Solvothermal synthesis of oxygen-incorporated MoS2-x nanosheets with abundant undercoordinated Mo for efficient hydrogen evolution

Activating the inert basal planes of layered molybdenum disulfide (MoS₂) is critical to deliver its high hydrogen evolution reaction (HER) efficiency. Herein, oxygen-incorparated MoS_x with abundant undercoordinated Mo atoms is fabricated by a facile solvothermal procedure, which realizes synergistically structural and electronic regulations of MoS₂ inert basal planes. Experiment results reveal that oxygen incoparation can effectively modulate the electronic structure and further optimize the intrinsic conductivity, while the defect-rich structure with abundant undercoordinated Mo atoms increases the number of active sites. Moreover, the influence of solvothermal temperature on activity of MoS_2-x is also investigated. The achieved MoS_x electrocatalyst prepared at 220 °C exhibits a superior activity for HER with a low overpotential of 191 mV at 10 mA cm⁻², a small Tafel slope of 67 mV dec⁻¹, and an excellent stability due to the largest surface area and superior conductivity.     

Self-supported three-dimensional WP2 (WP) nanosheet arrays for efficient electrocatalytic hydrogen evolution

The development of highly efficient, stable, eco-friendly and low-cost noble-metal-free electrocatalysts is still a great challenge to generate large scale hydrogen fuel from water. In this concern, self-supported WP₂ and WP nanosheet (NS) arrays were prepared through an in-situ solid-phase phosphidation of WO₃ nanosheet arrays on carbon cloth (CC), whereas, different phosphating temperatures of 650 °C, 800 °C for 2 h, has been utilized to attain different WP₂ NS/CC, WP NS/CC catalysts. Remarkably, the electrocatalysts of WP₂ and WP NS arrays exhibit an outstanding hydrogen evolution (HER) performance in acidic environment, with a low overpotential of 140 mV and 175 mV at 10 mA cm⁻², a Tafel slope of 85 mV dec⁻¹ and 103 mV dec⁻¹, respectively. Furthermore, Density Functional Theory (DFT) calculations reveal that the enhanced HER activity of WP₂ catalyst is attributed to the lowered hydrogen adsorption free energy on WP₂ surface, which is much lesser than that on the WP catalyst surface. As a result, WP₂ exhibit superior intrinsic catalytic activity than WP. This study offers a valuable way for the synthesis of highly efficient three-dimensional self-supporting catalytic electrodes, and beneficial for realizing the intrinsic electrocatalytic properties of tungsten phosphide for improved water splitting reactions.     

Influence of the phosphorus source on iron phosphide nanoparticle synthesis for hydrogen evolution reaction catalysis

Iron phosphide (FeP) is in the spotlight as a hydrogen evolution reaction (HER) catalyst due to its cost efficiency, good catalytic activity, and stability within a wide pH range. However, there is still a need to synthesize FeP nanoparticles (NPs) with systematic analysis to improve their catalytic activity. Herein, we report FeP NPs synthesized with various phosphorus sources (TOP, trioctylphosphine; TPP, triphenylphosphite; TEAP, tris(diethylamino)phosphine; and TBP, tri-n-butylphosphine) via phosphorization reaction. We clearly demonstrate that the HER activity of the catalyst based on the FeP phase is dependent on the choice of phosphorus source used in the colloidal NP synthesis. Among the samples, FeP NPs synthesized with TPP achieved the highest HER activity with an overpotential of 76 mV at 10 mA cm⁻² in 0.5 M H₂SO₄. Our results reveal a critical aspect of colloidal synthesis to achieve enhanced catalytic activity in the synthesis of transition metal phosphide NPs.     

Iron doped mesoporous cobalt phosphide with optimized electronic structure for enhanced hydrogen evolution

We report a self-supporting electrode fabricated by covering iron doped mesoporous cobalt phosphide film on carbon cloth substrate (meso-Fe_xCo_1-xP/CC) for hydrogen evolution reaction (HER). In acidic and alkaline electrolytes, the electrode exhibited excellent catalytic activity and fast kinetics towards the HER, only requiring small overpotentials of 61 mV and 67 mV to drive 10 mA cm^?2, respectively. The superior electrocatalytic activity is attributed to the mesoporous structure with high specific surface area (147.5 m² g^?1) and doping of Fe atom. The mesoporous structure grown on the conductive carbon cloth substrate enables the fully exposure of active sites and the rapid penetration of electrolyte. Additionally, density functional theory (DFT) calculation reveals that the doping of Fe enhances the adsorption of H atoms by shifting the d-band center of Co. Meanwhile, the introduction of Fe lowers the energy barrier for water dissociation, which accelerates the catalytic kinetics in alkaline electrolyte.     

Facile synthesis of carbon encapsulated RuO2 nanorods for supercapacitor and electrocatalytic hydrogen evolution reaction

In this work, carbon encapsulated RuO₂ nanorods (RuO₂ NRs/C) has been synthesized by thermolysis of ruthenium chloride and Punica granatum (P. granatum) peel under N₂ atmosphere. The synthesized RuO₂ NRs/C was characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction method (XRD), field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) with energy dispersive spectroscopy (EDS) analyses. The FT-IR results suggested that the organic constituents of P. granatum have been carbonized and encapsulated over RuO₂ nanorods (RuO₂ NRs). The XRD pattern of RuO₂ NRs/C revealed its crystalline nature and carbon encapsulation. The synthesized RuO₂ NRs/C has been well dispersed with the average width of 20 nm, exposed from the FE-SEM and HR-TEM images. The EDS results of RuO₂ NRs/C showed the existence of three elements viz., Ru, O and C. Further, the supercapacitor and electrocatalytic hydrogen evolution reaction (HER) activities of RuO₂ NRs/C were studied using standard electrochemical methods. The synthesized RuO₂ NRs/C offered a maximum specific capacitance of 151.3 F g⁻¹ at a scan rate of 5 mV s⁻¹, obtained from the cyclic voltammetry results. The onset over potential and Tafel slope of synthesized RuO₂ NRs/C for HER were −0.099 V_RHE and −99.4 mV dec⁻¹, respectively. The present study revealed that RuO₂ NRs/C as a better candidate for supercapacitor and HER.     

Phase transformation of iron phosphide nanoparticles for hydrogen evolution reaction electrocatalysis

Transition metal phosphides have emerged as alternative electrocatalysts for hydrogen evolution reaction (HER) due to their high activity and low cost compared to the conventional HER electrocatalysts such as Pt. However, the dependency of HER activity on different crystal phases is not well-understood. Here, we synthesized iron phosphide nanoparticles with two distinct phases via chemical transformation from iron metal to iron phosphides. During the development of iron phosphide phases by varying the synthesis conditions such as reaction temperature and time, the HER activities of the nanoparticle were examined. The HER activities of the iron phosphide nanoparticles were found to be phase-dependent.     

In-situ synthesis of porous Ni2P nanosheets for efficient and stable hydrogen evolution reaction

The design and development of highly efficient and stable non-noble metal electrocatalysts for hydrogen evolution reaction (HER) have attracted increasing attention. However, some key issues related to large overpotential, high cost and poor stability at high current density still remains challenging. In this work, we report a facile in-situ integration strategy of porous Ni₂P nanosheet catalysts on 3D Ni foam framework (PNi₂P/NF) for efficient and stable HER in alkaline medium. The two-step method can creates high density of ultra-thin porous Ni₂P nanosheets firmly rooted into Ni foam substrate which can guarantee excellent electrical contacts, strong substrate adherence and large amount of active sites. Such a binder-free flexible HER cathode exhibits superior electrocatalytic performance with an overpotential of 134 mV at current density of 10 mA cm⁻². It also shows superior stability at higher current densities of 100 and 500 mA cm⁻² for at least 48 h and negligible performance degradation is observed.     

NiCoP nanoarchitectures: One-step controlled electrodeposition and their application as efficient electrocatalysts for boosting hydrogen evolution reaction

Designing non-precious and long-lasting electrocatalysts with enhanced catalytic properties for hydrogen evolution reaction (HER) is a fundamental approach to address the needs for hydrogen industry and overcome the current challenges in sustainable energy generation. Herein, we present ternary NiCoP nanostructures synthesized through a direct and controlled electrochemical deposition at room temperature as highly efficient electrocatalysts for HER. Different Ni/Co ratios in the alloy were investigated resulting in different nanoarchitectured morphologies, chemical compositions and HER performances, in turn. The NiCoP–I alloy exhibited a nanoparticulated morphology comprising well-defined nanoparticles of ～20–30 nm which evolved to nanoparticulated caps at prolonged electrodeposition times presenting a large electrochemical surface area of 526 cm². The NiCoP–I electrocatalyst demonstrated a small Tafel slope of 49 mV dec^?1 and an ultra-low overpotential of 68 mV vs. RHE at ?10 mA cm^?2 in alkaline solution which well rivals to that of Pt foil and outmatches its binary alloy counterparts.     

Metal and phosphonium-based ionic liquid: A new Co and P dual-source for synthesis of cobalt phosphide toward hydrogen evolution reaction

Phosphonium-based ionic liquid, containing cobalt ion, was applied as novel phosphorus and metal dual-source for fabrication of cobalt phosphide. Trihexyl(tetradecyl)phosphonium tetrachlorocobaltate(II) ([P_6,6,6,14]₂[CoCl₄]) with carbon nanotubes (CNTs) was utilized to obtain the Co₂P/CNTs via one step phosphidation. This material exhibits a good catalytic activity toward hydrogen evolution reaction (HER) including an onset overpotential of 85 mV, a Tafel slope of 47 mV dec⁻¹, current densities of 10 and 20 mA cm⁻² at overpotentials of 150 and 178 mV, and it has a good stability to keep the HER activity. All experimental results confirmed that [P_6,6,6,14]₂[CoCl₄] can form Co₂P without adding other reagent and CNTs can improve the electrical conductivity and contribute to the formation of cobalt phosphide.     

Controllable synthesized CoP-MP (M=Fe,Mn) as efficient and stable electrocatalyst for hydrogen evolution reaction at all pH values

The introduction of metal atom or heteroatom into transition metal phosphide is an effective strategy to enhance the electrochemical activity for hydrogen evolution reaction, while the controllable synthesis and purposeful design of efficient and stable transition metal phosphide based electrocatalyst with typical structural morphology is still a big challenge. Here, we investigated the relationship among the variety of the doped metal element (Fe and Mn), the corresponding morphology and electrocatalytic performance of the obtained sample for hydrogen evolution reaction. We found that with the doping of Fe and Mn, the cylinder-like CoP has transformed into microflower-like CoP-FeP and rambutan-like CoP-MnP, respectively. Meanwhile, the obtained CoP-FeP exhibits the excellent electrocatalytic activity hydrogen evolution reaction (HER) over a wide pH range (0–14), followed by CoP-MnP and CoP, resulting from the typical nanostructure and the moderately optimized electronic structure of P and Co center.     

Facile synthesis of NiS2 nanowires and its efficient electrocatalytic performance for hydrogen evolution reaction

Recently, the first-row transition metal dichalcogenides MX₂ (M = Fe, Co, Ni; X = S, Se) have been widely reported as promising catalysts for hydrogen evolution reaction (HER) because of its excellent catalytic activity and earth-abundance. The rational nanostructure designs have been proved as an effective way to improve their catalytic performance. However, the reported one dimension (1D) NiS₂ nanowires for HER suffer from a large Tafel slope. Here, we report a facile synthesis of 1D NiS₂ nanowires and its high efficient catalytic activity in HER. This nanowire structure with large surface area and active sites enables highly efficient electrocatalytic performance in HER with a much smaller Tafel slope (83.5 mV/dec) compared to that of bulk NiS₂ (136 mV/dec) as well as long-term stability. Our work builds up a structure–performance relationship and enriches the synthetic strategy to other efficient catalysts such as first-row transition metal dichalcogenides or transition metal phosphide.     

Heterostructured CoP/MoO2 as high efficient electrocatalysts for hydrogen evolution reaction over all pH values

Delicate design and rapid development of low-cost, highly active, and perdurable pH-universal heterogenveous hydrogen evolution reaction (HER) electrocatalysts are demanding challenge in energy-conversion technologies. Herein, heterostructured CoP/MoO₂ electrocatalyst was synthesized by employing MoO₂ nanorods as framework for the growth of CoP nanoparticles. Owing to the fact that the effective interface of heterostructure can enhance electron transfer/mass diffusion and expose ample active sites, the CoP/MoO₂ reveals eminent HER activities with favorable long-term stability in all pH electrolytes, overpotentials of 69, 78, and 165 mV in 0.5 M H₂SO₄, 1.0 M KOH, and 1.0 M PBS (phosphate-buffered solution) electrolytes were required for CoP/MoO₂ to reach the current density of 10 mA cm^?2. This work emphasizes that strategy of electronic structure engineering holds great promises in pH-universal HER electrocatalysts for energy storage and conversion.     

3D self-standing grass-like cobalt phosphide vesicles-decorated nanocones grown on Ni-foam as an efficient electrocatalyst for hydrogen evolution reaction

The growing hydrogen consumption has greatly promoted the development of efficient, stable and low-cost electrocatalysts for the hydrogen evolution reaction (HER). Constructing functional nanostructures is an efficacious strategy to optimize catalytic performance. Herein, we present a feasible route to fabricate distinctive 3D grass-like cobalt phosphide nanocones clad with mini-vesicles on the hierarchically porous Ni foam, which can directly serve as a binder-free electrocatalyst with superior catalytic activity and durability in HER. Thanks to its distinctive 3D microstructure featured with favourable pore-size distribution, abundant active sites provided by mini-vesicles and rapid electron transfer with the assistance of Ni foam, the as-grown grass-like CoP/NF electrocatalyst has shown a favourable overpotential in an acidic solution with an onset overpotential of ∼35 mV, an overpotential of 71 mV at a current density of 10 mA cm⁻², reduced by 60 mV in comparison with that realized by urchin-like CoP/NF nanoprickles. Moreover, it has exhibited an excellent HER activity in the alkaline medium, with an overpotential of 117 mV at 10 mA cm⁻², a Tafel slope of 63.0 mV dec⁻¹ and a long-term electrochemical durability.     

Facile synthesis of tubular CoP as a high efficient electrocatalyst for pH-universal hydrogen evolution

A facile three-step approach for tubular CoP preparation and its catalytic activity for HER and OER are reported. The CoP microtubes show superior HER performance in a wide pH range with low overpotentials of 91, 101 and 113 mV at 10 mA cm^?2 in 0.5 M H₂SO₄, 1 M KOH and 1 M PBS, respectively. Additionally, it also depicts superior OER performance with an overpotential of 300 mV at 10 mA cm^?2, which is lower than reported precious metal oxides. The improved electrocatalytic performance of tubular CoP is likely attributed to the porous tube-like structural features, which not only afford rich exposed active sites, but also accelerate the charge or mass transfer efficiency, and thus efficiently promote the HER performance. The synthesis of tubular CoP confirms the importance of morphology features and provides a new insight to rationally design and synthesize highly effective non-noble metal phosphide-based pH-universal electrocatalysts for HER.     

Facile synthesis of self-supported intertwined columnar NiCoP as a high efficient electrocatalyst for hydrogen evolution reaction

A new self-supported nickel-cobalt phosphide (NiCoP) on Ni foam (NiCoP/NF) is fabricated by simple immersion in Co(NO₃)₂ solution followed by subsequent phosphorization. NiCoP/NF displays intertwined and porous columnar morphology derived from topological transformation of corresponding columnar amorphous hydroxides precursor. NiCoP/NF manifests the most prominent hydrogen evolution reaction (HER) performance in both 0.5 M H₂SO₄ and 1 M KOH with the overpotentials of 49 and 57 mV to achieve 10 mA cm^?2, respectively. Also, NiCoP/NF showed excellent oxygen evolution reaction (OER) performance, requiring 256 mV to achieve 10 mA cm^?2, even superior to that of RuO₂ and IrO₂. Such impressive HER performance of NiCoP/NF is mainly attributed to the collective effects of enlarged surface area and enriched exposed active sites, affording faster charge transfer kinetic in HER process. This simple immersion method offers a new insight to design cost-effective and efficient electrocatalysts for large scale application.     

Flower-like MoS2 with stepped edge structure efficient for electrocatalysis of hydrogen and oxygen evolution

A flower-like MoS₂ with a stepped edge structure was successfully and controllably fabricated as a bifunctional electrocatalyst efficient for hydrogen and oxygen evolution reactions. The hierarchically porous polycrystalline MoS₂ was characterized by a combination analysis of XRD, Raman, XPS, N₂-BET, SEM and TEM. In the hydrogen evolution reaction (HER), this as-obtained MoS₂/Ni catalyst presents significantly enhanced performance versus most previously studied catalysts. In the oxygen evolution reaction (OER), the electrocatalyst MoS₂/Ni gives rise to a rather low overpotential of ∼0.335 V at 20.0 mA cm⁻² and much enhanced durability over 6 h.     

Hierarchical MoS2 nanosheets integrated Ti3C2 MXenes for electrocatalytic hydrogen evolution

In this study, conductive Ti₃C₂ MXenes were used as a promoter to accelerate charger transfer of MoS₂, realizing highly efficient HER electrocatalysis. A facile hydrothermal strategy is demonstrated to be effective for in situ growth of MoS₂ nanosheets vertically standing on planar Ti₃C₂ nanosheets to form hierarchical heterostructures. Beneficial from the opened layer structures and strong interfacial coupling effect, the resulting MoS₂/Ti₃C₂ heterostructures achieve a giant enhancement in HER activity compared with pristine MoS₂ nanosheets. More specifically, the catalytic current density induced by MoS₂/Ti₃C₂ heterostructures at an overpotential of ∼400 mV is nearly 6.2 times as high as that of the pristine MoS₂ nanosheets. This work uncovers that the Ti₃C₂ nanosheets are ideal candidates for construction of highly active electrocatalysts for water splitting.     

Rod-like nonstoichiometric Ni0.85Se as efficient electrocatalysts for hydrogen evolution reaction

Nickel selenides with different Ni/Se atomic ratio have been successfully synthesized by a simple solvothermal method. Among them, the nonstoichiometric compound (Ni_0.85Se) (A-10) behaved excellent electrochemical catalytic activity towards hydrogen evolution reaction. Furthermore, it presents an ultra-low overpotential (η) of 190 mV and extremely small Tafel slope of 57 mV/dec when the current density j_A reaches ～10 mA/cm². At the same time, it has large effective electrochemical active surface area and shows outstanding stability after a long time chronoamperometry testing.     

Tuning of electrocatalytic activity of mixed metal dichalcogenides supported NiMoP coatings for alkaline hydrogen evolution reaction

The mixed metal dichalcogenides combination of WS₂–MoS₂ was coated onto Cu substrate by electroless NiMoP plating technique and the electrocatalytic hydrogen evolution reaction (HER) performance was investigated. The enhanced structural, morphological parameters and boosted electrocatalytic performance of the various metal-metal molar ratio of WS₂–MoS₂ onto NiMoP plate were identified under variable operating conditions and it was successfully evaluated by various characterization techniques. The well-defined crystalline nature, phase, particle size, structure, elemental analysis and surface morphology of prepared coatings were analyzed by FESEM, XRD, AFM and EDS mapping. The electrochemical analysis was performed using open circuit potential (OCP) analysis, chronoamperometry (CA), electrochemical impedance spectroscopy (EIS), Tafel curves, linear sweep voltammetry (LSV), cyclic voltammetry (CV) and polarization studies to find the activity of prepared electrocatalyst towards electrochemical hydrogen evolution reactions. The performance of bare NiMoP and WS₂–MoS₂/NiMoP plates were compared and found that the HER activity of NiMoP can be reinforced by composite incorporation through the synergic effect arises with in the catalytic system, which improves surface roughness and enhances the magnitude of electrocatalyst toward HER. The achievement of enhanced catalytic performance of coatings was authenticate by the kinetic parameters such as decreases in Tafel slope (98 mV dec^?1), enhanced exchange current densities (9.32 × 10^?4 A cm^?2), and a lower overpotential. The consistent performance and durability of the catalyst were also investigated. The enhanced electrocatalytic activity of WS₂–MoS₂/NiMoP coatings increased with respect to the surface-active sites associated with combination of mixed dichalcogenides and the synergic effect arises in between different components present in the coating system. This work envisages the progressive strategies for the economical exploration of a novel WS₂–MoS₂/NiMoP water splitting catalyst used for large scale H₂ generation. The prepared WS₂–MoS₂/NiMoP embedded Cu substrate possess high catalytic activity due to its least overpotential of 101 mV at a benchmark current density of 10 mA cm^?2, which demonstrated the sustainable, efficient and promising electrocatalytic property of prepared catalyst towards HER under alkaline conditions.