Metal Doping Effect of the M-Co2P/Nitrogen-Doped Carbon Nanotubes (M = Fe, Ni, Cu) Hydrogen Evolution Hybrid Catalysts

Hydrogen storage efficiency of Fe doped carbon nanotubes: molecular simulation study

Given that adsorption is widely regarded as a favorable technique for hydrogen storage, it is appropriate to pursue the development of suitable adsorbent materials for industrial storage. This study aimed to assess the potential of Fe-doped carbon nanotubes (FeCNT) as a remarkable material for hydrogen storage. The structures of pure and Fe-doped CNTs were optimized based on quantum mechanical calculations using density functional theory (DFT) with the Perdew-Burke-Ernzerhof (PBE) method. To gain a comprehensive understanding of the adsorption behavior, Monte Carlo simulation was employed to investigate the adsorption of hydrogen molecules on FeCNT. The study specifically examined the impact of temperature, pressure, and hydrogen mole percentage on the adsorption capacity of FeCNT. The findings indicated that the uptake of hydrogen increased as the pressure increased, and when the pressure exceeded 5 MPa, FeCNT reached a state of near saturation. At room temperature and pressures of 1 and 5 MPa, the hydrogen capacities of FeCNT were determined to be 1.53 and 6.92 wt%, respectively. The radial distribution function diagrams confirmed the formation of a one-layer adsorption phase at pressures below 5 MPa. A comparison of the temperature dependence of hydrogen adsorption between FeCNT and pure CNT confirmed the effectiveness of Fe doping in hydrogen storage up to room temperature. FeCNT exhibited a greater reduction in initial hydrogen capacity at temperatures above room temperature. To evaluate the safety of the system, the use of N2 as a dilution agent was investigated by examining the hydrogen uptake of FeCNT from pure and H2/N2 mixtures at 300 K. The results showed that the addition of N2 to the environment had no significant effect on FeCNT hydrogen storage at pressures below 4 MPa. Furthermore, the study of H2 selectivity from the H2/N2 mixture indicated that FeCNT demonstrated a preference for adsorbing H2 over a wide range of bulk mole fractions at pressures of 4 and 5 MPa, suggesting that these pressures could be considered optimal. Under these conditions, Fe doping can offer an efficient and selective adsorption surface for hydrogen storage.

A reverse electrodialysis cell-modified photocatalytic fuel cell for efficient electricity and hydrogen generation from the degradation of refractory organic pollutants

Wastewater treatment is typically energy-intensive. To achieve carbon neutrality, new wastewater treatment technologies that have high efficiency and low energy consumption must be developed. In this study, a reverse electrodialysis (RED) cell-modified photocatalytic fuel cell (PRC) for efficient electricity and hydrogen generation from the degradation of refractory organic pollutants is developed and evaluated. A hydrogen evolution cathode was developed and optimized by doping 1.53 wt. % Ni-N-C on CoP/NF. The bias voltage generated from the RED stack accelerated the separation of photoinduced holes and electrons on the photoanode, which enhances ampicillin (AMP) degradation and hydrogen production. The RED stack and electrode reactions respectively contribute 72.3 % and 27.7 % to the electricity production of PRC. The output current and cumulative hydrogen generation reach 2.2-3.0 mA and 500 μmol/L respectively with 81.8 % AMP removal. Increasing high concentration (HC), flow rate of NH₄HCO₃ solutions and AMP concentration could increase the electricity and hydrogen generation. Acidic environment is helpful to improve the reaction rate of hydrogen evolution. We believe this study would provide a promising option for wastewater remediation.

Recent Advances and Future Perspectives of Metal-Based Electrocatalysts for Overall Electrochemical Water Splitting

Recently, the growing demand for a renewable and sustainable fuel alternative is contingent on fuel cell technologies. Even though it is regarded as an environmentally sustainable method of generating fuel for immediate concerns, it must be enhanced to make it extraordinarily affordable, and environmentally sustainable. Hydrogen (H₂ ) synthesis by electrochemical water splitting (ECWS) is considered one of the foremost potential prospective methods for renewable energy output and H₂ society implementation. Existing massive H₂ output is mostly reliant on the steaming reformation of carbon fuels that yield CO₂ together with H₂ and is a finite resource. ECWS is a viable, efficient, and contamination-free method for H₂ evolution. Consequently, developing reliable and cost-effective technology for ECWS was a top priority for scientists around the globe. Utilizing renewable technologies to decrease total fuel utilization is crucial for H₂ evolution. Capturing and transforming the fuel from the ambient through various renewable solutions for water splitting (WS) could effectively reduce the need for additional electricity. ECWS is among the foremost potential prospective methods for renewable energy output and the achievement of a H₂ -based economy. For the overall water splitting (OWS), several transition-metal-based polyfunctional metal catalysts for both cathode and anode have been synthesized. Furthermore, the essential to the widespread adoption of such technology is the development of reduced-price, super functional electrocatalysts to substitute those, depending on metals. Many metal-premised electrocatalysts for both the anode and cathode have been designed for the WS process. The attributes of H₂ and oxygen (O₂ ) dynamics interactions on the electrodes of water electrolysis cells and the fundamental techniques for evaluating the achievement of electrocatalysts are outlined in this paper. Special emphasis is paid to their fabrication, electrocatalytic performance, durability, and measures for enhancing their efficiency. In addition, prospective ideas on metal-based WS electrocatalysts based on existing problems are presented. It is anticipated that this review will offer a straight direction toward the engineering and construction of novel polyfunctional electrocatalysts encompassing superior efficiency in a suitable WS technique.

Synergistically Coupling of Manganese-Doped CoP Nanowires Arrays with Highly Dispersed Ni(PO3)2 Nanoclusters toward Efficient Overall Water Splitting

Co-based phosphides are considered to be highly promising electrocatalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, their electrocatalytic efficiencies are greatly limited by the weak water dissociation process and unsatisfactory adsorption ability toward reaction intermediates. Herein, novel Mn-doped CoP/Ni(PO₃)₂ heterostructure array electrocatalysts which are composed of highly dispersed Ni(PO₃)₂ nanoclusters that are tightly wrapped on Mn-doped CoP nanowire arrays are designed. An electrocatalytic performance test suggested that the heterostructure arrays exhibited competitive electrocatalytic performance toward both HER and OER, which needed overpotentials of 116 and 245 mV to drive a current of 10 mA/cm², respectively. Encouragingly, a symmetric two electrode water splitting system constructed by the heterostructure arrays required an ultralow cell voltage, suggesting the potential in overall water splitting. First-principles calculations combined with experimental characterization were further performed to clarify the electrocatalytic mechanism. On the one hand, effective doping of Mn atoms could optimize the surface electronic structure of CoP and promote the intrinsic activity. On the other hand, the compact and abundant heterogeneous interface between Ni(PO₃)₂ and CoP not only made more active sites exposed but also promoted the effective adsorption of intermediate reaction species on the catalyst surface. This work provides a new strategy to improve electrocatalytic performance of Co-based phosphides through the synergistic coupling of metal-doping and phosphate surface decoration, which will greatly promote the development of highly efficient electrocatalysts for overall water splitting.

High-performance self-supporting AgCoPO4/CFP for hydrogen evolution reaction under alkaline conditions

Electrochemical water decomposition to produce hydrogen is a promising approach for renewable energy storage. It is vital to develop a catalyst with low overpotential, low cost and high stability for hydrogen evolution reaction (HER) under alkaline conditions. Herein, we used a simple hydrothermal method to obtain a AgCo(CO)₄ precursor on the surface of carbon fiber paper (CFP). After thermal phosphorization, the self-supporting catalyst AgCoPO₄/CFP was obtained, which greatly improved the HER catalytic performance under alkaline conditions. At 10 mA cm^-2, it showed an overpotential of 32 mV. The Tafel slope was 34.4 mV dec^-1. The high catalytic performance of AgCoPO₄/CFP may be due to the hydrophilic surface promoting effective contact with the electrolyte and the synergistic effect of the two metals, which accelerated electron transfer and thus promoted hydrogen evolution reaction. In addition, it showed an outstanding urea oxidation reaction (UOR) activity. After adding 0.5 M urea, the over-potential of the AgCoPO₄/CFP assembled electrolytic cell was only 1.45 V when the current density reached 10 mA cm^-2, which was much lower than that required for overall water splitting. This work provides a new method for the design and synthesis of efficient HER electrocatalysts.

Robust visible-light photocatalytic H2 evolution on 2D RGO/Cd0.15Zn0.85In2S4–Ni2P hierarchitectures

Unique 2D ternary hierarchitectures constructed from reduced graphene oxide nanosheets grown with ultrathin Cd0.15Zn0.85In2S4 nanosheets and Ni2P nanoparticles exhibited an outstanding capability for visible-light photocatalytic H2 production.

Electronic Structure and d-Band Center Control Engineering over Ni-Doped CoP3 Nanowall Arrays for Boosting Hydrogen Production

To address the challenge of highly efficient water splitting into H₂, successful fabrication of novel porous three-dimensional Ni-doped CoP₃ nanowall arrays on carbon cloth was realized, resulting in an effective self-supported electrode for the electrocatalytic hydrogen-evolution reaction. The synthesized samples exhibit rough, curly, and porous structures, which are beneficial for gaseous transfer and diffusion during the electrocatalytic process. As expected, the obtained Ni-doped CoP₃ nanowall arrays with a doping concentration of 7% exhibit the promoted electrocatalytic activity. The achieved overpotentials of 176 mV for the hydrogen-evolution reaction afford a current density of 100 mA cm⁻², which indicates that electrocatalytic performance can be dramatically enhanced via Ni doping. The Ni-doped CoP₃ electrocatalysts with increasing catalytic activity should have significant potential in the field of water splitting into H₂. This study also opens an avenue for further enhancement of electrocatalytic performance through tuning of electronic structure and d-band center by doping.

Heteroatom-Doping of Non-Noble Metal-Based Catalysts for Electrocatalytic Hydrogen Evolution: An Electronic Structure Tuning Strategy

Electrocatalytic water splitting for hydrogen production is an appealing way to reduce carbon emissions and generate renewable fuels. This promising process, however, is limited by its sluggish reaction kinetics and high-cost catalysts. Construction of low-cost and high-performance non-noble metal-based catalysts have been one of the most effective approaches to address these grand challenges. Notably, the electronic structure tuning strategy, which could subtly tailor the electronic states, band structures, and adsorption ability of the catalysts, has become a pivotal way to further enhance the electrochemical water splitting reactions based on non-noble metal-based catalysts. Particularly, heteroatom-doping plays an effective role in regulating the electronic structure and optimizing the intrinsic activity of the catalysts. Nevertheless, the reaction kinetics, and in particular, the functional mechanisms of the hetero-dopants in catalysts yet remains ambiguous. Herein, the recent progress is comprehensively reviewed in heteroatom doped non-noble metal-based electrocatalysts for hydrogen evolution reaction, particularly focus on the electronic tuning effect of hetero-dopants in the catalysts and the corresponding synthetic pathway, catalytic performance, and activity origin. This review also attempts to establish an intrinsic correlation between the localized electronic structures and the catalytic properties, so as to provide a good reference for developing advanced low-cost catalysts.

Regioselective Construction of Chemically Transformed Phosphide-Metal Nanoheterostructures for Enhanced Hydrogen Evolution Catalysis

Engineering nanoheterostructures (NHs) plays a key role in exploring novel or enhanced physicochemical properties of nanocrystals. Despite previously reported synthetic methodologies, selective synthesis of NHs to achieve the anticipated composition and interface is still challenging. Herein, we presented a colloidal strategy for the regioselective construction of typical Ag-Co₂P NHs with precisely controlled location of Ag nanoparticles (NPs) on unique chemically transformed Co₂P nanorods (NRs) by simply changing the ratio of different surfactants. As a proof-of-concept study, the constructed heterointerface-dependent hydrogen evolution reaction (HER) catalysis was demonstrated. The multiple Ag NP-tipped Co₂P NRs exhibited the best HER performance, due to their more exposed active sites and the synergistic effect at the interfaces. Our results open up new avenues in rational design and fabrication of NHs with delicate control over the spatial distribution and interfaces between different components.

N-Doped carbon-coated Co2P-supported Au nanocomposite as the anode catalyst for borohydride electrooxidation

Au₍₅₀₎Co₂P@NC₍₅₀₎/C nanoparticle composite electrocatalyst combines the lower content of noble metal and much higher catalytic activity for BH₄⁻ electrooxidation.

V-Doped CoP Nanosheet Arrays as Highly Efficient Electrocatalysts for Hydrogen Evolution Reaction in Both Acidic and Alkaline Solutions

It is of significant necessity to explore inexpensive and high-active electrocatalysts toward hydrogen evolution reaction (HER) in both acidic and basic media. In this work, V-doped CoP nanosheet arrays supported on the carbon cloth (V-CoP/CC) are fabricated though a facile water-bath/phosphorization method. The nanoarray structure on the three-dimensional self-supporting electrode can provide a large electrochemical active surface area with more exposed active sites to accelerate the reaction kinetics. Furthermore, V doping is able to tune the electronic properties and thus enhance the intrinsic catalytic activity of CoP. Consequently, the V-CoP/CC electrode exhibits excellent electrocatalytic activities toward HER in both 0.5 M H₂SO₄ and 1 M KOH solutions with small overpotentials of 88 and 98 mV at a current density of 10 mA cm⁻², respectively. The present work will offer a feasible way to tailor the catalytic activity by hetero-atoms doping toward HER.

Three-dimensionally hierarchical NiCoP@PANI architecture for high-performance hydrogen evolution reaction

Ternary phosphides are attracting great attention in the field of electrocatalytic hydrogen evolution and they have been verified to be highly active for water splitting. Herein, we developed polyaniline (PANI) coated nickel-cobalt metal phosphides nanowire arrays grown on nickel foam (NiCoP@PANI) as hydrogen evolution reaction electrocatalysts. The appearance of PANI with excellent electric conductivity can accelerate H⁺ in electrolyte transfer into H₂ and offer a masking layer to restrain the damage of electrode structural. Besides, the 3D porous structural of nickel foam can act as a skeleton to avoid electrode structure collapse and a channel for electron transfer. The optimized NiCoP@PANI can drive a current density of 10 mA cm^-2 at low overpotential of 80.6 mV in 1 M KOH solution, and satisfactory electrochemical stability with unbroken structure and unchanged composition after electrochemical test.

Controllable Heteroatom Doping Effects of CrxCo2-xP Nanoparticles: a Robust Electrocatalyst for Overall Water Splitting in Alkaline Solutions

The effect of doping Cr on the electrocatalytic activity of Co₂P supported on carbon black (Cr_xCo_2-xP/CB) for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution was investigated. A beneficial improvement in the performance of Co₂P toward HER and OER was discovered. For the HER at -200 mV overpotential, the turnover frequency (TOF) increases almost 6-fold from 0.26 to 1.52 electron site_Co^-1 s^-1 when Co₂P/CB has a small amount of Cr added to form Cr_0.2Co_1.8P/CB. Similarly, we estimate an increase from 0.205 to 0.585 electron site_Co^-1 s^-1 for the OER at 1.6 V for the same change in composition. With 10 atom % Cr doping, the Cr_0.2Co_1.8P/CB catalyst needed 226 mV overpotential to produce a cathodic current density of -100 A g_Co^-1 and 380 mV overpotential to produce an anodic current density of 100 A g_Co^-1. Based on both experimental results and theoretical calculations, the activity improvement results from optimization of the electronic properties of Co₂P after Cr doping.

Ultrathin Nanosheet-Assembled Co-Fe Hydroxide Nanotubes: Sacrificial Template Synthesis, Topotactic Transformation, and Their Application as Electrocatalysts for Efficient Oxygen Evolution Reaction

Hydrogen as a reliable, sustainable, and efficient energy carrier can effectively alleviate global environmental issues and energy crisis. However, the electrochemical splitting of water for large-scale hydrogen generation is still impeded by the sluggish kinetics of the oxygen evolution reaction (OER) at the anode. Considering the synergistic effect of Co and Fe on the improvement of OER catalytic activity, we prepared Co-Fe hydroxide nanotubes through a facile sacrificial template route. The resultant Co_0.8Fe_0.2 hydroxide nanotubes exhibited remarkable electrocatalytic performance for OER in 1.0 M KOH, with a small overpotential of about 246 mV at 10 mA cm^-2 and a Tafel slope of 53 mV dec^-1. The Co_0.8Fe_0.2P nanotubes were further prepared by a phosphidation treatment, exhibiting excellent OER catalytic performance with an overpotential as low as 240 mV at 10 mA cm^-2. Besides, the Co_0.8Fe_0.2P nanotubes supported on a Ni foam (Co_0.8Fe_0.2P/NF) used as both positive and negative poles in a two-electrode system achieved a cell voltage of about 1.67 V at 10 mA cm^-2 and exhibited outstanding stability. A water splitting system was constructed by Co_0.8Fe_0.2P/NF electrodes connected with a crystalline silicon solar cell, demonstrating the application as an electrocatalyst.

Metal-organic frameworks derived carbon-incorporated cobalt/dicobalt phosphide microspheres as Mott-Schottky electrocatalyst for efficient and stable hydrogen evolution reaction in wide-pH environment

Cobalt phosphides, as low cost and abundant non-noble materials for hydrogen evolution reaction (HER), are always constrained by their inferior charge transfer and sluggish intrinsic electrocatalytic kinetics. In this work, carbon-incorporated Co/Co₂P microspheres (Co/Co₂P@C) as a novel Mott-Schottky catalyst were synthesized successfully via carbonization and gradual phosphorization of Co based metal-organic frameworks. The unique merits, including Mott-Schottky effect at the interface formed between metal Co and semiconductor Co₂P, the incorporated carbon-layer on the surface and the spherical structure endow Co/Co₂P@C with favorable electrical conductivity, preferable kinetics and long-term stability when it was evaluated as electrocatalyst for HER in wide-pH range. As a result, the Co/Co₂P@C with the optimized phosphorization degree delivers a benchmark current density of 10 mA cm^-2 at the low overpotential of 192 and 158 mV in acidic and alkaline electrolytes, respectively, with a remarkable stability (CV cycling for 3000 cycles and continuous electrolysis at the overpotential of 200 mV for 48 h). Therefore, the as-designed Co/Co₂P@C should be one of the most promising catalysts for HER application.

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.

Probing into the effect of heterojunctions between Cu/Mo2C/Mo2N on HER performance

Hydrogen is one of the cleanest forms of energy and can solve several issues, including environmental pollution and depletion of fossil fuels.

Hierarchical Bimetallic Ni-Co-P Microflowers with Ultrathin Nanosheet Arrays for Efficient Hydrogen Evolution Reaction over All pH Values

Designing efficient nonprecious catalysts with pH-universal hydrogen evolution reaction (HER) performance is of importance for boosting water splitting. Herein, a self-template strategy based on Ni-Co-glycerates is developed to prepare bimetallic Ni-Co-P microflowers with ultrathin nanosheet arrays. The highly porous core-shell structure gives rise to affluent mass transfer channels and availably prevents the aggregation of nanosheets, while the ultrathin nanosheets are favorable for producing abundant active sites. Besides, the produced CoP/NiCoP heterostructure in the bimetallic Ni-Co-P catalyst has excellent HER performance in a wide pH range. The as-prepared catalyst shows low potentials of 90, 157, and 121 mV to deliver a current density of 10 mA cm^-2 in 0.5 M H₂SO₄, 0.5 M PBS, and 1 M KOH solution, respectively. Meanwhile, negligible overpotential decay is achieved in the polarization curves after a long-term stability determination. This work supplies a promising strategy for developing pH-universal HER electrocatalysts based on solid-state metal alkoxides.

Converting surface-oxidized cobalt phosphides into Co2(P2O7)-CoP heterostructures for efficient electrocatalytic hydrogen evolution

Exploring noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) is a key issue in a hydrogen economy blueprint. As one of the promising candidates, transition metal phosphides unfortunately suffer from inevitable surface oxidation which obstructs active-site exposure. Herein, a facile reduction followed by a surface phosphorization is introduced to convert surface-oxidized cobalt phosphides to a Co₂(P₂O₇)-CoP heterostructure embedded in N-doped carbon (Co₂(P₂O₇)-CoP/NC), accomplishing an efficient HER in both acidic and alkaline electrolytes. It affords low overpotentials (η ₁₀) of 88 and 97 mV to reach a current density of -10 mA cm^-2, and small Tafel slopes of 51 and 61 mV dec^-1 in 0.5 M H₂SO₄ and 1.0 M KOH, respectively, outperforming the parent surface-oxidized Co₂P and most previously-reported Pt-free electrocatalysts. The remarkably improved electrocatalysis should be ascribed to the strong surface acidity of the Co₂(P₂O₇) component and thereby the promoted HER kinetics on Co₂(P₂O₇)-CoP interfaces. This work will encourage the development of cost-efficient electrocatalysts via surface engineering.

F or V-induced activation of (Co, Ni)2P during electrocatalysis for efficient hydrogen evolution reaction

A series of (Co, Ni)₂P–xF and post-(Co, Ni)₂P–xF electrocatalysts with different compositions, morphologies and HER performances were synthesized. Among them, post-(Co, Ni)₂P–10F exhibits the best HER activity.

Simple vapor–solid-reaction route for porous Cu2O nanorods with good HER catalytic activity

Porous Cu₂O nanorods with good HER catalytic performance were synthesized by a simple vapor–solid reaction between Cu(OH)₂ and ethylene glycol.

Enhancing hydrogen evolution activity by doping and tuning the curvature of manganese-embedded carbon nanotubes

Doping heteroatoms (Mn and N) and tuning the curvature of carbon nanotubes could efficiently elevate the C p-band center, lower the absolute electrode potential, and thus enhance the HER performance.

WSe2 nanoparticles with enhanced hydrogen evolution reaction prepared by bipolar electrochemistry: application in competitive magneto-immunoassay

Among groups of layered nanomaterials, transition metal dichalcogenides (TMDs) are the most studied group, especially for their hydrogen evolution reaction (HER) electrocatalytic activity and good stability in a highly corrosive environment. However, TMDs possess only low catalytic activity in the bulk form consisting of 2H phase, therefore, exfoliation must take place to enlarge the surface area and create new catalytically active sites (edges and defects). The most common exfoliation routes use organometallic reagents, such as tert-butyllithium (t-BuLi). Recently, bipolar electrochemistry (BE) was reported as a new efficient exfoliation and down-sizing technique applied on several layered materials. In this work, we used BE for further down-sizing of WSe2 micro-sheets, which were pre-exfoliated using tert-bulyllithium intercalator, down to nanoparticles (NPs). These WSe2 NPs outperformed t-BuLi exfoliated particles in terms of the overpotential needed for HER electrocatalysis. Moreover, WSe2 NPs were used effectively as a label for a competitive magneto-inmunoassay. This competitive magneto-immunoassay offers high selectivity with a wide linearity range, high sensitivity and a low limit of detection. We believe that such labels possess a great potential for bioassays.

Ruthenium Incorporated Cobalt Phosphide Nanocubes Derived From a Prussian Blue Analog for Enhanced Hydrogen Evolution

Electrochemical water splitting in alkaline media plays an important role in mass production of hydrogen. Ruthenium (Ru), as the cheapest member of platinum-group metals, has attracted much attention, and the incorporation of trace amount of Ru with cobalt phosphide could significantly improve the hydrogen evolution reaction (HER) catalytic activity. In this work, ruthenium-incorporated cobalt phosphide nanocubes are synthesized via a reaction between Co-Co Prussian blue analog (Co-PBA) and ruthenium chloride (RuCl3) followed by the phosphidation. The sample with a Ru content of ~2.04 wt.% exhibits the best HER catalytic activity with a low overpotential of 51 and 155 mV, to achieve the current densities of -10 and -100 mA cm-2, respectively, and the Tafel slope of 53.8 mV dec-1, which is comparable to the commercial Pt/C. This study provides a new perspective to the design and construction of high performance electrocatalysts for HER and other catalytic applications in a relatively low price.

Epitaxial growth of Ni(OH)2 nanoclusters on MoS2 nanosheets for enhanced alkaline hydrogen evolution reaction

Constructing heterostructures is an effective strategy for designing efficient electrocatalysts. MoS2 is a star catalyst for hydrogen evolution reaction (HER) in acidic media; however, the alkaline HER activity is deficient due to the sluggish water dissociation process. Herein, Ni(OH)2/MoS2 heterostructures with Ni(OH)2 nanoclusters epitaxially decorated on the surface of MoS2 are synthesized towards the alkaline HER. As compared with MoS2, the epitaxial Ni(OH)2/MoS2 heterostructures show significantly enhanced HER activity in 1 M KOH, and the overpotential is decreased by nearly 150 mV to reach a current density of 10 mA cm-2. The substantial increase in turnover frequency (TOF) demonstrates that the intrinsic activity is greatly improved after the incorporation of Ni(OH)2 nanoclusters. The presence of Ni(OH)2 nanoclusters would provide additional water dissociation sites while MoS2 is ready for the adsorption and combination of the generated H*, and this so-called synergistic effect eventually induces significantly enhanced alkaline HER kinetics. Besides, the electron transfer from Ni(OH)2 to MoS2 increases the proton affinity of MoS2. The present results describe an interesting case of an atomic-scale electrochemically inert material promoted HER process, and would open a new avenue into designing efficient hetero-nanostructures towards electrocatalytic applications.

Facile Electrodeposition of Ni-Cu-P Dendrite Nanotube Films with Enhanced Hydrogen Evolution Reaction Activity and Durability

Hydrogen can be the potential substitute energy carrier for fuel while electrolysis water with hydrogen evolution reaction (HER) is an efficient way to produce hydrogen. Highly active and robust electrocatalysts composed by earth abundant elements are required. Herein, nickel-copper-phosphorus (Ni-Cu-P) electrocatalysts are designed and synthesized by a facile one-step electrodeposition method. A unique pine-needle-like dendrite nanotube morphology of Ni-Cu-P electrocatalyst can be synthesized when copper content changed and impressive HER activity obtained in alkaline and acidic media. Briefly, the overpotential reaches 120 mV in 1 M KOH and 150 mV in 0.5 M H₂SO₄ at the current density of 10 mA cm^-2, with the corresponding Tafel slope reaching 69 mV dec^-1. The results are close to that of commercial Pt/C catalysts (37 mV in 1 M KOH). Furthermore, the density functional theory calculations also demonstrate that P-incorporated Ni-Cu, Cu-incorporated Ni-P, and Ni-incorporated Cu-P have the optimized hydrogen adsorption free energy (Δ G_H*) of -0.066, -0.157, and -0.003 eV, respectively, which are more suitable than those of Ni-Cu, Ni-P, and Cu-P, respectively. The Ni-incorporated Cu-P even has a much smaller Δ G_H* of -0.003 than that of Pt (∼-0.09 eV). We believe that our study will provide a new strategy to design non-noble metal alloy materials for practical applications in catalysis and energy fields.

Enhanced electrocatalytic hydrogen generation from water via cobalt-doped Cu2ZnSnS4 nanoparticles

Herein, we adopted a novel noble metal-free Co-doped CZTS-based electrocatalyst for the hydrogen evolution reaction (HER), which was fabricated using a facile, effective, and scalable strategy by employing a sonochemical method. The optimized Co-doped CZTS electrocatalyst shows a superior HER performance with a small overpotential of 200 and 298 mV at 2 and 10 mA-1, respectively, and Tafel slope of 73 mV dec-1, and also exhibits excellent stability up to 700 cycles with negligible loss of the cathodic current. The ease of synthesis and high activity of the Co-doped CZTS-based cost-effective catalytic system appear to be promising for HER catalysis.