Triple-Shelled Co-VSex Hollow Nanocages as Superior Bifunctional Electrode Materials for Efficient Pt-Free Dye-Sensitized Solar Cells and Hydrogen Evolution Reactions

Constructing a Functionalized Electrocatalyst of a Transition Metal Chalcogenide on Accordion-Like MXene to Boost the Hydrogen Evolution Reaction

MXenes exhibit unique layered structures and excellent electrical conductivity, and their multiple surface termination groups are favorable for hosting impressive performance for electrochemical reactions. Therefore, a two-dimensional (2D) layered MXene-based catalyst may become a novel high-efficiency electrocatalyst to replace traditional noble metal electrocatalysts. In this work, a transition metal chalcogenide (MoS2/CuS) and MXene are combined to prepare a 2D electrocatalyst (MoS2/CuS/MXene) for the hydrogen evolution reaction (HER). MXene exhibited a large specific surface area in the shape of an accordion, which was very beneficial for the growth of nanomaterials. CuS/MXene promoted electron transfer and improved the exposed active site for HER. The exposed MoS2 edges exhibited a high chemical adsorption capacity, which is conducive to HER. Electrochemical tests reveal that the MoS2/CuS/MXene electrocatalyst can reduce the charge transfer resistance toward the HER and increase active sites for HER, leading to enhancing the catalytic performance. The MoS2/CuS/MXene electrocatalyst affords an efficient HER with a low overpotential (115 mV@10 mA cm-2). This work offers a new idea to create layered transition metal chalcogenide- and MXene-based electrocatalysts for HER.

Development of polyoxometalate-based Ag-H2biim inorganic-organic hybrid compounds functionalized for the acid electrocatalytic hydrogen evolution reaction

The electrocatalytic hydrogen evolution reaction (HER) is an ideal method for hydrogen production. Transition metal complex electrocatalysts exhibit poor HER activity due to excessive or weak adsorption of H during the electrochemical reduction of water to molecular hydrogen in acidic environments. Developing specific functional complex materials as desired catalysts is challenging. Here, an electrochemical surface restructuring strategy of polyoxometalate (POM)-modified Ag materials toward the HER with a dramatically decreased overpotential under acidic aqueous conditions is established. We prepared two POM [SiW12O40]4- (SiW12)/[P2W18O62]6- (P2W18)-based Ag-2,2'-biimidazole (H2biim) inorganic-organic hybrid compounds (1 and 2) via the hydrothermal method and these two compounds undergo an electrochemical restructuring process in 0.5 M H2SO4 during the HER, in which Ag nanoparticles are in situ formed with the basic structures of SiW12 and P2W18 being maintained. The activated catalysts (1-AC-RDE and 2-AC-RDE) exhibit good electrocatalytic activity for the HER with good long-term stability, and the required overpotentials at a current density of 10 mA cm-2 are 112 mV (1-AC-RDE) and 91 mV (2-AC-RDE) with Tafel slopes of 77 mV dec-1 and 65 mV dec-1, respectively. The excellent electron-proton storage and transferability of SiW12 and P2W18 may provide a solution for the insufficient capture of H by Ag, leading to an effective self-optimizing behavior and superior acidic HER activity.

Pt-Doped Biomass Carbon Decorated with MoS2 Nanosheets as an Electrocatalyst for Hydrogen Evolution

It is necessary to develop an efficient hydrogen evolution catalyst to improve the efficiency of the hydrogen evolution reaction (HER). Herein, a MoS₂ nanosheet is decorated on the Pt-doping biomass yeast cells (MoS₂@Pt/YC) via a simple hydrothermal process. Reducing the noble metal loading without compromising its performance is a challenging task. The smooth surface of YCs is conducive to the growth of MoS₂ nanosheets, and its functional groups provide attachment sites for metal Pt. The Pt/YC is covered with MoS₂ nanosheets, thus improving the exposed active sites for HER. The obtained MoS₂@Pt/YC delivers a competitive overpotential of 118 mV at the benchmark current density of 10 mA cm^-2 and achieves a small Tafel slope of 74 mV dec^-1, indicating the great HER performance of MoS₂@Pt/YC. Moreover, MoS₂@Pt/YC shows robust stability after 24 h of continuous operation toward HER in acidic solution. By introducing transition metal sulfides with high specific surface area, the loading of precious metals can be reduced without compromising properties. This work provides a method to design Pt-doping HER electrocatalysts through a simple method. The facile preparation process for MoS₂@Pt/YC and its outstanding performance allow it to be a promising electrocatalyst for practical HER application.

ZIF-67-Derived (NiCo)S2@NC Nanosheet Arrays Hybrid for Efficient Overall Water Splitting

Electrocatalytic water splitting is considered a promising approach to obtain clean and sustainable hydrogen energy. The integration of optimal nanoarchitecture and multicomponent synergy has been a significant factor for designing a bifunctional electrocatalyst to promote the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). In particular, the charge migration, mass transfer, and gas release rate in the catalyzing process are closely correlated with the architecture of the catalyst. Here, ZIF-67-derived N-doped carbon nanofiber-supported (NiCo)S₂ nanosheet [(NiCo)S₂/NCNF] as a bifunctional electrocatalyst was synthesized using electrospinning, template etching, and subsequent gas sulfidation method. The hierarchical hybrid nanofiber with inner hollow cubes and outer nanosheets provides easy electron penetration, high charge/mass transportation efficiency, and robust structure stability. Furthermore, the MOF-derived carbon-encapsuled bimetal-sulfide and the synergistic effect of double active centers are conducive to an exceptional performance, showing low overpotentials of 177 and 203 mV to drive a current density of 10 mA cm^-2 and robust stability for the HER and OER, respectively. Meanwhile, the (NiCo)S₂/NCNF electrodes exhibit a small voltage of 1.61 V for overall water splitting activity with an electrolyzer cell at current densities of 10 mA cm^-2 over 12 h. This work presents novel insights into the bifunctional catalyst for promoting the overall water splitting via a MOF-derived nanoarchitecture and multicomponent synergy.

Critical Review, Recent Updates on Zeolitic Imidazolate Framework-67 (ZIF-67) and Its Derivatives for Electrochemical Water Splitting

Design and construction of low-cost electrocatalysts with high catalytic activity and long-term stability is a challenging task in the field of catalysis. Metal-organic frameworks (MOF) are promising candidates as precursor materials in the development of highly efficient electrocatalysts for energy conversion and storage applications. This review starts with a summary of basic concepts and key evaluation parameters involved in the electrochemical water-splitting reaction. Then, different synthesis approaches reported for the cobalt-based Zeolitic imidazolate framework (ZIF-67) and its derivatives are critically reviewed. Additionally, several strategies employed to enhance the electrocatalytic activity and stability of ZIF-67-based electrocatalysts are discussed in detail. The present review provides a succinct insight into the ZIF-67 and its derivatives (oxides, hydroxides, sulfides, selenides, phosphide, nitrides, telluride, heteroatom/metal-doped carbon, noble metal-supported ZIF-67 derivatives) reported for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water splitting applications. Finally, this review concludes with the associated challenges and the perspectives on developing the best economic, durable electrocatalytic materials.

Strategic Design of a Bifunctional NiFeCoW@NC Hybrid to Replace the Noble Platinum for Dye-Sensitized Solar Cells and Hydrogen Evolution Reactions

High-performance triiodide reduction reaction (IRR) catalysts in dye-sensitized solar cells (DSSCs) and hydrogen evolution reaction (HER) catalysts in electrochemical water splitting are extremely compelling for renewable energy conversion and storage. The best IRR and HER catalysts generally rely on the use of noble metal platinum (Pt), which suffers obstacles in real-world implementation. The rational design of efficient bifunctional IRR and HER catalysts based on inexpensive and earth-abundant elements to replace scarce Pt could enable low-cost photoelectric conversion and hydrogen production but is challenging and rarely reported. Herein, we present a bifunctional NiFeCoW@NC hybrid with the unique architecture of WC loaded on the in situ formed carbon nanotubes embedded with Co-doped FeNi₃ nanoparticles based on the anisotropic integration design principle, which operates efficiently for DSSCs and hydrogen evolution. The assembled DSSCs using the designed multimetal-based NiFeCoW@NC counter electrode delivered a high power conversion efficiency of 6.92% and long-term stability superior to bimetal-based NiFe@NC, CoW@NC, and Pt counterparts. It also exhibited eminent hydrogen evolution performance with a low overpotential of 127.8 mV to drive a 10 mA cm^-2 current density, a Tafel slope of 60.4 mV dec^-1, and satisfactory durable stability in 0.5 M H₂SO₄. This work provides a design principle for low-cost and highly active bifunctional catalysts to replace Pt for DSSCs and hydrogen evolution.

A hierarchical structure of a Co0.85Se@NC/ZnSe@NC yolk-double-shell polyhedron for long-term lithium storage

Constructing nanostructures with multi-components and delicate architecture exhibits huge potential to improve the lithium storage performance of electrodes. Herein, we report a novel yolk-double-shell structure with complex chemical compositions. Starting with a core-shell structured Co-ZIF@ZnCo-ZIF as a precursor via a simple selenization process, yolk-double-shell polyhedra that assembled by nanosized Co_0.85Se@N-doped carbon as the yolk and the first shell and nanosized Co_0.85Se@N-doped carbon and ZnSe@N-doped carbon hetero-components as the second shell (marked as Co_0.85Se@NC/ZnSe@NC-YDS) are synthesized. Benefiting from their multiple structural advantages, such as high surface area, large pore volume, uniform carbon coating, and intimate heterostructures, Co_0.85Se@NC/ZnSe@NC-YDS exhibits high reversible capacity (1047 mA h g^-1) and good rate capability for lithium storage. More importantly, even after 3000 cycles at 5.0 A g^-1, an impressive reversible capacity of 468 mA h g^-1 is retained with no capacity decay. After repeated discharge/charge processes, the integrated yolk-double-shell structure is still reserved, due to its structural and compositional advantages, which contribute to the enhanced rate and cycling performance.

Selenic Acid Etching Assisted Vacancy Engineering for Designing Highly Active Electrocatalysts toward the Oxygen Evolution Reaction

Oxygen evolution electrocatalysts are central to overall water splitting, and they should meet the requirements of low cost, high activity, high conductivity, and stable performance. Herein, a general, selenic-acid-assisted etching strategy is designed from a metal-organic framework as a precursor to realize carbon-coated 3d metal selenides M_m Se_n (Co_0.85 Se_{1- x} , NiSe_{2- x} , FeSe_{2- x} ) with rich Se vacancies as high-performance precious metal-free oxygen evolution reaction (OER) electrocatalysts. Specifically, the as-prepared Co_0.85 Se_{1- x} @C nanocages deliver an overpotential of only 231 mV at a current density of 10 mA cm^-2 for the OER and the corresponding full water-splitting electrolyzer requires only a cell voltage of 1.49 V at 10 mA cm^-2 in alkaline media. Density functional theory calculation reveals the important role of abundant Se vacancies for improving the catalytic activity through improving the conductivity and reducing reaction barriers for the formation of intermediates. Although phase change after long-term operation is observed with the formation of metal hydroxides, catalytic activity is not obviously affected, which strengthens the important role of the carbon network in the operating stability. This study provides a new opportunity to realize high-performance OER electrocatalysts by a general strategy on selenic acid etching assisted vacancy engineering.

Surface Atom Regulation on Polyoxometalate Electrocatalyst for Simultaneous Low-Voltage H2 Production and Phenol Degradation

The electrocatalytic hydrogen evolution reaction is an ideal method for H₂ production. To improve the performance of polyoxometalate-based electrocatalyst in the hydrogen evolution reaction, one O^2- in polyoxometalate is replaced by S^2-. This weakens the binding of polyoxometalate to H*, facilitates its desorption, and improves the H₂ generation property. Vulcanized polyoxometalate only requires 55 mV to achieve 10 mA·cm^-2 current in the hydrogen evolution reaction. This electrocatalyst also exhibits promising performance in phenol degradation reaction, which is an ideal substitute for high-energy-consuming oxygen evolution reaction in H₂ production due to low voltage to drive. To acquire 100 and 200 mA·cm^-2 in the phenol degradation reaction, this vulcanized polyoxometalate only consumes 1.38 and 1.41 V. With this electrocatalyst working as a cathode and an anode simultaneously, an electrolyzer is constructed by employing phenol-containing KOH as an electrolyte. To obtain 100 and 200 mA·cm^-2 current, the electrolyzer only requires 1.54 and 1.57 V. Because energy-efficient phenol degradation reaction occurs, these values are obviously lower than the oxygen evolution reaction involved in the overall water-splitting H₂ production. This work provides a universal method to enhance the hydrogen evolution reaction (HER) activity of polyoxometalates. Furthermore, a new method is explored, which achieves energy conservation and phenol degradation simultaneously in H₂ production.

1D-CoSe2 nanoarray: a designed structure for efficient hydrogen evolution and symmetric supercapacitor characteristics

Direct growth of self-supported one-dimensional (1D) nanorod arrays on conducting substrates is highly attractive for electrocatalysis, due to their unique shape, size, and length.