Hierarchical MoSe2-CoSe2 nanotubes anchored on graphene nanosheets: A highly efficient and stable electrocatalyst for hydrogen evolution in alkaline medium

Mo-doping heterojunction: interfacial engineering in an efficient electrocatalyst for superior simulated seawater hydrogen evolution

Exploring economical, efficient, and stable electrocatalysts for the seawater hydrogen evolution reaction (HER) is highly desirable but is challenging. In this study, a Mo cation doped Ni0.85Se/MoSe2 heterostructural electrocatalyst, Mox-Ni0.85Se/MoSe2, was successfully prepared by simultaneously doping Mo cations into the Ni0.85Se lattice (Mox-Ni0.85Se) and growing atomic MoSe2 nanosheets epitaxially at the edge of the Mox-Ni0.85Se. Such an Mox-Ni0.85Se/MoSe2 catalyst requires only 110 mV to drive current densities of 10 mA cm-2 in alkaline simulated seawater, and shows almost no obvious degradation after 80 h at 20 mA cm-2. The experimental results, combined with the density functional theory calculations, reveal that the Mox-Ni0.85Se/MoSe2 heterostructure will generate an interfacial electric field to facilitate the electron transfer, thus reducing the water dissociation barrier. Significantly, the heteroatomic Mo-doping in the Ni0.85Se can regulate the local electronic configuration of the Mox-Ni0.85Se/MoSe2 heterostructure catalyst by altering the coordination environment and orbital hybridization, thereby weakening the bonding interaction between the Cl and Se/Mo. This synergistic effect for the Mox-Ni0.85Se/MoSe2 heterostructure will simultaneously enhance the catalytic activity and durability, without poisoning or corrosion of the chloride ions.

Metal selenide nanomaterials for biomedical applications

Metal selenide nanomaterials have received enormous attention as they possess diverse compositions, microstructures, and properties. The combination of selenium with various metallic elements gives the metal selenide nanomaterials distinctive optoelectronic and magnetic properties, such as strong near-infrared absorption, excellent imaging properties, good stability, and long in vivo circulation. This makes metal selenide nanomaterials advantageous and promising for biomedical applications. This paper summarizes the research progress in the last five years in the controlled synthesis of metal selenide nanomaterials in different dimensions and with different compositions and structures. Then we discuss how surface modification and functionalization strategies are well-suited for biomedical fields, including tumor therapy, biosensing, and antibacterial biological applications. The future trends and issues of metal selenide nanomaterials in the biomedical field are also discussed.

Construction of Cobalt Molybdenum Diselenide Three-phase Heterojunctions for Electrocatalytic Hydrogen Evolution in Acid Medium

Molybdenum diselenide and cobalt diselenide have been commonly implemented in electrocatalytic hydrogen evolution reaction (HER). However, there have been few research on the creation of their three-phase heterojunctions and the associated HER process. Herein, we constructed a three-phase heterostructure sample consisting of orthorhombic CoSe₂ , cubic CoSe₂ and MoSe₂ and we investigated its HER performance. The sample shows microsphere morphology composed of nanosheets with interfacial interactions between the components. It possesses an overpotential of -136 mV at -10 mA cm^-2 in acid medium, which is superior to that of single component and most two-phase heterostructures. Especially, the overpotential at -200 mA cm^-2 is smaller than that of Pt/C. The excellent performance can be attributed to the d-orbital upshift of the Co active sites due to charge redistribution between the three-phase heterojunction and the optimization of the hydrogen free energy. This work provides inspiration for exploring the application of other multi-component heterojunctions in electrocatalytic hydrogen evolution.

Spatial Relation Controllable Di-Defects Synergy Boosts Electrocatalytic Hydrogen Evolution Reaction over VSe2 Nanoflakes in All pH Electrolytes

Defect engineering of transition metal dichalcogenides (TMDCs) is important for improving electrocatalytic hydrogen evolution reaction (HER) performance. Herein, a facile and scalable atomic-level di-defect strategy over thermodynamically stable VSe₂ nanoflakes, yielding attractive improvements in the electrocatalytic HER performance over a wide electrolyte pH range is reported. The di-defect configuration with controllable spatial relation between single-atom (SA) V defects and single Se vacancy defects effectively triggers the electrocatalytic HER activity of the inert VSe₂ basal plane. When employed as a cathode, this di-defects decorated VSe₂ electrocatalyst requires overpotentials of 67.2, 72.3, and 122.3 mV to reach a HER current density of 10 mA cm^-2 under acidic, alkaline, and neutral conditions, respectively, which are superior to most previously reported non-noble metal HER electrocatalysts. Theoretical calculations reveal that the reactive microenvironment consists of two adjacent SA Mo atoms with two surrounding symmetric Se vacancies, yielding optimal water dissociation and hydrogen desorption kinetics. This study provides a scalable strategy for improving the electrocatalytic activity of other TMDCs with inert atoms in the basal plane.

Interlayer Spacing Regulation of Molybdenum Selenide Promotes Electrocatalytic Hydrogen Evolution in Alkaline Media

The construction of heterostructures is a versatile tactic to enhance catalytic activity. However, it is still elusive to realize the modulation of the interlayer spacing in this way to further improve the performance. Here, strong interfacial coupling between CoSe₂ and MoSe₂ by constructing CoSe₂ /MoSe₂ heterostructures is achieved. The interlayer spacing of MoSe₂ is compressed by 0.3 Å. The enhanced charge transfer is validated by X-ray absorption spectroscopy and X-ray photoelectron spectroscopy. Coupled with the morphology of hollow microtubes, which can facilitate the exposure of active sites, CoSe₂ /MoSe₂ heterostructures reported here exhibit high activity (119 mV at 10 mA cm^-2 ) and excellent stability with small degradation after 50 h operation, surpassing other analogous powdered electrocatalysts. This work sheds light on the importance of tuning the interlayer spacing to improve electrocatalytic activity.

Heterostructures of tin and tungsten selenides for robust overall water splitting

Layered transition metal selenides have garnered increased attention in recent times as non-noble metal bifunctional electrocatalysts for electrochemical water splitting. Tungsten diselenide @ tin diselenide heterostructures in the present study significantly increase the electrochemical performance of oxygen evolution reaction with a low overpotential of 250 mV at 10 mA cm^-2 and high stability for 16 h (8.9 % loss), hydrogen evolution reaction with a low overpotential of 180 mV at 10 mA cm^-2 with a 21.9% loss in 16 h. The overall water splitting using a lab-size electrolyzer shows a low cell voltage (1.52 V @ 10 mA cm^-2) and high durability for 50 h (15.2% loss @ 10 mA cm^-2 and 4.4% loss @ 50 mA cm^-2). As a result, the heterostructures have demonstrated their ability to handle multiple challenges in energy conversion systems due to their unique properties.

Constructing MoSe2/MoS2 and MoS2/MoSe2 inner and outer-interchangeable flower-like heterojunctions: A combined strategy of interface polarization and morphology configuration to optimize microwave absorption performance

Interfacial polarization and geometrical morphology play a significant role in the attenuation of electromagnetic (EM) wave. Herein, the two-dimensional (2D)/2D heterojunction with flower-like geometrical morphology is proposed and produced, which may simultaneously provide a large contact area for achieving strong interfacial polarization and activates more sites for the possible multiple EM wave reflection and scattering. By adopting a simple two-step hydrothermal method, MoSe₂/MoS₂and MoS₂/MoSe₂ inner and outer-interchangeable heterojunctions consisting of 2D MoSe₂ and MoS₂ nanosheets with flower-like geometrical morphology were successfully synthesized. The results revealed that the hydrothermal temperatures significantly impacted the flower-like geometrical morphology and MoS₂ content. By optimizing the microstructures, the designed MoSe₂/MoS₂ and MoS₂/MoSe₂ heterojunctions presented enhanced comprehensive EM wave absorption properties (EMWAPs), possessing strong absorption capability, wide absorption bandwidth and thin matching thicknesses. Generally, this work demonstrates that the optimized EMWAPs of designed heterojunctions mainly originate from the special interfaces and morphology configuration, which also paves a new way for the designing and synthesis of transition metal dichalcogenides-based heterojunction as a novel and desirable candidate for high-performance microwave absorbers.

Molybdenum disulfide composite materials with encapsulated copper nanoparticles as hydrogen evolution catalysts

In the current work, a series of molybdenum disulfide composite MCNTs@Cu@MoS₂ materials with high hydrogen evolution performance are prepared. In the hydrogen evolution reaction, their overpotential is as low as 225 mV at a current density of 10 mA cm⁻² in 1 M H₂SO₄ as electrolyte solution. This excellent catalytic activity has been ascribed to its lower electrical impedance and high double layer capacitance. The encapsulation of copper nanoparticles into MoS₂ crystals significantly reduces their resistance, enhancing the electron transfer rate during water electrolysis. Thereby, the introduction of conductive nanoparticles into semi-conductive catalyst crystals would be an efficient measure to improve their electrochemical catalytic activity in the hydrogen evolution reaction.

Encapsulation of copper nanoparticles by the electrochemical catalyst MoS₂ effectively improved its HER performance.

Effect of cobalt phosphide (CoP) vacancies on its hydrogen evolution activity via water splitting: a theoretical study

Defect engineering plays an important role in improving the performance of catalysts. To clarify the roles of Co and P vacancies in CoP for water splitting, a theoretical study based on density functional theory was carried out in this paper. The geometric and electronic structures, activity and stability of the CoP (101)B surface, CoP (101)B with the Co vacancy (Co_vac) and the P vacancy (P_vac) are investigated. The results indicate that the CoP (101)B surface with P_vac and Co_vac can enhance the electron transfer to the surface. The P_vac will upward shift the Co d-band center near the vacancy site, which promotes the adsorption of H on the Co atom. As a result, the bridge Co-Co sites near the vacancy become the active sites for the hydrogen evolution reaction (HER) (ΔG_H* = 0.01 eV). The loss of the Co atom also results in an upward shift of its d-band center, which will enhance the H adsorption on the adjacent Co sites. The unevenly distributed electrons due to the presence of vacancies on the surface cause spontaneous dissociation of H₂O molecules. Furthermore, the thermodynamic analysis and surface energy find that the CoP (101)B and (101)B facets with Co_vac and P_vac present good stability. The current work has shed light onto the mechanism of water splitting on the surface of phosphide with vacancies. Our study suggests that engineering vacancies on CoP is a feasible route to improve its catalytic activity.

Plant polyphenol-involved coordination assembly-derived Mo3Co3C/Mo2C/Co@NC with phase regulation and interface engineering for efficient hydrogen evolution reaction electrocatalysis

Heterostructured Mo3Co3C/Mo2C/Co@NC catalysts were obtained by the calcination of tannic acid ligand-assembled precursors, enabling enhanced HER electrocatalysis through phase and interface regulation.

Surface Selenylation Engineering for Construction of a Hierarchical NiSe2/Carbon Nanorod: A High-Performance Nonenzymatic Glucose Sensor

As glucose (Glu) is an essential substance for metabolism as well as a symbol to diagnose diabetes, the demand of Glu sensors has increased significantly in recent decades. In this work, a hierarchical Ni-based electrochemical enzyme-free Glu sensor, namely, NiSe₂/CNR (carbon nanorod), was engineered through a facile thermal treatment using dimethylglyoxime dinickel salt with selenium (Se) powder. The prepared NiSe₂/CNR not only subtly introduces a hierarchical structure with rod-like carbon nanorods and rock-like NiSe₂ nanoparticles, which are extremely helpful in offering a greater catalytic activity area and more catalytic active sites, but also incorporates the Se element to increase the inherent activity. The fabricated NiSe₂/CNR exhibits distinguished performance for Glu detection in alkaline electrolytes with linear ranges of 0.5-411 μM and 411 μM to 6.311 mM, high sensitivities of 3636 μA mM^-1 cm^-2 at low concentrations, and 2121 μA mM^-1 cm^-2 at high concentrations, as well as a low detection limit of 380 nM (S/N = 3). It also possesses favorable reproducibility, stability, and long-term storage capacity. The practical feasibility of NiSe₂/CNR was also validated by detecting Glu in human serum. Moreover, the prepared hierarchical NiSe₂/CNR is of general interest for the construction of hierarchical Ni-based sensors.

Fe(III) Ions-Assisted Aniline Polymerization Strategy to Nitrogen-Doped Carbon-Supported Bimetallic CoFeP Nanospheres as Efficient Bifunctional Electrocatalysts toward Overall Water Splitting

It remains an urgent demand and challenging task to design and fabricate efficient, stable, and inexpensive catalysts toward sustainable electrochemical water splitting for hydrogen production. Herein, we explored the use of Fe(III) ion-assisted aniline polymerization strategy to embed bimetallic CoFeP nanospheres into the nitrogen-doped porous carbon framework (referred CoFeP-NC). The as-prepared CoFeP-NC possesses excellent hydrogen evolution reaction (HER) performance with the small overpotential (η₁₀) of 81 mV and 173 mV generated at a current density of 10 mA cm^-2 in acidic and alkaline media, respectively. Additionally, it can also efficiently catalyze water oxidation (OER), which shows an ideal overpotential (η₁₀) of 283 mV in alkaline electrolyte (pH = 14). The remarkable catalytic property of CoFeP-NC mainly stems from the strong synergetic effects of CoFeP nanospheres and carbon network. On the one hand, the interaction between the two can make better contact between the electrolyte and the catalyst, thereby providing a large number of available active sites. On the other hand, it can also form a network to offer better durability and electrical conductivity (8.64 × 10^-1 S cm^-1). This work demonstrates an efficient method to fabricate non-noble electrocatalyst towards overall water splitting, with great application prospect.

New Water Oxidation Electrocatalyst Based on the Cobalt-Containing Polyoxometalate-Reduced Graphene Oxide Hybrid Nanomaterial

A new hybrid nanomaterial based on the immobilization of cobalt-containing polyoxometalate (CoPOM) on the surface of reduced graphene oxide (rGO) was designed for an efficient electrocatalytic water splitting reaction. First, the surface of rGO was functionalized with aminopropylsilyl groups and protonated with hydrochloric acid to produce ammonium groups. Then, the electrostatic interaction of positively charged rGO-supported ammonium groups with anionic CoPOM produced a CoPOM-APTS-rGO hybrid nanomaterial. The achieved hybrid nanomaterial exhibited a low overpotential of 128 mV versus NHE at a current density of 10 mA cm^-2 in the electrocatalytic water oxidation at pH 7. In addition, a fast reaction kinetic with a Tafel slope of 74 mV dec^-1 was seen in the presence of the prepared hybrid nanomaterial. Linear sweep voltammetry analysis revealed the long-term stability and activity of CoPOM-APTS-rGO for water oxidation in neutral conditions.

Fabrication of Nonmetal-Modulated Dual Metal-Organic Platform for Overall Water Splitting and Rechargeable Zinc-Air Batteries

The fast development of portable water-splitting devices has led to a great deal of work on rechargeable metal-air batteries or solar cells; however, the lack of affordable multifunctional electrocatalysts still hampers their widespread applications. Herein, a well-aligned ternary metal (oxy)hydroxide nanostructure is a sacrificial pseudomorphic transformation template of an integrated metal-organic network on the carbon cloth (CC) surface, that is, the Fe-doped metal-organic framework (MOF) ZnNiCoSe@CC nanosheet network, exhibiting powerful and efficient multifunctional electrocatalysts such as the oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction in alkaline media combined with desirable electrode kinetics. As a proof-of-concept observational study, the nanostructured Fe-doped MOF ZnNiCoSe@CC could be used as air-cathode materials in the rechargeable metal-air battery. The fabricated device delivered higher open-circuit voltage, higher capacity, and peak power density, excellent discharge-charge performance, and long cycle life. Thus, our research creates a unique perspective on the development of highly portable air electrodes with a favorable electrocatalytic application of overall water-splitting reaction.

FeNi3-modified Fe2O3/NiO/MoO2 heterogeneous nanoparticles immobilized on N, P co-doped CNT as an efficient and stable electrocatalyst for water oxidation

As a rate-determining step, electrocatalytic water oxidation acts a pivotal role in the water splitting process. As a consequence, it is of great significance to explore low-cost, efficient and durable electrocatalysts for the oxygen evolution reaction (OER) to promote electrocatalytic splitting water. Herein, for the first time, FeNi₃-modified Fe₂O₃/NiO/MoO₂ heterogeneous nanoparticles immobilized on N, P co-doped CNT matrix materials (FNM/NPCNT) are synthesized via a facile solid-phase grinding of the precursor, composed of nickel hexacyanoferrate/phosphomolybdic acid/CNT, and subsequently pyrolyzing under nitrogen atmosphere without any further post-processing. Due to its significant enhancement of the charge transfer efficiency and prevention of the metallic-based catalysts from being corroded, the as-prepared FNM/NPCNT hybrid electrocatalyst shows a high OER activity with a low overpotential of 282 mV vs. RHE at 10 mA cm^-2 and a small Tafel slope of 46.2 mV dec^-1 in an alkaline electrolyte. Moreover, the as-prepared FNM/NPCNT hybrid delivers a large mass activity of 327.6 A g^-1 at the potential of 1.7 V and excellent stability (more than 20 h). This study opens up a new approach to design and synthesize non-precious transition metal-based composites immobilized N, P co-doped CNT materials as OER catalysts with high efficiency and long-term stability for promoting water splitting.

CoSe2 hollow microspheres, nano-polyhedra and nanorods as pseudocapacitive Mg-storage materials with fast solid-state Mg2+ diffusion kinetics

CoSe₂ materials with different nanostructures are used as pseudocapacitive Mg-storage cathodes, which exhibit fast solid-state Mg²⁺ ions diffusion kinetics. In this work, CoSe₂ with different nanostructures including hollow microspheres (H-CoSe₂), nano-polyhedra (P-CoSe₂) and nanorods (R-CoSe₂) are fabricated by using facile one-step hydrothermal methods, and used as pseudocapacitive electrodes for rechargeable Mg batteries. It is observed that R-CoSe₂ exhibits the highest reversible capacity of 233 mA h g^-1 at 50 mA g^-1 and an excellent rate capability of 116 mA h g^-1 at 500 mA g^-1, ascribing to the 1D nanorod structure which facilitates the solid-state Mg²⁺ diffusion. Benefitting from the stable hierarchical structure, H-CoSe₂ exhibits a superior long-term cycling stability of 350 cycles. A mechanism study indicates that the redox reaction reversibly occurs between CoSe₂ and metallic Co⁰. Further investigation demonstrates that the fast solid-state Mg²⁺ diffusion kinetics and surface-controlled pseudocapacitive behavior enhance the electrochemical performance. This work highlights a novel and efficient Mg-storage strategy of using pseudocapacitive materials, and the performance and solid-state Mg²⁺ diffusion kinetics of CoSe₂ could be optimized by rational structural tailoring.

CoSe2 nanobelt coupled with CoMoO4 nanosheet as efficient electrocatalysts for hydrogen and oxygen evolution reaction

Designing non-noble electrocatalysts with low-cost and efficient is crucial to the development of sustainable and clean energy resources. Here, we synthesized a novel S–CoSe2/CoMoO4 and O–CoSe2/CoMoO4hybrid electrocatalysts for the HER and OER, respectively. Possibly due to the synergetic chemical coupling effects between CoSe2/DETA and CoMoO4, and the introduction of S heteroatom and oxygen vacancy, this hybrid could expose enough active edges, and then promoted the constructed hybrid displayed superior hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalytic performance. The S–CoSe2/CoMoO4 sample afforded a current density of 10 ​mAcm-2 at a small overpotential of 177 ​mV and a small Tafel slope of 54 ​mV dec−1. Moreover, the oxidized CoSe2/CoMoO4 (O–CoSe2/CoMoO4) also displayed a remarkable catalytic property for OER with a small Tafel slope of 43 ​mV dec−1, as well as excellent stability in 1.0 ​M KOH. Therefore, this noble-metal-free and highly efficient catalyst enables prospective applications for electrochemical applications.

•The novel S-CoSe2/CoMoO4 and O-CoSe2/CoMoO4 hybrid electrocatalysts are reported. •The oxygen vacancy resulted in O-CoSe2/CoMoO4 displayed excellent stability for OER. •This non-noble based electrocatalysts are valuable for the future clean energy.

3D hollow Co-Fe-P nanoframes immobilized on N,P-doped CNT as an efficient electrocatalyst for overall water splitting

The rational design of nonprecious and high-efficiency bifunctional electrocatalysts with advanced structural and compositional preponderance for water electrolysis is of paramount importance for the generation of sustainable and clean energy. Herein, for the first time, a novel three-dimensional (3D) hollow hybrid electrocatalyst, Co-Fe-P nanoframe immobilized on N,P-doped carbon nanotubes (CoFeP NFs/NPCNT), was synthesized by selectively etching a CNT-composited Co,Fe-based Prussian blue analogue and subsequent phosphorization. Benefiting from its unique 3D hollow nanoarchitecture, which offers rich porosity and abundant catalytically active sites and guarantees excellent conductivity and structural stability, the hollow CoFeP NFs/NPCNT hybrid delivered pronounced catalytic activity for oxygen evolution (or hydrogen evolution) in alkaline electrolyte, with a low overpotential of 278 (or 132) mV at 10 mA cm-2, small Tafel slope of 39.5 (or 62.9) mV dec-1 and prominent long-term stability. Therefore, when CoFeP NFs/NPCNT was employed as the cathode and anode toward overall water-splitting, it required a quite small cell voltage of only 1.56 V to afford a current density of 10 mA cm-2, and displayed outstanding electrocatalytic stability over 60 h, greatly approaching the performance of the commercial Pt/C(-)//RuO2(+) electrolyzer and outperforming most other non-noble-based electrolyzers.

Hierarchically Porous W-Doped CoP Nanoflake Arrays as Highly Efficient and Stable Electrocatalyst for pH-Universal Hydrogen Evolution

It is still challenging to develop high-efficiency and low-cost non-noble metal-based electrocatalysts for hydrogen evolution reaction (HER) in pH-universal electrolytes. Herein, hierarchically porous W-doped CoP nanoflake arrays on carbon cloth (W-CoP NAs/CC) are synthesized via facile liquid-phase reactions and a subsequent phosphorization process. The W-CoP NAs/CC hybrid can be directly employed as a binder-free electrocatalyst and delivers superior HER performance in pH-universal electrolytes. Especially, it delivers very low overpotentials of 89, 94, and 102 mV to reach a current density of 10 mA cm^-2 in acidic, alkaline, and neutral electrolytes, respectively. Furthermore, it shows a nearly 100% Faradaic efficiency as well as superior long-term stability with no decreasing up to 36 h in pH-universal electrolytes. The outstanding electrocatalytic performance of W-CoP NAs/CC can be mainly attributed to the porous W-doped nanoflake arrays, which not only afford rich exposed active sites, but also accelerate the access of electrolytes and the diffusion of H₂ bubbles, thus efficiently promoting the HER performance. This work provides a new horizon to rationally design and synthesize highly effective and stable non-noble metal phosphide-based pH-universal electrocatalysts for HER.

Facile synthesis of Cu2MoS4 nanosheet/multi-walled carbon nanotube composites as a high-efficiency electrocatalyst for hydrogen evolution

A Cu₂MoS₄/MWCNT electrocatalyst with enhanced HER performance was synthesized for the first time, in which Cu₂MoS₄ nanosheets are intimately interlinked by MWCNTs.