Nanoporous cobalt-doped AlNi3/NiO architecture for high performing hydrogen evolution at high current densities

Engineering platinum-free catalysts for hydrogen evolution reaction (HER) with high activity and stability is essential for electrochemical hydrogen production. In this paper, we report the synthesis of cobalt-doped AlNi3/NiO (Co-AlNi3/NiO) electrode with three-dimensional nanoporous structure via chemical dealloying method. Density functional theory (DFT) calculations reveal that Co-AlNi3/NiO can accelerate water adsorption / dissociation and optimize adsorption-desorption energies of H* intermediates, thus improving the intrinsic HER activity. Both the introduction of Co and Al can efficiently ameliorate the electronic density around Ni sites of NiO and AlNi3, which can effectively reduce the energy barrier towards Volmer-Heyrovsky reaction and thus synergistically promote the hydrogen evolution. Benefiting from the large electrochemical active surface area, high electrical conductivity and electronic effect, the nanoporous Co-AlNi3/NiO catalyst exhibits remarkable HER activity with an overpotential of 73 mV at a current density of 10 mA cm-2 in alkaline condition, outperforming most of the reported non-precious metal catalysts. The nanoporous Co-AlNi3/NiO catalyst can operate continuously over 1000 h at high current densities with a robust stability. This work provides a new vision for the development of low-cost and efficient electrocatalysts for energy conversion applications.

In-situ fabrication of self-supported cobalt molybdenum sulphide on carbon paper for bifunctional water electrocatalysis

The fabrication of highly efficient yet stable noble-metal-free bifunctional electrocatalysts that can simultaneously catalyse both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) remains challenging. Herein, we employ the heterostructure coupling strategy, showcasing an aerosol-assisted chemical vapour deposition (AACVD) aided synthetic approach for the in-situ growth of cobalt molybdenum sulphide nanocomposites on carbon paper (CoMoS@CP) as a bifunctional electrocatalyst. The AACVD allows the rational incorporation of Co in the Mo-S binary structure, which modulates the morphology of CoMoS@CP, resulting in enhanced HER activity (ŋ10 = 171 mV in acidic and ŋ10 = 177 mV in alkaline conditions). Furthermore, the CoS2 species in the CoMoS@CP ternary structure extends the OER capability, yielding an ŋ100 of 455 mV in 1 M KOH. Lastly, we found that the synergistic effect of the Co-Mo-S interface elevates the bifunctional performance beyond binary counterparts, achieving a low cell voltage (1.70 V at 10 mA cm-2) in overall water splitting test and outstanding catalytic stability (∼90 % performance retention after 50-/30-h continuous operation at 10 and 100 mA cm-2, respectively). This work has opened up a new methodology for the controllable synthesis of self-supported transition metal-based electrocatalysts for applications in overall water splitting.

CoS2-decorated CdS nanorods for efficient degradation of organic pollutants

The heterostructure between CoS2 and CdS can improve the charge separation efficiency during photocatalysis and promote the generation of more OH and O2− radicals under light irradiation.

Construction of CoS2 /Zn0.5 Cd0.5 S S-Scheme Heterojunction for Enhancing H2 Evolution Activity Under Visible Light

In the field of photocatalysis, building a heterojunction is an effective way to promote electron transfer and enhance the reducibility of electrons. Herein, the S-scheme heterojunction photocatalyst (CoS₂ /Zn_0.5 Cd_0.5 S) of CoS₂ nanospheres modified Zn_0.5 Cd_0.5 S solid solution was synthesized and studied. The H₂ evolution rate of the composite catalyst reached 25.15 mmol g^-1  h^-1 , which was 3.26 times that of single Zn_0.5 Cd_0.5 S, whereas pure CoS₂ showed almost no hydrogen production activity. Moreover, CoS₂ /Zn_0.5 Cd_0.5 S had excellent stability and the hydrogen production rate after six cycles of experiments only dropped by 6.19 %. In addition, photoluminescence spectroscopy and photoelectrochemical experiments had effectively proved that the photogenerated carrier transfer rate of CoS₂ /Zn_0.5 Cd_0.5 S was better than CoS₂ or Zn_0.5 Cd_0.5 S single catalyst. In this study, the synthesized CoS₂ and Zn_0.5 Cd_0.5 S were both n-type semiconductors. After close contact, they followed an S-scheme heterojunction electron transfer mechanism, which not only promoted the separation of their respective holes and electrons, but also retained a stronger reduction potential, thus promoting the reduction of H⁺ protons in photocatalytic experiments. In short, this work provided a new basis for the construction of S-scheme heterojunction in addition to being used for photocatalytic hydrogen production.

Transition metal sulfides meet electrospinning: versatile synthesis, distinct properties and prospective applications

One-dimensional (1D) electrospun nanomaterials have attracted significant attention due to their unique structures and outstanding chemical and physical properties such as large specific surface area, distinct electronic and mass transport, and mechanical flexibility. Over the past years, the integration of metal sulfides with electrospun nanomaterials has emerged as an exciting research topic owing to the synergistic effects between the two components, leading to novel and interesting properties in energy, optics and catalysis research fields for example. In this review, we focus on the recent development of the preparation of electrospun nanomaterials integrated with functional metal sulfides with distinct nanostructures. These functional materials have been prepared via two efficient strategies, namely direct electrospinning and post-synthesis modification of electrospun nanomaterials. In this review, we systematically present the chemical and physical properties of the electrospun nanomaterials integrated with metal sulfides and their application in electronic and optoelectronic devices, sensing, catalysis, energy conversion and storage, thermal shielding, adsorption and separation, and biomedical technology. Additionally, challenges and further research opportunities in the preparation and application of these novel functional materials are also discussed.

Synthesis of Lattice-Contracted Cobalt Disulfide as an Outstanding Oxygen Reduction Reaction Catalyst via Self-assembly Arrangement

Identifying high-performance non-precious metal-based catalysts at the cathode is a major challenge for future practical applications. Herein, a soft-template route through a self-assembly arrangement of sulfur sources was successfully developed, facilitating the anion exchange. In addition, compared with pristine cobalt disulfide synthesized without templates, the cobalt disulfide prepared using the new method presented a lattice shrinking phenomenon due to the hindrance of cobalt hydroxide crystal cell. Based on X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculation, increased occupancy of e_g orbitals was verified for the cobalt disulfide after shrinkage, which was the main factor for enhancing the intrinsic activity of the catalyst. Besides the microscopic morphologic structure, elementary composition, and the valence state of the elements, the possible growth process of the cobalt disulfide was also discussed in detail. As catalyst for the oxygen reduction reaction, CoS₂ showed a similar half-wave potential (0.81 vs. 0.84 V for Pt/C) and higher diffusion-limiting current density (reaching 5.33 vs. 5.19 mA cm^-2 for Pt/C) than a commercial Pt/C catalyst. Hence, our results provide a rational design direction for this type of catalysts.

Cobalt disulfide supported on porous carbon foam as a high performance hydrogen evolution reaction catalyst

An excellent cobalt disulfide–carbon foam composite catalyst was synthesized by a hydrothermal method for the electrochemical hydrogen evolution reaction (HER).

Self-Supported Vanadium Carbide by an Electropolymerization-Assisted Method for Efficient Hydrogen Production

Exploring efficient electrodes toward the hydrogen evolution reaction (HER) remains a great challenge for large-scale hydrogen production. Owing to its high earth abundance, low electrical resistivity, and small density, vanadium carbide (VC) is a promising HER electrode candidate but has been rarely explored. In this work, VC nanoparticles encased in nitrogen-doped carbon matrix on carbon cloth (VC@NC/CC) were prepared as a binder-free HER cathode through electropolymerization followed by carbothermal reduction under argon. In the first step of pyrrole electropolymerization, the VO₄ ^3- anions, serving as both vanadium source and supporting electrolyte, were homogeneously incorporated in the positively charged polypyrrole (PPy) framework through coulombic interaction. The electropolymerization was effective for preparation of binder-free metal carbide materials with various polymer monomers as carbon source, which was favorable for the high performance of metal carbide electrodes. During the pyrolysis process, the polymeric hybrids were converted to VC nanoparticles and entrapped in the PPy-derived N-doped carbon matrix. The optimized VC@NC/CC electrode exhibited high catalytic activity and durability in both acidic and alkaline media. The use of VC for efficient HER is remarkable, and such a convenient and versatile electropolymerization-assisted method is appealing for the fabrication of industrially scalable large-area VC electrodes for efficient hydrogen production.

Improving catalysis for electrochemical water splitting using a phosphosulphide surface

A yolk–shell-structured porous phosphosulphide catalyst exhibits superior activities towards the hydrogen and oxygen evolution reactions in water splitting in an alkaline electrolyte.

HFIP-Functionalized Co3 O4 Micro-Nano-Octahedra/rGO as a Double-Layer Sensing Material for Chemical Warfare Agents

Semiconductor metal oxides (SMO)-based gas-sensing materials suffer from insufficient detection of a specific target gas. Reliable selectivity, high sensitivity, and rapid response-recovery times under various working conditions are the main requirements for optimal gas sensors. Chemical warfare agents (CWA) such as sarin are fatal inhibitors of acetylcholinesterase in the nerve system. So, sensing materials with high sensitivity and selectivity toward CWA are urgently needed. Herein, micro-nano octahedral Co₃ O₄ functionalized with hexafluoroisopropanol (HFIP) were deposited on a layer of reduced graphene oxide (rGO) as a double-layer sensing materials. The Co₃ O₄ micro-nano octahedra were synthesized by direct growth from electrospun fiber templates calcined in ambient air. The double-layer rGO/Co₃ O₄ -HFIP sensing materials presented high selectivity toward DMMP (sarin agent simulant, dimethyl methyl phosphonate) versus rGO/Co₃ O₄ and Co₃ O₄ sensors after the exposure to various gases owing to hydrogen bonding between the DMMP molecules and Co₃ O₄ -HFIP. The rGO/Co₃ O₄ -HFIP sensors showed high stability with a response signal around 11.8 toward 0.5 ppm DMMP at 125 °C, and more than 75 % of the initial response was maintained under a saturated humid environment (85 % relative humidity). These results prove that these double-layer inorganic-organic composite sensing materials are excellent candidates to serve as optimal gas-sensing materials.

Advanced electrospun nanomaterials for highly efficient electrocatalysis

We highlight the recent developments of electrospun nanomaterials with controlled morphology, composition and architecture for highly efficient electrocatalysis.

Co9S8@MoS2 Core-Shell Heterostructures as Trifunctional Electrocatalysts for Overall Water Splitting and Zn-Air Batteries

The development of efficient non-noble-metal electrocatalysts is of critical importance for clean energy conversion systems, such as fuel cells, metal-air batteries, and water electrolysis. Herein, uniform Co₉S₈@MoS₂ core-shell heterostructures have been successfully prepared via a solvothermal approach, followed by an annealing treatment. Transmission electron microscopy, X-ray absorption near-edge structure, and X-ray photoelectron spectroscopy measurements reveal that the core-shell structure of Co₉S₈@MoS₂ can introduce heterogeneous nanointerface between Co₉S₈ and MoS₂, which can deeply influence its charge state to boost the electrocatalytic performances. Besides, due to the core-shell structure that can promote the synergistic effect of Co₉S₈ and MoS₂ and provide abundant catalytically active sites, Co₉S₈@MoS₂ exhibits a superior hydrogen evolution reaction performance with a small overpotential of 143 mV at 10 mA cm^-2 and a small Tafel slope value of 117 mV dec^-1 under alkaline solution. Meanwhile, the activity of Co₉S₈@MoS₂ toward oxygen evolution reaction is also impressive with a low operating potential (∼1.57 V vs reversible hydrogen electrode) at 10 mA cm^-2. By using Co₉S₈@MoS₂ catalyst for full water splitting, an alkaline electrolyzer affords a cell voltage as low as 1.67 V at a current density of 10 mA cm^-2. Also, Co₉S₈@MoS₂ reveals robust oxygen reduction reaction performance, making it an excellent catalyst for Zn-air batteries with a long lifetime (20 h). This work provides a new means for the development of multifunctional electrocatalysts of non-noble metals for the highly demanded electrochemical energy technologies.

Effects of graphitization of carbon nanospheres on hydrodeoxygenation activity of molybdenum carbide

The hydrodeoxygenation catalytic activity and stability of carbon supported molybdenum carbide catalysts could be improved by graphitizing their carbon supports.

Engineering Pt/Pd Interfacial Electronic Structures for Highly Efficient Hydrogen Evolution and Alcohol Oxidation

Tailoring the interfacial structure of Pt-based catalysts has emerged as an effective strategy to improve catalytic activity. However, little attention has been focused on investigating the relationship between the interfacial facets and their catalytic activity. Here, we design and implement Pd-Pt interfaces with controlled heterostructure features by epitaxially growing Pt nanoparticles on Pd nanosheets. On the basis of both density functional theory calculation and experimental results, we demonstrate that charge transfer from Pd to Pt is highly dependent on the interfacial facets of Pd substrates. Therefore, the Pd-Pt heterostructure with Pd(100)-Pt interface exhibits excellent activity and long-term stability for hydrogen evolution and methanol/ethanol oxidation reactions in alkaline medium, much better than that with Pd (111)-Pt interface or commercial Pt/C. Interfacial crystal facet-dependent electronic structural modulation sheds a light on the design and investigation of new heterostructures for high-activity catalysts.

Ultrafine Co-based Nanoparticle@Mesoporous Carbon Nanospheres toward High-Performance Supercapacitors

A general synthetic methodology is reported to grow ultrafine cobalt-based nanoparticles (NPs, 2-7 nm) within high-surface-area mesoporous carbon (MC) frameworks. Our design strategy is based on colloidal amphiphile (CAM) templated oxidative self-polymerization of dopamine. The CAM templates consisting of a hydrophobic silica-like core and a hydrophilic PEO shell can coassemble with dopamine and template its self-polymerization to form polydopamine (PDA) nanospheres. Given that PDA has rich binding sites such as catechol and amine to coordinate metal ions (e.g., Co²⁺), PDA nanospheres containing Co²⁺ ions can be converted into hierarchical porous carbon frameworks containing ultrafine metallic Co NPs (Co@MC) using high-temperature pyrolysis. The CAM templates offer strong "nanoconfinements" to prevent the overgrowth of Co NPs within carbon frameworks. The yielded ultrafine Co NPs have an average size of <7 nm even at a very high loading of 65 wt %. Co@MC can be further converted into various oxides and sulfides, e.g., CoO, Co₃O₄, CoS₂ and transition-metal doped bimetallic Co_xM_1-xS₂, without significantly changing the size of NPs. As a proof-of-concept application, the porous Co-based NPs@MC hybrids were used as electrode materials for supercapacitors, which exhibit excellent supercapacitive performance with outstanding long-term cycling stability, due to the features such as ultrafine size, controllable chemical compositions, hierarchical porous structures, and full coverage of conductive carbons.

Electrospun carbon nanofiber@CoS2 core/sheath hybrid as an efficient all-pH hydrogen evolution electrocatalyst

CNF@CoS₂ hybrids with a core/sheath hierarchical structure have been successfully fabricated for use as efficient all-pH HER electrocatalysts.