d-Band Center Engineering of Nickel Nanoparticles Accelerates Water Dissociation for Hydrogen Evolution in Neutral NaCl Solution

While Pt is highly efficient for hydrogen evolution reaction (HER), its widespread use is limited by scarcity and high cost. Herein, a vertically aligned electrocatalyst is present comprising Ni3S2 nanotube arrays (NTAs) and Ni nanoparticles (NPs) (Ni3S2/Ni NTAs) for neutral HER. In a neutral 4 wt.% NaCl solution (pH = 7), the Ni3S2/Ni NTAs achieves a current density of 100 mA cm-2 at a low overpotential of 540 mV, outperforming both Ni3S2 NTAs and Ni NTAs and even the commercial Pt plate. The hollow tubular structure offers ample mass transfer channels, and strong electronic interaction between Ni3S2 and Ni is observed. Theoretical studies reveal that the lowered d-band center (ɛd) of Ni 3d orbital significantly reduces the activation energy for H2O dissociation and facilitates the movement of an H atom in H2O away from OH to form a transition state, consequently promoting H2 evolution. When Ni3S2/Ni NTAs is used as the cathode in a two-electrode diaphragm-free electrolyzer with a RuSnTi anode, efficient H2 production and energy-saving Cl2 evolution are achieved. This work highlights the potential of uniquely structured electrocatalysts for HER in neutral NaCl solutions.

Chitosan-Grafted Carbon Oxynitride Nanoparticles: Investigation of Photocatalytic Degradation and Antibacterial Activity

In this work, a series of chitosan (CS)-grafted carbon oxynitride (OCN) nanoparticles (denoted as CS-OCN) were successfully synthesized for the first time by thermal polycondensation and subsequent esterification. The structure and photocatalytic performance of CS-OCN nanoparticles were investigated. The XPS spectra of CS-OCN-3 showed the presence of amino bonds. The optimal photocatalytic degradation efficiency of the synthesized CS-OCN-3 could reach 94.3% within 390 min, while the photocurrent response intensity was about 150% more than that of pure OCN. The improved photocatalytic performance may be mainly attributed to the enhanced photogenerated carrier's separation and transportation and stronger visible light response after CS grafting. In addition, the inhibition diameter of CS-OCN-3 reached 23 mm against E. coli within 24 h under visible light irradiation, exhibiting excellent photocatalytic bactericidal ability. The results of bacterial inhibition were supported by absorbance measurements (OD600) studies of E. coli. In a word, this work provided a rational design of an efficient novel metal-free photocatalyst to remove bacterial contamination and accelerate the degradation of organic dyes.

Magnetic, Electronic, and Optical Studies of Gd-Doped WO3: A First Principle Study

Tungsten trioxide (WO₃) is mainly studied as an electrochromic material and received attention due to N-type oxide-based semiconductors. The magnetic, structural, and optical behavior of pristine WO₃ and gadolinium (Gd)-doped WO₃ are being investigated using density functional theory. For exchange-correlation potential energy, generalized gradient approximation (GGA+U) is used in our calculations, where U is the Hubbard potential. The estimated bandgap of pure WO₃ is 2.5 eV. After the doping of Gd, some states cross the Fermi level, and WO₃ acts as a degenerate semiconductor with a 2 eV bandgap. Spin-polarized calculations show that the system is antiferromagnetic in its ground state. The WO₃ material is a semiconductor, as there is a bandgap of 2.5 eV between the valence and conduction bands. The Gd-doped WO₃’s band structure shows few states across the Fermi level, which means that the material is metal or semimetal. After the doping of Gd, WO₃ becomes the degenerate semiconductor with a bandgap of 2 eV. The energy difference between ferromagnetic (FM) and antiferromagnetic (AFM) configurations is negative, so the Gd-doped WO₃ system is AFM. The pure WO₃ is nonmagnetic, where the magnetic moment in the system after doping Gd is 9.5599575 μB.

Emerging S-Scheme Photocatalyst

Photocatalysis is a green technology to use ubiquitous and intermittent sunlight. The emerging S-scheme heterojunction has demonstrated its superiority in photocatalysis. This article covers the state-of-the-art progress and provides new insights into its general designing criteria. It starts with the challenges confronted by single photocatalyst from the perspective of energy dissipation by borrowing the common behaviors in the dye molecule. Subsequently, other problems faced by single photocatalyst are summarized. Then a viable solution for these problems is the construction of heterojunctions. To overcome the problems and mistakes of type-II and Z-scheme heterojunctions, S-scheme heterojunction is proposed and the underlying reaction mechanism is summarized. Afterward, the design principles for S-scheme heterojunction are proposed and four types of S-scheme heterojunctions are suggested. Following this, direct characterization techniques for testifying the charge transfer in S-scheme heterojunction are presented. Finally, different photocatalytic applications of S-scheme heterojunctions are summarized. Specifically, this work endeavors to clarify the critical understanding on curved Fermi level in S-scheme heterojunction interface, which can help strengthen and advance the fundamental theories of photocatalysis. Moreover, the current challenges and prospects of the S-scheme heterojunction photocatalyst are critically discussed.

Hot injection-induced synthesis of ZnCdS-rGO/MoS2 heterostructures for efficient hydrogen production and CO2 photoreduction

A highly efficient hybrid ZnCdS-rGO/MoS₂ heterostructure is successfully synthesized through a hot injection method and control loading of rGO/MoS₂. The synergism provides an unprecedently high H₂-generation rate of 193.4 mmol H₂ g^-1 h^-1 from water under full arc solar radiation and MeOH production (5.26 mmol g^-1 h^-1, AQY of 14.6% at λ = 420 ± 20 nm) from CO₂ reduction.

Efficient hydrogen production at a rationally designed MoSe2@Co3O4 p-n heterojunction

During the past several years, transition metal compounds have shown high activity in the field of photocatalysis. Therefore, the MoSe₂@Co₃O₄ with excellent photocatalytic properties through simple hydrothermal and physical mixing methods was prepared. This composite material was composed of n-type semiconductor MoSe₂ and p-type semiconductor Co₃O₄. After optimizing the loading of Co₃O₄, the optimal hydrogen production can reached 7029.2 μmol g^-1h^-1, which was 2.34 times that of single MoSe₂. In addition, some characterization methods were used to explore the hydrogen production performance of the composite catalyst under EY sensitized conditions. Among them, the UV-vis diffuse reflectance spectra suggests that MoSe₂@Co₃O₄ exhibits stronger visible light absorption performance than the single material. Fluorescence performance and photoelectrochemical characterization experiments further prove that, the special structure formed by MoSe₂ and Co₃O₄ and the existence of p-n heterojunction effectively accelerate the separation and transfer of carriers meanwhile inhibit the recombination probability of electron-hole pairs. Combined with other characterizations such as XRD, XPS, SEM and BET, the possible hydrogen production mechanism was proposed.

Recent Progress of Transition Metal Phosphides for Photocatalytic Hydrogen Evolution

Photocatalytic hydrogen evolution can effectively alleviate the troublesome global energy crisis by converting solar energy into the chemical energy of hydrogen. In order to realize efficient hydrogen generation, a variety of semiconductor materials have been extensively investigated, including TiO₂ , CdS, g-C₃ N₄ , metal-organic frameworks (MOFs), and others. In recent years, to achieve higher photocatalytic performance and reach the level of large-scale industrial applications, photocatalysts decorated with transition metal phosphides (TMPs) have shone brightly because of their low cost, stable physical and chemical properties, and substitution for precious metals of TMPs. This Review highlights the preparation methods and properties associated with photocatalysis of TMPs. Moreover, the H₂ generation efficiency of photocatalysts loaded with TMPs and the roles of TMPs in catalytic systems are also studied systematically. Apart from being co-catalysts, several TMPs can also serve as host catalysts to boost the activity of photocatalytic composites. Finally, the development prospects and challenges of TMPs are put forward, which is valuable for future researchers to expand the application of TMPs in photocatalytic directions and to develop more active photocatalytic systems.

Ni-MOF-74 derived nickel phosphide and In2O3 form S-scheme heterojunction for efficient hydrogen evolution

The composite structure of Ni2P/In2O3 constructs an S-scheme heterojunction that transfers useless electrons and holes to the composite interface for consumption.The loading of In2O3 further increases the photocatalytic hydrogen production activity.

A sea-urchin-structured NiCo2O4 decorated Mn0.05Cd0.95S p–n heterojunction for enhanced photocatalytic hydrogen evolution

The development of low-cost and high-efficiency photocatalysts is an important way to realize photocatalytic hydrogen production.

An amorphous nickel boride-modified ZnxCd1−xS solid solution for enhanced photocatalytic hydrogen evolution

In this work, the rational design of amorphous Ni_xB as a co-catalyst for the modification of Zn_xCd_1−xS was achieved.