Nickel sulfide and phosphide electrocatalysts for hydrogen evolution reaction: challenges and future perspectives

The search for environmentally friendly and sustainable energy sources has become necessary to alleviate the issues associated with the consumption of fossil fuel such as air pollution and global warming. Furthermore, this is significant considering the exhaustible resources and burgeoning energy demand globally. In this regard, hydrogen, a clean fuel with high energy density, is considered a reliable alternative energy source. The hydrogen evolution reaction (HER) is one of the most promising methods to produce green hydrogen from water on a large scale. However, the HER needs effective electrocatalysts to address the concerns of energy consumption; thus, finding active materials has recently been the main focus of researchers. Among the various electrocatalysts, nickel sulfides and phosphides and their derivatives with low cost, high abundance, and relatively straightforward preparation have shown high HER activity. In this review, we compare the diverse methods in the synthesis of nickel sulfides and phosphides together with effective synthesis parameters. Also, the optimum conditions for the preparation of the desired active materials and their properties are provided. Then, the performance of nickel sulfide and phosphide electrocatalysts in the HER is addressed. The HER activity of the various crystalline phases is compared, and their most active crystalline phases are introduced. Finally, the present challenges and perspectives for future HER electrocatalysts are presented.

Phase-Controllable Growth Nix Py Modified CdS@Ni3 S2 Electrodes for Efficient Electrocatalytic and Enhanced Photoassisted Electrocatalytic Overall Water Splitting

The rational design and construction of cost-effective nickel-based phosphide or sulfide (photo)electrocatalysts for hydrogen production from water splitting has sparked a huge investigation surge in recent years. Whereas, nickel phosphides (Ni_x P_y ) possess more than ten stoichiometric compositions with different crystalline. Constructing Ni_x P_y with well crystalline and revealing their intrinsic catalytic mechanism at atomic/molecular levels remains a great challenge. Herein, an easy-to-follow phase-controllable phosphating strategy is first proposed to prepare well crystalline Ni_x P_y (Ni₃ P and Ni₁₂ P₅ ) modified CdS@Ni₃ S₂ heterojunction electrocatalysts. It is found that Ni₃ P modified CdS@Ni₃ S₂ (CdS@Ni₃ S₂ /Ni₃ P) exhibits remarkable stability and bifunctional electrocatalytic activities in both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Density functional theory results suggest that P-Ni sites and P sites in CdS@Ni₃ S₂ /Ni₃ P, respectively, serve as OER and HER active sites during electrocatalytic water splitting processes. Moreover, benefiting from the advantageous photocatalyst@electrocatalyst core@shell structure, CdS@Ni₃ S₂ /Ni₃ P delivers an advantaged photoassisted electrocatalytic water splitting property. The champion electrical to hydrogen and solar to hydrogen energy conversion efficiencies of CdS@Ni₃ S₂ /Ni₃ P, respectively, reach 93.35% and 4.65%. This work will provide a general guidance for synergistically using solar energy and electric energy for large-scale H₂ production from water splitting.

Unique Ni Crystalline Core/Ni Phosphide Amorphous Shell Heterostructured Electrocatalyst for Hydrazine Oxidation Reaction of Fuel Cells

It is highly attractive but challenging to develop transition-metal electrocatalysts for direct hydrazine fuel cells (DHzFCs). In this work, a nickel crystalline core@nickel phosphide amorphous shell heterostructured electrocatalyst supported by active carbon (Ni@NiP/C) is developed. Ni@NiP/C with a P/Ni molar ratio of 3:100, Ni@NiP_3.0/C, exhibits outstanding catalytic activity for the hydrazine oxidation reaction (HzOR) in alkaline solution, achieving a much better catalytic activity (2675.1 A g_Ni^-1@0.25 V vs RHE) and high stability, as compared to Ni nanoparticles supported on carbon (Ni/C) and Pt/C catalysts. The results indicate that formation of the NiP amorphous shell effectively inhibits the passivation of the Ni core active sites and enhances the adsorption of hydrazine on Ni by improving the adsorption energy, leading to high electrochemical activity and stability of the Ni@NiP_3.0/C catalysts for HzOR. The density functional theory calculation confirms the structural and electrocatalytic effect of the core-shell heterostructure on the stability and activity of Ni active sites for HzOR. The unique crystalline core/amorphous shell-structured Ni@NiP/C demonstrates promising potential as an effective electrocatalyst for DHzFCs.

Study of oxygen evolution reaction on amorphous Au13@Ni120P50 nanocluster

The pursuit of catalysts to promote effective water oxidization to produce oxygen has become a research subject of high priority for water splitting. Here, first-principles calculations are employed to study the water-splitting oxygen evolution reaction (OER) on ∼1.5 nm diameter Au13@Ni120P50 core-shell nanoclusters. Water splitting to produce oxygen proceeds in four intermediate reaction steps (OH*, O*, OOH* and O2). Adsorption configurations and adsorption energies for the species involved in OER on both Au13@Ni120P50 cluster and Ni12P5(001) supported by Au are presented. In addition, thermodynamic free energy diagrams and kinetic potential energy changes are systematically discussed. We show that the third intermediate reaction (O* reacting with H2O to produce OOH*) of the four elementary steps is the reaction-determining step, which accords with previous results. Also, the catalytic performance of OER for Au13@Ni120P50 is better than that for Ni12P5(001) supported by Au in terms of reactive overpotential (0.74 vs. 1.58 V) and kinetic energy barrier (2.18 vs. 3.17 eV). The optimal kinetic pathway for OER is further explored carefully for the Au13@Ni120P50 cluster. The low thermodynamic overpotential and kinetic energy barrier make Au13@Ni120P50 promising for industrial applications as a good OER electrocatalyst candidate.

Markedly enhanced visible-light photocatalytic H2 generation over g-C3N4 nanosheets decorated by robust nickel phosphide (Ni12P5) cocatalysts

Ni₁₂P₅ modified g-C₃N₄ photocatalysts exhibit significantly enhanced photocatalytic H₂-evolution activities under visible light irradiation.

A comprehensive investigation on adsorption of Ca (II), Cr (III) and Mg (II) ions by 3D porous nickel films

The present study reports the removal of Ca (II), Cr (III), Mg (II) ions from aqueous solution using 3D-porous nickel films (3DNFs) as a novel adsorbent material prepared by hydrogen bubble dynamic template (HBDT) method at room temperature. The structure morphology and the phase constitution of 3DNFs were characterized by FESEM, EDS and XRD. Adsorption process of Ca (II), Cr (III), Mg (II) ions was fast as the equilibrium was established within 30min, and the maximum adsorption at equilibrium was 44.1mg/g, 46.4mg/g and 32.7mg/g, respectively. The adsorption kinetics well fitted using a pseudo second-order kinetic model. The adsorption isotherm data of all the three metals fit well the Langmuir and Freundlich adsorption isotherm model. It was found out that kinetics of adsorption varies with initial concentration of metal ions. Thermodynamic parameters (i.e., the standard Gibbs free energies (ΔG), enthalpy change (ΔH), standard entropy change (ΔS)) were also evaluated. Thermodynamic analysis indicated that a high temperature is favored for the adsorption of metal ions by 3DNFs. These results suggest that 3DNFs have good potential application in effective adsorption of metal ions with satisfactory results.

Grass-like Co2P superstructures: direct synthesis between elements, forming mechanism and catalytic properties

Grass-like Co₂P superstructures with good catalytic performances were successfully prepared through a direct reaction between elements route.

Synthesis and characterization of MCM-49/MCM-41 composite molecular sieve: an effective adsorbent for chromate from water

MCM-49/MCM-41 was synthesized by a fast method via microwave assistance and was characterized for its application in heavy metal adsorption.

An efficient method for the synthesis of nickel phosphide nanocrystals via thermal decomposition of single-source precursors

We report an efficient method for the synthesis of nickel phosphide NCs for the first time. The size of Ni₂P NCs can be controlled by changing reaction temperature and OAm quantity. The phase of nickel phosphide NCs can be controlled by increasing reaction time.

Simple hydrothermal synthesis and photocatalytic performance of coral-like BaTiO3 nanostructures

Coral-like BaTiO₃ nanostructures with good photocatalytic performances were successfully prepared through a simple hydrothermal route.

Porous Ni/β-Ni(OH)2 superstructures: rapid solvothermal synthesis, characterization, and electrochemical property

The porous Ni/β-Ni(OH)2 superstructures have been successfully prepared via a simple, fast one-pot solvothermal route in the presence of cetyltrimethyl ammonium bromide (CTAB), using NiCl2·6H2O and NaBH4 as the original reactants. The reaction was carried out in ethylene glycol at 170°C for 1h. The morphology of the obtained product could be controlled by adjusting the reaction time and the surfactant. The products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), Infrared (IR) spectrometry, and Brunauer-Emmett-Teller (BET). The electrochemical property of the as-obtained superstructures was investigated through the cyclic voltammogram (CV) measurements. It was found that the as-obtained porous Ni/β-Ni(OH)2 superstructures exhibited good electrochemical properties and could be used as electrochemical sensors for the detection of some organic small molecules such as hydrochinone, pyrocatechol, and glucose.