Molybdenum Phosphide Nanoparticles Research Articles

Molybdenum phosphide nanoparticles encapsulated with biomolecule-derived N, P-codoped carbon nanosheets for the synergistic hydrogen evolution reaction

A one-step pyrolysis strategy to synthesize novel MoP nanoparticles encapsulated with biomolecule-derived N, P-codoped carbon nanosheets for synergistic hydrogen evolution reaction.

Theoretical insights of electrocatalytic hydrogen evolution on MoP nanocrystal

A methodical computational investigation was performed to gain insights into the factors and mechanisms that determine the catalytic activity of molybdenum phosphide (MoP). We analysed the structure and energetics as well as hydrogen adsorption behaviour on the (100) crystallographic plane of MoP. The Gibbs free energy and density of states studies were performed to elucidate the crystal chemistry and bonding mechanism of MoP(100) with the adsorbate. The computed values of ΔGH∗ at different hydrogen coverages are then used to predict the hydrogen evolution reaction (HER) activity on the (100) surface. The obtained values of hydrogen Gibbs free energy of adsorption ΔGH showed HER activity ranging between −0.35 and 0.10 eV. Our study has placed the (100) surface of MoP nanoparticles as highly suited analogues to platinum in the HER. The high intrinsic activity of MoP(100) is a result of a distinct electronic structure induced by the presence of phosphorus a phenomenon known as a ‘ligand effect’. The presence of phosphorus benefits the catalyst by improving intrinsic catalytic activity and enhancing proton adsorption kinetics. The results obtained from this study proved that phosphorizing and surface faceting play a crucial role in enhancing the catalytic performance of transition metals. Key trends that underpin the potential of MoP(100) as a catalyst for improved HER were identified, with a view to implement these findings for the practical design of improved catalysts for hydrogen production based on molybdenum phosphide.

Metal-organic framework-derived molybdenum phosphide@mesoporous carbon composite for electrochemical acetaminophen detection

Electrochemical methods have attracted great attention in the detection of acetaminophen (AP) due to their high sensitivity, rapidity, and simplicity. Molybdenum phosphide (MoP) with excellent catalytic activity and redox property has been widely used for electrochemical applications. In this work, MoP nanoparticles loaded with mesoporous carbon (MoP@C-D2) were successfully synthesized and characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) method, and X-ray photoelectron spectroscopy (XPS). It is shown that the temperature rising process and the amount of polyoxometalate and NaH2PO2 can significantly affect the specific surface areas and pore structures of the product, thereby affecting their sensing performances. Structural studies indicated that MoP nanoparticles in MoP@C-D2 were uniformly dispersed in mesoporous carbon matrix, endowing the composite high conductivity, large specific surface area, and good catalytic activity. MoP@C-D2 modified electrode showed a wide linear detection range of 1.24–1071.4 μM, the detection of limit (LOD) of 0.008 μM, high stability, and good selectivity for AP detection. In addition, the constructed electrode can also be used to detect the content of AP in commercial medicine. This work extends the application of mesoporous MoP-based composite in electrochemical sensing.

Ultrafine cobalt molybdenum phosphide nanoparticles embedded in crosslinked nitrogen-doped carbon nanofiber as efficient bifunctional catalyst for overall water splitting

As a kind of high-performance and cost-efficient electrocatalyst in water splitting, the transition bimetal phosphides exhibit a promising prospect. Here, the composite of cobalt molybdenum phosphide nanoparticles embedded in crosslinked nitrogen-doped carbon nanofiber (Co0.4Mo0.6P@CL-NCNF) has been synthesized via an electrospinning process and pyrolysis treatment. As an effective hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalyst, the Co0.4Mo0.6P@CL-NCNF only requires the overpotentials of 81 mV and 219 mV at the current densities of 10 mA cm−2 and 20 mA cm−2, respectively. Moreover, the water electrolyzer with the Co0.4Mo0.6P@CL-NCNF as the cathode and anode catalysts requires a cell voltage of 1.59 V to reach a current density of 10 mA cm−2. The Co0.4Mo0.6P@CL-NCNF also achieves the excellent stability up to 24 h for HER, OER and overall water spitting in 1.0 M KOH. The excellent catalytic activity of the Co0.4Mo0.6P@CL-NCNF is benefits from the synergistic effect between components and the crosslinked structure of carbon nanofiber. Thus, the research provides a promising method for preparing carbon-based TMPs materials towards electrocatalysis.

Interfacial interaction between molybdenum phosphide and N, P co-doped hollow carbon fibers boosting the oxygen electrode reactions in zinc-air batteries

The development of highly efficient electrocatalysts with excellent stability and electrocatalytic activity for oxygen electrode reactions is important for facilitating the application of rechargeable zinc-air batteries. The interface interaction between components is one of the most important factors that affects the catalytic activity of electrode materials. Herein, N and P co-doped hollow carbon fibers embedded with molybdenum phosphide nanoparticles (MoP@N, P-HCF) are elaborately fabricated as novel bifunctional electrocatalysts to study the influence of interface interaction on oxygen redox reactions in zinc-air batteries. As evidenced, a strong electron transfer is realized at the interface between N, P-HCF and MoP NPs due to their remarkable interfacial interaction, enabling the uniform combination of the nanoparticles with the doped carbonaceous matrix. More importantly, the rearrangement of electrons along the heterogeneous interface in MoP@N, P-HCF endows the electrode with abundant active sites and excellent catalytic activity, thus promoting the kinetics of the oxygen electrode reactions. Based on the above merits, MoP@N, P-HCF based rechargeable zinc-air batteries demonstrate improved power density of 93.8 mW cm−2 and superior cyclability of over 600 cycles. Our work emphasizes the significant role of interface chemistry between conductive carbon matrix and transition metal compounds in regulating the catalytic activity and provides a profound insight for the development of highly active and stable oxygen electrode materials.

Electron density modulation of MoP by rare earth metal as highly efficient electrocatalysts for pH-universal hydrogen evolution reaction

Profiting from Pt-like electronic structure and high electrical conductivity, molybdenum phosphide (MoP) has received widespread attention as a hydrogen evolution reaction (HER) catalyst. Although various effective strategies have been developed to regulate the bare MoP synthesis, the electrocatalytic performance of MoP is still far from satisfactory, especially in pH-universal applications. Recently, doping of heterogeneous elements, particularly for rare earth (RE) metals, has been emerged as an effective method to precisely regulate the local electronic structure of phosphides. Herein, the novel and controllable La/Yb-doped MoP nanoparticles encapsulated in nitrogen-doped carbon matrix (MoP@NC) are synthesized. The as-prepared La/Yb-doped catalysts (RE-MoP@NC (RE = La, Yb)) exhibit fantastic HER electrocatalytic performance for both activity and durability in a wide pH range. Detailed structural characterizations and density functional theory (DFT) calculations validate that the electronic densities around Mo and P atoms are effectively tuned by La/Yb doping atoms, resulting in the optimization in Gibbs free energy of MoP toward the hydrogen adsorption, which can boost its intrinsic HER activity. This research enriches RE-modified catalysts and reveals that the RE metal doping can be extended to other non-noble metal catalysts as a general method.

Molybdenum phosphide coupled with highly dispersed nickel confined in porous carbon nanofibers for enhanced photocatalytic CO2 reduction

Photoreduction of CO2 to chemical fuels offers a promising strategy for managing the global carbon balance using renewable solar energy. However, the decisive process of oriented photogenerated electron delivery presents a considerable challenge. The performance of most transition metal compounds, as photocatalysts for CO2 reduction, is largely limited by their inherent stacked structure, poor conductivity, and fast recombination of photogenerated electron-hole pairs. Herein, we report the construction of porous nitrogen-doped carbon nanofibers (NCPF) with highly dispersed Ni and molybdenum phosphide nanoparticles (Ni-MoP@NCPF) loaded for photocatalytic CO2 reduction. The porous carbon nanofibers with high conductivity and open ends can effectively promote charge/mass transfer and improve CO2 adsorption. The loaded Ni species exist at a highly dispersed state that are stabilized by formation of coordinating Ni-N bonds with N from pyrrolic nitrogen in NCPF. The incorporation of Ni and its electronic coupling with MoP can adjust the band structure of the resultant material and alter the transfer route of the photogenerated carriers. The Ni-MoP@NCPF exhibits a CO product selectivity up to 98.95% with a rate of 953.33 μmol g−1h−1 under visible light irradiation, which is 9.37 times faster than that of Ni-free MoP@NCPF. These findings provide new insights into photocatalytic CO2 reduction on cost-effective transition metal compounds through combined morphology, composition, and heterointerface engineering.

Three-dimensional nano/micro-structured porous MoP/CNTs microspheres as high-capacity anode for lithium-ion batteries

Molybdenum phosphide (MoP) is considered one of the promising electro-active materials for lithium-ion batteries (LIBs) owing to the high theoretical capacity but development of MoP anodes faces challenges such as the poor cycle stability. Herein, we propose a facile strategy to synthesize MoP/CNTs microspheres from a spray drying method followed by a phosphating process. The carbon nanotubes (CNTs) are inlaid throughout the MoP/CNTs microspheres, which not only promotes the electrical conductivity of the composite, but also relieves volume change during cycling. Benefit from the synergistic effect by coupling the MoP nanoparticles with CNTs and the nano/micro structure, the anode material of porous MoP/CNTs microspheres shows excellent cycling stability and specific capacity, for example, a capacity of 1568 mAh g−1 for 300 cycles at 200 mA g−1. Quantitative kinetics analysis reveals that the charge storage mechanism of MoP/CNTs mainly relies on pseudocapacitance behavior, especially at high scan rates (86.6% at 0.5 mV s−1), which improves the lithium storage performance at high scan rates. Our results provide insights into the design and synthesis of the functional materials with nano-micro structure for high-performance LIBs.

Wide pH range electrocatalytic hydrogen evolution using molybdenum phosphide nanoparticles uniformly anchored on porous carbon cloth

The development of efficient and inexpensive electrocatalysts is regarded as an urgent concern in electrochemical water-splitting system. Herein, we propose a novel strategy for the fabrication of molybdenum phosphide nanoparticles (MoP NPs) anchored on porous carbon cloth (MoP@PCC) as a noble metal–free electrocatalyst for hydrogen evolution reaction (HER). Benefiting from the thin and uniform coating of ultrafine molybdenum dioxide (MoO2) NPs on PCC, less-aggregated MoP NPs can be formed on PCC after thermal phosphidation, resulting in an efficient performance for HER over a wide pH range. Particularly, MoP@PCC exhibited good electrocatalytic activities in alkaline and neutral solutions with low overpotentials of 122 and 160 mV at a current density of −10 mA cm−2, respectively. Additionally, MoP@PCC exhibited long-term stability and durability with continuous 10,000 cyclic voltammetry (CV) cycles and chronopotentiometric operation over 50 h, both in alkaline and neutral solutions.

Template-free fabrication of MoP nanoparticles encapsulated in N-doped hollow carbon spheres for efficient alkaline hydrogen evolution

Based on the synergy between MoP and N-doped carbon, MoP nanoparticles encapsulated in N-doped carbon hollow spheres were synthesized using inorganic-organic hybrids as precursors, which shows an excellent stability and activity with an overpotential 96 mV at 10 mA cm −2 and a small Tafel slope of 53 mV dec −1 in alkaline solution. • A template-free approach was developed to fabricate MoP@NC hollow microsphere. • Inorganic-organic hybrids were used as precursors. • Remarkable electrocatalytic hydrogen evolution performance could be achieved. • The synergy between MoP and the pyridinic N could optimize the electronic structure. Encapsulating transition metal phosphides into nitrogen-doped carbon (NC) materials is an effective strategy to enhance the electrocatalytic performance. Herein, we develop a novel template-free approach to rationally fabricate molybdenum phosphide (MoP) nanoparticles encapsulated in N-doped carbon (MoP@NC) hollow microspheres for alkaline hydrogen evolution reaction (HER) by employing inorganic-organic hybrids as precursors, in which phosphorus source of the MoP@NC derives from tetra (hydroxymethyl) phosphorus chloride for the first time. The optimized MoP@NC sample shows a low overpotential of 96 mV at 10 mA cm −2 , a small Tafel slope of 53 mV dec −1 , and excellent stability. The enhanced HER performance is mainly attributed to the integrated effects of a distinctive hollow structure, high pyridinic N-doping level, and the extremely intimate synergy between MoP and NC. Theoretical calculations indicate that the active sites of the catalyst are mainly located at Mo atoms adjacent to the pyridinic N-doped carbon layer (pyridinic-N-MoP); the synergistic interaction between MoP and pyridinic N (rather than pyrrolic or graphitic N) atoms can lower the d band center of Mo, weaken the Mo-H ads bond and thereby enhance HER performance. In addition, the pyridinic N atoms at the interactive sites play a key role in adsorbing H 2 O and preventing the adsorption of OH*, resulting in accelerating the water splitting. This work provides a new method to rationally synthesize high-efficient and stable MoP-based hollow sphere electrocatalysts for alkaline HER through designing inorganic-organic hybrid precursors.

In-situ Synthesis of Coral-Like Molybdenum Phosphide (MoP) Microspheres for Lithium-Ion Battery

Molybdenum phosphide (MoP) has attracted extensive attention as promising anode candidates for lithium-ion batteries owing to its high specific capacity, low potential range and low polarization. However, severe volume changes and intrinsic low conductivity are major challenges for further application of MoP electrode materials. In this work, a coral-like MoP microsphere encapsulated by N-doped carbon (MoP@NDC) was successfully prepared through annealing the precursor derived from self-polymerization of dopamine with phosphomolybdic acid. The introduction of carbon framework not only serves as matrix to confine MoP nanocrystals from aggregations, but also improves the electrochemical conductivity and facilitates lithium ion or electron transport on the surface of MoP. Such hierarchical structure delivered high discharge capacity of 495 mAh g−1 after 300 cycles with 90.1% capacity retention, which could be attributed to the synergistic effects of MoP nanoparticles and conductive carbon network. This design strategy shows MoP@NDC electrode with applicable application as anode in lithium-ion battery.

Colloidal synthetic methods of amorphous molybdenum phosphide nanoparticles for hydrogen evolution reaction catalysts

Transition metal phosphides (TMPs) have recently emerged as promising hydrogen evolution reaction (HER) catalytic alternatives to platinum. Among them, molybdenum phosphide (MoP) has attracted extensive attention due to its high electrical conductivity, good stability, and Pt-like electronic structure; however, there is no systematic comparison of its different colloidal synthetic routes. This study systematically compares two colloidal synthetic methods, one-pot and two-step, for amorphous MoP and the associated morphological changes during their reaction time. The amorphous MoP nanoparticles synthesized via the two-step method within 4 h exhibited the highest HER performance with an overpotential of 177 mV in 0.50 M H2SO4 for a current density of −10 mA cm−2; this might be due to their highly developed Mo-P bondings revealed by X-ray photoelectron spectroscopy analysis. Thus, this work demonstrates that the HER catalytic performance of MoP can be significantly influenced by its synthetic method and reaction time.

MoP nanoparticles encapsulated in P-doped carbon as an efficient electrocatalyst for the hydrogen evolution reaction

Numerous efforts have been made to search for high-efficiency and noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER). In this work, molybdenum phosphide (MoP) nanoparticles encapsulated in P-doped carbon (MoP@PC) was synthesized through a facile one-step pyrolysis of the precursor, namely 3D cross-linked network structure of MoOx contained in polyaniline and phytic acid (MoOx@PANI-PA). The obtained MoP@PCelectrocatalyst retained the 3D structure and exhibits outstanding HER abilities with ultra-low overpotential (η10 = 69 mV), small Tafel slope (55 mV dec−1) and high stability in acid solution. This work offers a facile method to prepare cost-effective transition metal phosphide catalysts.

Phytic acid-derived fabrication of ultra-small MoP nanoparticles for efficient CO methanation: Effects of P/Mo ratios

Molybdenum phosphide (MoP) catalyst has been widely applied in hydrogenation reactions, while the preparation of unsupported MoP catalysts with ultra-small size and large specific surface area (SBET) is still challenging. Herein, we have provided a facile method for preparing a series of MoP-x (x = P/Mo ratios ranging from 1 to 5) catalysts by pyrolyzing phytic acid (PA)-derived Mo complexes in a H2 atmosphere. The physicochemical properties and the catalytic activity of MoP catalysts were investigated. The results showed that the obtained MoP-5 catalyst had the largest SBET and exhibited ultra-small nanoparticle diameter of 3.6 nm, which ascribed to the chelation of PA and the confinement of deposited products. As the content of PA increased, the synthetic mechanism of MoP was also affected, which led to the difference in the valence of surface Mo species. The characterization results further confirmed that Moδ+ sites in MoP catalysts are active sites for methanation reaction and its content on the surface of MoP-x catalysts determines the catalytic activity.

Preparation of molybdenum phosphide nanoparticles/nitrogen-phosphorus co-doped carbon nanosheet composites for efficient hydrogen evolution reaction

The molybdenum phosphide (MoP) nanoparticles supported by phosphorus and nitrogen co-doped carbon nanosheet (N, P–C) have been prepared through simple one-step calcination method. The composition and morphology of the prepared hybrids were further characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and so on. The characterization results prove that the annealing temperature plays an essential role in the fabrication of nanosheets morphology. All characterization results prove that the MoP nanoparticles were uniformly loaded on N,P–C nanosheets. As excepted, the unique nanosheet structure not only contributes to mass transfer and electron transfer, but also increases electrochemical surface area. The obtained MoP/N,P–C-900 composites exhibit excellent HER activity and long-time stability (η ​= ​129 ​mV for reaching 10 ​mA ​cm−2 and 10 ​h for successive testing), which is superior than many other non-precious metal electrocatalysts. The present work affords a promising strategy for designing novel HER electrocatalysts, which may be applied in storage systems and diverse energy conversion.

Hierarchical ultrathin carbon encapsulating transition metal doped MoP electrocatalysts for efficient and pH-universal hydrogen evolution reaction

Molybdenum phosphide (MoP) has been recognized as a promising family of non-noble metal electrocatalysts for hydrogen evolution reaction (HER) by water splitting, but their electrocatalytic HER activities are still far from desirable and the active sites of MoP-based electrocatalysts have rarely been explored. Herein, we demonstrate a novel hybrid nanostructure composed of carbon encapsulating ultra-low Co/Ni-doped MoP nanoparticles, which can be adopted as highly active and stable HER catalysts in pH-universal electrolytes. The optimized carbon-encapsulated MoP nanoparticles with a Ni/Mo molar ratio of 0.02 achieve a low overpotential of 102 mV at 10 mA cm−2 and a small Tafel slope of 58.1 mV dec−1 in 0.5 M H2SO4 solution, outperforming most of previously reported MoP-based electrocatalysts. More importantly, density functional theory based calculations reveal that the △GH* of Ni/Co doped MoP at the Mo site is lower than that at the P site, and the lowest △GH* of the doping form of Ni and Co at Mo site was interstitial and substitutional + interstitial, respectively. Higher catalytic performance is observed on doped Mo-terminated surface especially in the presence of non-stoichiometric Ni and Co defects. The lowest free energy of Ni-doping implies that Ni-doped MoP hybrid nanostructures possess weak hydrogen adsorption energy and excellent HER catalytic activity in a wide pH range. The combined experimental and theoretical study paves the way for the identification of the active sites in MoP-based hybrid electrocatalysts toward high-performance HER.

Hierarchical molybdenum phosphide coupled with carbon as a whole pH-range electrocatalyst for hydrogen evolution reaction

In the effort to develope more effective electrocataysts for water electrolysis hydrogen generation through hydrogen evolution reaction (HER), the well-crystallized molybdenum phosphide nanoparticles dispersed in three-dimensional N,P-codoped graphite carbon nanosheets (3D MoP/NPG) are synthesized in this work using a SiO2-template-assisted strategy. Instrument characterization shows that the catalyst has a large specific surface area, high electrical conductivity, and the coupled interfaces & synergistic effect between MoP and carbon sheets toward electrocatalytic HER. Experimental results reveal that MoP/NPG possesses remarkable catalytic HER activity and stability in a wide pH range. Density functional theory (DFT) calculations reveal that the coupled interaction between MoP and carbon sheet interfaces can induce an optimal free energy of hydrogen adsorption on the catalyst surface. Both the theoretical calculations and experimental results demonstrate that the hierarchical structure with synergistic interaction between MoP and carbon sheets can facilitate charge transfer kinetics to enhance HER performance.

NaCl template-directed approach to ultrathin lamellar molybdenum phosphide-carbon hybrids for efficient hydrogen production

Molybdenum phosphide (MoP) is a prospective non-precious catalyst for hydrogen evolution reaction (HER), though its HER elctrocatalytic performance need to be further enhanced. We first report a facile, easy-scalable and low-cost approach for fabricating porous lamellar MoP/C hybrids by simply mixing the common ingredients of ammonium molybdate, ammonium dihydrogen phosphate, dicyandiamide and sodium chloride (NaCl), followed by freeze-drying, annealing and water-washing. Here, NaCl is used as pore-forming and template-directing agent during the high-temperature annealing and “cooling recrystallization” process. Highly crystalline and ultrafine MoP nanoparticles are intimately wrapped by lamellar carbon nanosheets. The lamellar conductive architecture with ultrathin and porous carbon nanosheets provides multiple attractive properties for HER, such as impeding the growth of nanoparticles, offering an expressway for boosting mass/charge transfer, and delivering large specific surface area with numerous exposed eletrocatalytic sites. Consequently, the MoP/C (NaCl) electrocatalyst presents a low HER overpotential of 118 mV at 10 mA cm−2 with a small Tafel slope of 50.7 mV dec−1 in 0.5 M H2SO4, as well as robust stability. Moreover, a home-made electrolyzer using MoP/C (NaCl) as cathode achieves 0.71 A cm−2 at 2 Vcell at 80 °C, and is operated stably for more than 3300 min at 150 mA cm−2.

Defective crystalline molybdenum phosphides as bifunctional catalysts for hydrogen evolution and hydrazine oxidation reactions during water splitting

Defect-rich crystalline molybdenum phosphide nanoparticles anchored on reduced graphene oxide serve as an efficient bifunctional electrocatalyst for both hydrogen evolution and hydrazine oxidation reactions.

Direct synthesis of parallel doped N-MoP/N-CNT as highly active hydrogen evolution reaction catalyst

Doped phosphide is promising in earth-abundant element based catalysts for hydrogen evolution reaction (HER). Here we employ ammonium hypophosphite (NH4H2PO2) to synthesize a novel parallel doped catalyst, nitrogen doped molybdenum phosphide nanoparticles (NPs) supported on nitrogen doped carbon nanotubes (N-MoP/ N-CNTs ). The NH4H2PO2 as a bifunctional agent severs as both phosphidation agent and nitrogen source, which makes the synthetic route simple and efficient. The as-obtained parallel doped N-MoP/N-CNTs show an overpotential of 103±5 mV at 10 mA cm−2, which is 140 mV lower than that of MoP NPs. The enhanced HER performance is attributed to the electronic effect by doped MoP and CNTs supports. This work provides a facile route to synthesize doped phosphides for the potential applications in hydrogen energy.