calculations reveal that both B substitution for N atoms (NiN2 B2 -C) and B coordinating with N and C (NiN4 B8 -C) can effectively optimize the Gibbs free energy of oxygen intermediate states and hence improve the catalytic activity of the materials. In addition, we propose that the trend change in catalytic activity is mainly governed by the filling of antibonding orbitals between Ni-3d and O-2p states near the Fermi level.

Engineering sulfur vacancies into Fe9S10 nanosheet arrays for efficient alkaline hydrogen evolution.

The development of Earth-abundant transition metal sulfide electrocatalysts with excellent activity and stability toward the alkaline hydrogen evolution reaction (HER) is critical but challenging. Iron-based sulfides are favored due to their economic benefits and good stability, but their intrinsic catalytic activity still needs to be improved urgently. Herein, we successfully prepared Fe9S10 nanosheet arrays on iron foam (Fe9S10/IF) through a simple one-step method and utilized plasma treatment to introduce S vacancies (Fe9S10-Vs/IF) to regulate their intrinsic catalytic activity. The final materials demonstrate excellent HER performance, and only need 149 mV to drive a current density of 10 mA cm-2 and a small Tafel slope of 50 mV dec-1. The experimental results show that the existence of S vacancies can enhance their intrinsic electrocatalytic activity. This work provides a reference value for the future regulation of iron-based sulfides and is devoted to the development of non-precious metal catalysts toward the HER.

Designing Zn-doped nickel sulfide catalysts with an optimized electronic structure for enhanced hydrogen evolution reaction.

Designing non-noble-metal electrocatalysts with excellent performance and economic benefits toward the hydrogen evolution reaction (HER) is extremely crucial for future energy development. In particular, the rational cationic-doped strategy can effectively tailor the electronic structure of the catalysts and improve the free energy of the adsorbed intermediate, thus enhancing HER performance. Herein we reported Zn-doped Ni3S2 nanosheet arrays supported on Ni foam (Zn-Ni3S2/NF) that were synthesized by a two-step hydrothermal process for improving HER catalysis under alkaline conditions. Remarkably, the obtained Zn-Ni3S2/NF displays excellent HER catalytic performance with an overpotential of 78 mV to reach a current density of 10 mA cm-2 and dramatic long-term stability for 18 h in 1 M KOH. In addition, the results based on the density functional theory calculations reveal that Zn dopants can modulate the electronic structure of Ni3S2 and optimize the hydrogen adsorption free energy (ΔGH*). Thus cationic-doping engineering provides an efficient method to enhance the intrinsic activities of transition-metal sulfides, which may contribute to the development of nonprecious electrocatalysts for HER.

Engineering Bimetallic NiFe-Based Hydroxides/Selenides Heterostructure Nanosheet Arrays for Highly-Efficient Oxygen Evolution Reaction.

Developing cost-effective and high-efficiency electrocatalysts toward alkaline oxygen evolution reaction (OER) is crucial for water splitting. Amorphous bimetallic NiFe-based (oxy)hydroxides have excellent OER activity under alkaline media, but their poorly electrical conductivity impedes the further improvement of their catalytic performance. Herein, a bimetallic NiFe-based heterostructure electrocatalyst that is composed of amorphous NiFe(OH)x and crystalline pyrite (Ni, Fe)Se2 nanosheet arrays is designed and constructed. The catalyst exhibits an outstanding OER performance, only requiring low overpotentials of 180, 220, and 230 mV at the current density of 10, 100, and 300 mA cm-2 and a low Tafel slope of 42 mV dec-1 in 1 m KOH, which is among the state-of-the-art OER catalysts. Based on the experimental and theoretical results, the electronic coupling at the interface that leads to the increased electrical conductivity and the optimized adsorption free energies of the oxygen-contained intermediates plays a crucial role in enhancing the OER activities. This work focusing on improving the OER performance via engineering amorphous-crystalline bimetallic heterostructure may provide some inspiration for reasonably designing advanced electrocatalysts.

Al-doped nickel sulfide nanosheet arrays as highly efficient bifunctional electrocatalysts for overall water splitting.

The development of low-cost, high-activity, durable non-precious metal bifunctional electrocatalysts is of great importance in the production of hydrogen by water electrolysis. In this work, we have prepared new Al-doped Ni3S2 nanosheet arrays grown on Ni foam (Al-Ni3S2/NF) as an excellent bifunctional electrocatalyst in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The Al-Ni3S2/NF electrode obtained only requires extremely low overpotentials of 86 and 223 mV for the HER and OER to achieve a current density of 10 mA cm-2 in 1 M KOH, respectively. Moreover, the electrolytic cell assembled using this electrode as both cathode and anode provides a current density of 10 mA cm-2 at an extremely low battery voltage of 1.58 V relative to that with Ni3S2/NF (1.71 V). Additionally, both experimental results and theoretical calculations reveal that the increased electrochemical active surface area and optimized intermediate adsorption free energies are responsible for the enhanced electrocatalytic performance. This work provides a promising bifunctional electrocatalyst for water electrolysis in alkaline media with broad application prospects.

Interface engineering of Ag-Ni3S2 heterostructures toward efficient alkaline hydrogen evolution.

Exploring Earth-abundant transition-metal-based electrocatalysts with high performance toward the alkaline hydrogen evolution reaction (HER) is crucial for sustainable hydrogen production. Ni3S2 has been recently identified as a promising HER catalyst, but it has unfavorable water dissociation and hydrogen adsorption characteristics. Here, we report Ag-decorated Ni3S2 nanosheet arrays grown on Ni Foam (NF) (Ag-Ni3S2/NF) as efficient heterostructure electrocatalysts for the HER in alkaline media. The catalyst only requires a low overpotential of 89 mV at 10 mA cm-2, as well as sustaining long-term durability for 15 h. The experimental analysis, in combination with density functional theory calculation, demonstrates that the electronic coupling at the interface between Ni3S2 and Ag results in enhanced electronic conductivity and optimized hydrogen adsorption and water adsorption/dissociation free energies. This work not only develops a highly efficient catalyst toward the HER, but also sheds light on the structure-activity relationship of the heterostructure catalyst on an atomic scale.

P-Doped Iron-Nickel Sulfide Nanosheet Arrays for Highly Efficient Overall Water Splitting.

Iron-nickel sulfide ((Ni,Fe)3S2) is one of the most promising bifunctional electrocatalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media because of their metallic conductivity and low cost. However, the reported HER activity of (Ni,Fe)3S2 is still unsatisfactory. Herein, three-dimensional self-supported phosphorus-doped (Ni,Fe)3S2 nanosheet arrays on Ni foam (P-(Ni,Fe)3S2/NF) are synthesized by a simple one-step simultaneous phosphorization and sulfuration route, which exhibits dramatically enhanced HER activity as well as drives remarkable OER activity. The incorporation of P significantly optimized the hydrogen/water absorption free energy (ΔGH*/ΔGH2O*), enhanced electrical conductivity, and increased electrochemical surface area. Accordingly, the optimal P-(Ni,Fe)3S2/NF exhibits relatively low overpotentials of 98 and 196 mV at 10 mA cm-2 for HER and OER in 1 M KOH, respectively. Furthermore, an alkaline electrolyzer comprising the P-(Ni,Fe)3S2/NF electrodes needs a very low cell voltage of 1.54 V at 10 mA cm-2 and exhibits long-term stability and outperforms most other state-of-the-art electrocatalysts. The reported electrocatalyst activation approach by anion doping can be adapted for other transition-metal chalcogenides for water electrolysis, offering great promise for future applications.

Ultrafast fabrication of nickel sulfide film on Ni foam for efficient overall water splitting.

Development of low-cost, high performance and stable non-noble electrocatalysts with both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities for overall water splitting is essential for future energy supply. Herein, for the first time, a facile and ultrafast synthetic method has been reported to fabricate nickel sulfide (Ni3S2) films on Ni foam (Ni3S2/NF) as efficient bifunctional electrodes for overall water splitting through direct dropping of mercaptoethanol solution followed by annealing at 300 °C for only 50 s. Thanks to the integrated three-dimensional (3D) configuration, the obtained Ni3S2/Ni foam exhibits excellent activity and stability for HER and OER with low overpotentials of 131 and 312 mV, respectively, to attain a current density of 10 mA cm-2 in alkaline media. Ni(OH)x species formed on the Ni3S2 surface serves as the actual catalytic site during OER reaction. Given the well-defined bifunctionality, an overall water-splitting device using two identical Ni3S2/NF electrodes delivers a current density of 10 mA cm-2 at a low cell voltage of 1.68 V in an alkaline water electrolyzer. This approach is promising as a simple method for depositing a wide range of useful transition metal sulfide electrocatalysts on corresponding metal substrate bifunctional electrodes for overall water splitting, shedding some light on the development of functional materials in energy chemistry.

High-Switching-Ratio Photodetectors Based on Perovskite CH3NH3PbI3 Nanowires.

Hybrid organic-inorganic perovskite materials have attracted extensive attention due to their impressive performance in photovoltaic devices. One-dimensional perovskite CH3NH3PbI3 nanomaterials, possessing unique structural features such as large surface-to-volume ratio, anisotropic geometry and quantum confinement, may have excellent optoelectronic properties, which could be utilized to fabricate high-performance photodetectors. However, in comparison to CH3NH3PbI3 thin films, reports on the fabrication of CH3NH3PbI3 nanowires for optoelectrical application are rather limited. Herein, a two-step spin-coating process has been utilized to fabricate pure-phase and single-crystalline CH3NH3PbI3 nanowires on a substrate without mesoporous TiO2 or Al2O3. The size and density of CH3NH3PbI3 nanowires can be easily controlled by changing the PbI2 precursor concentration. The as-prepared CH3NH3PbI3 nanowires are utilized to fabricate photodetectors, which exhibit a fairly high switching ratio of ~600, a responsivity of 55 mA/W, and a normalized detectivity of 0.5 × 1011 jones under 532 nm light illumination (40 mW/cm²) at a very low bias voltage of 0.1 V. The as-prepared perovskite CH3NH3PbI3 nanowires with excellent optoelectronic properties are regarded to be a potential candidate for high-performance photodetector application.

Determination of the basic optical parameters of ZnSnN(2).

Polycrystalline ZnSnN(2) thin films were successfully prepared by DC magnetron sputtering at room temperature. Both the as-deposited and annealed films showed n-type conduction, with electron concentration varying between 1.6×10(18) and 2.3×10(17) cm(-3) and the maximum mobility of 3.98 cm(2) V(-1) s(-1). The basic optical parameters such as the refraction index, extinction coefficient, and absorption coefficient were precisely determined through the spectroscopic ellipsometry measurement and analysis. The optical bandgap of the ZnSnN(2)films was calculated to around 1.9 eV, with the absorption coefficient greater than 10(4) cm(-1) at wavelengths less than 845 nm. The easy-fabricated ZnSnN(2) possesses a sound absorption coefficient ranging from the ultraviolet through visible light and into the near-infrared, comparable to some typical photovoltaic materials such as GaAs, CdTe, and InP.