Trimetallic Mn‐Fe‐Ni Oxide Nanoparticles Supported on Multi‐Walled Carbon Nanotubes as High‐Performance Bifunctional ORR/OER Electrocatalyst in Alkaline Media

Discovering precious metal‐free electrocatalysts exhibiting high activity and stability toward both the oxygen reduction (ORR) and the oxygen evolution (OER) reactions remains one of the main challenges for the development of reversible oxygen electrodes in rechargeable metal–air batteries and reversible electrolyzer/fuel cell systems. Herein, a highly active OER catalyst, Fe_0.3Ni_0.7O_X supported on oxygen‐functionalized multi‐walled carbon nanotubes, is substantially activated into a bifunctional ORR/OER catalyst by means of additional incorporation of MnO_X. The carbon nanotube‐supported trimetallic (Mn‐Ni‐Fe) oxide catalyst achieves remarkably low ORR and OER overpotentials with a low reversible ORR/OER overvoltage of only 0.73 V, as well as selective reduction of O₂ predominantly to OH^?. It is shown by means of rotating disk electrode and rotating ring disk electrode voltammetry that the combination of earth‐abundant transition metal oxides leads to strong synergistic interactions modulating catalytic activity. The applicability of the prepared catalyst for reversible ORR/OER electrocatalysis is evaluated by means of a four‐electrode configuration cell assembly comprising an integrated two‐layer bifunctional ORR/OER electrode system with the individual layers dedicated for the ORR and the OER to prevent deactivation of the ORR activity as commonly observed in single‐layer bifunctional ORR/OER electrodes after OER polarization.     

Controlled Fabrication of Hierarchically Structured Nitrogen‐Doped Carbon Nanotubes as a Highly Active Bifunctional Oxygen Electrocatalyst

Hierarchically structured nitrogen‐doped carbon nanotube (NCNT) composites, with copper (Cu) nanoparticles embedded uniformly within the nanotube walls and cobalt oxide (Co_xO_y) nanoparticles decorated on the nanotube surfaces, are fabricated via a combinational process. This process involves the growth of Cu embedded CNTs by low‐ and high‐temperature chemical vapor deposition, post‐treatment with ammonia for nitrogen doping of these CNTs, precipitation‐assisted separation of NCNTs from cobalt nitrate aqueous solution, and finally thermal annealing for Co_xO_y decoration. Theoretical calculations show that interaction of Cu nanoparticles with CNT walls can effectively decrease the work function of CNT surfaces and improve adsorption of hydroxyl ions onto the CNT surfaces. Thus, the activities of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are significantly enhanced. Because of this benefit, further nitrogen doping, and synergistic coupling between Co_xO_y and NCNTs, Cu@NCNT/Co_xO_y composites exhibit ORR activity comparable to that of commercial Pt/C catalysts and high OER activity (outperforming that of IrO₂ catalysts). More importantly, the composites display superior long‐term stability for both ORR and OER. This simple but general synthesis protocol can be extended to design and synthesis of other metal/metal oxide systems for fabrication of high‐performance carbon‐based electrocatalysts with multifunctional catalytic activities.     

Polyformamidine‐Derived Non‐Noble Metal Electrocatalysts for Efficient Oxygen Reduction Reaction

A facile approach for the template‐free synthesis of highly active non‐noble metal based oxygen reduction reaction (ORR) electrocatalysts is presented. Porous Fe?N?C/Fe/Fe₃C composite materials are obtained by pyrolysis of defined precursor mixtures of polyformamidine (PFA) and FeCl₃ as nitrogen‐rich carbon and iron sources, respectively. Selection of pyrolysis temperature (700–1100 °C) and FeCl₃ loading (5–30 wt%) yields materials with differing surface areas, porosity, graphitization degree, nitrogen and iron content, as well as ORR activity. While the ORR activity of Fe‐free materials is limited (i.e., synthesized from pure PFA), a huge increase in activity is observed for catalysts containing Fe, revealing the participation of the metal dopant in the construction of active electrocatalytic sites. Further activity improvement is achieved via acid‐leaching and repeated pyrolysis, a result which is attributed to the creation of new active sites located at the surface of the porous nitrogen‐doped carbon by dissolution of the Fe and Fe₃C nanophases. The best performing catalyst, which was synthesized with a low Fe loading (i.e., 5 wt%) and at a pyrolysis temperature of 900 °C, exhibits high activity, excellent H₂O selectivity, extended stability, in both basic and acidic media as well as a remarkable tolerance toward methanol.     

Engineering Fe–Fe3C@Fe–N–C Active Sites and Hybrid Structures from Dual Metal–Organic Frameworks for Oxygen Reduction Reaction in H2–O2 Fuel Cell and Li–O2 Battery

Dual metal–organic frameworks (MOFs, i.e., MIL‐100(Fe) and ZIF‐8) are thermally converted into Fe–Fe₃C‐embedded Fe–N‐codoped carbon as platinum group metal (PGM)‐free oxygen reduction reaction (ORR) electrocatalysts. Pyrolysis enables imidazolate in ZIF‐8 rearranged into highly N‐doped carbon, while Fe from MIL‐100(Fe) into N‐ligated atomic sites concurrently with a few Fe–Fe₃C nanoparticles. Upon precise control of MOF compositions, the optimal catalyst is highly active for the ORR in half‐cells (0.88 V in base and 0.79 V versus RHE in acid in half‐wave potential), a proton exchange membrane fuel cell (0.76 W cm^?2 in peak power density) and an aprotic Li–O₂ battery (8749 mAh g^?1 in discharge capacity), representing a state‐of‐the‐art PGM‐free ORR catalyst. In the material, amorphous carbon with partial graphitization ensures high active site exposure and fast charge transfer simultaneously. Macropores facilitate mass transport to the catalyst surface, followed by oxygen penetration in micropores to reach the infiltrated active sites. Further modeling simulations shed light on the true Fe–Fe₃C contribution to the catalyst performance, suggesting Fe₃C enhances oxygen affinity, while metallic Fe promotes *OH desorption as the rate‐determining step at the nearby Fe–N–C sites. These findings demonstrate MOFs as model system for rational design of electrocatalyst for energy‐based functional applications.     

Pyridinic‐Nitrogen‐Dominated Graphene Aerogels with Fe–N–C Coordination for Highly Efficient Oxygen Reduction Reaction

Here, pyridinic nitrogen dominated graphene aerogels with/without iron incorporation (Fe‐NG and NG) are prepared via a facile and effective process including freeze‐drying of chemically reduced graphene oxide with/without iron precursor and thermal treatment in NH₃. A high doping level of nitrogen has been achieved (up to 12.2 at% for NG and 11.3 at% for Fe‐NG) with striking enrichment of pyridinic nitrogen (up to 90.4% of the total nitrogen content for NG, and 82.4% for Fe‐NG). It is found that the Fe‐NG catalysts display a more positive onset potential, higher current density, and better four‐electron selectivity for ORR than their counterpart without iron incorporation. The most active Fe‐NG exhibits outstanding ORR catalytic activity, high durability, and methanol tolerance ability that are comparable to or even superior to those of the commercial Pt/C catalyst at the same catalyst loading in alkaline environment. The excellent ORR performance can be ascribed to the synergistic effect of pyridinic N and Fe‐N _x sites (where iron probably coordinates with pyridinic N) that serve as active centers for ORR. Our Fe‐NG can be developed into cost‐effective and durable catalysts as viable replacements of the expensive Pt‐based catalysts in practical fuel cell applications.     

Hollow Loofah‐Like N,O‐Co‐Doped Carbon Tube for Electrocatalysis of Oxygen Reduction

Designing a highly active doped‐carbon‐based oxygen reduction reaction (ORR) electrocatalyst with optimal stability is a must if large‐scale implementations of fuel cells are to be realized. Developing controllable doping strategies is essential for achieving highly active catalysts. Herein, a facile doping strategy is developed by designing a precursor material with unique core–shell nanostructure, whereby the Materials Institute Lavoisier (MIL) metal–organic framework (MOF) and polyaniline are core and shell components, and serving as oxygen and nitrogen precursors, respectively. A novel hollow loofah‐like carbon tube (HLCT) catalyst is derived from precursor material with controllable heteroatom‐doping concentrations through modulating the mass ratio of MOF/aniline. The optimal HLCT‐1/2 catalyst, with a MOF/aniline mass ratio of 1/2, exhibits excellent ORR activity and stability in an alkaline medium. Remarkably, the half‐wave potential (0.88 V) and the current density (4.35 mA cm^?2) at 0.85 V of HLCT‐1/2 catalyst surpass that of commercial Pt/C. Such superior catalytic properties can be attributed to the high specific surface area and abundant active sites of loofah‐shape carbon tubes. Moreover, the O dopant modulates the content and distribution of N species, leading to the enhanced adsorption strength of oxygen molecules on catalyst surface, promoting the activation of oxygen, and thus achieving higher electrocatalytic activity.     

Iron Oxide Nanoparticle‐Encapsulated CNT Branches Grown on 3D Ozonated CNT Internetworks for Lithium‐Ion Battery Anodes

Multidimensional hierarchical architecturing is a promising chemical approach to provide unique characteristics synergistically integrated from individual nanostructured materials for energy storage applications. Herein, hierarchical complex hybrid architectures of CNT‐on‐OCNT‐Fe are reported, where iron oxide nanoparticles are encapsulated inside carbon nanotube (CNT) branches grown onto the ozone‐treated surface of 3D CNT internetworked porous structures. The activated surface of the 3D ozonated CNT (OCNT) interacts with the iron oxide nanoparticles, resulting in different chemical environments of inner and outer tubes and large surface area. The mixed phases of iron oxide nanoparticles are confined by full encapsulation inside the conductive nanotubes and act as catalysts to vertically grow the CNT branches. This unique hierarchical architecture allows CNT‐on‐OCNT‐Fe to achieve a reasonable capacity of >798 mA h g^?1 at 50 mA g^?1, with outstanding rate capability (≈72% capacity retention at rates from 50 to 1000 mA g^?1) and cyclic stability (>98.3% capacity retention up to 200 cycles at 100 mA g^?1 with a coulombic efficiency of >97%). The improved rate and cyclic capabilities are attributed to the hierarchical porosity of 3D OCNT internetworks, the shielding of CNT walls for encapsulated iron oxide nanoparticles, and a proximate electronic pathway for the isolated nanoparticles.     

Nanoporous Graphene Enriched with Fe/Co‐N Active Sites as a Promising Oxygen Reduction Electrocatalyst for Anion Exchange Membrane Fuel Cells

Here, a simple but efficient way is demonstrated for the preparation of nanoporous graphene enriched with Fe/Co–nitrogen‐doped active sites (Fe/Co‐NpGr) as a potential electrocatalyst for the electrochemical oxygen reduction reaction (ORR) applications. Once graphene is converted into porous graphene (pGr) by a controlled oxidative etching process, pGr can be converted into a potential electrocatalyst for ORR by utilizing the created edge sites of pGr for doping nitrogen and subsequently to utilize the doped nitrogens to build Fe/Co coordinated centers (Fe/Co‐NpGr). The structural information elucidated using both XPS and TOF‐SIMS study indicates the presence of coordination of the M–N (M = Fe and Co)‐doped carbon active sites. Creation of this bimetallic coordination assisted by the nitrogen locked at the pore openings is found to be helping the system to substantially reduce the overpotential for ORR. A 30 mV difference in the overpotential (η) with respect to the standard Pt/C catalyst and high retention in half wave potential after 10 000 cycles in ORR can be attained. A single cell of an anion exchange membrane fuel cell (AEMFC) by using Fe/Co‐NpGr as the cathode delivers a maximum power density of ≈35 mWcm^?2 compared to 60 mWcm^?2 displayed by the Pt‐based system.     

Reduced Graphene Oxide‐Modified Carbon Nanotube/Polyimide Film Supported MoS2 Nanoparticles for Electrocatalytic Hydrogen Evolution

Efficient evolution of hydrogen through electrocatalysis at low overpotentials holds tremendous promise for clean energy. Herein, a highly active and stable MoS₂ electrocatalyst is supported on reduced graphene oxide‐modified carbon nanotube/polyimide (PI/CNT‐RGO) film for hydrogen evolution reaction (HER). The PI/CNT‐RGO film allows the intimate growth of MoS₂ nanoparticles on its surface. The nanosize and high dispersion of MoS₂ nanoparticles provide a vast amount of available edge sites and the coupling of RGO and MoS₂ enhances the electron transfer between the edge sites and the substrate, greatly improving the HER activity of PI/CNT‐RGO‐MoS₂ film. The MoS₂ with a smaller loading less than 0.04 mg cm^?2 on the PI/CNT‐RGO film exhibits excellent HER activities with a low overpotential of 0.09 V and large current densities, as well as good stability. The Tafel slope of 61 mV dec^?1 reveals the Volmer–Heyrovsky mechanism for HER. Thus, this work paves a potential pathway for designing efficient MoS₂‐based electrocatalysts for HER.     

The Quasi‐Pt‐Allotrope Catalyst: Hollow PtCo@single‐Atom Pt1 on Nitrogen‐Doped Carbon toward Superior Oxygen Reduction

Single‐atom Pt and bimetallic Pt₃Co are considered the most promising oxygen reduction reaction (ORR) catalysts, with a much lower price than pure Pt. The combination of single‐atom Pt and bimetallic Pt₃Co in a highly active nanomaterial, however, is challenging and vulnerable to agglomeration under realistic reaction conditions, leading to a rapid fall in the ORR. Here, a sustainable quasi‐Pt‐allotrope catalyst, composed of hollow Pt₃Co (H‐PtCo) alloy cores and N‐doped carbon anchoring single atom Pt shells (Pt₁N‐C), is constructed. This unique nanoarchitecture enables the inner and exterior spaces to be easily accessible, exposing an extra‐high active surface area and active sites for the penetration of both aqueous and organic electrolytes. Moreover, the novel Pt₁N‐C shells not only effectively protect the H‐PtCo cores from agglomeration but also increase the efficiency of the ORR in virtue of the isolated Pt atoms. Thus, the H‐PtCo@Pt₁N‐C catalyst exhibits stable ORR without any fade over a prolonged 10 000 cycle test at 0.9 V in HClO₄ solution. Furthermore, this material can offer efficient and stable ORR activities in various organic electrolytes, indicating its great potential for next‐generation lithium–air batteries as well.     

MO‐Co@N‐Doped Carbon (M = Zn or Co): Vital Roles of Inactive Zn and Highly Efficient Activity toward Oxygen Reduction/Evolution Reactions for Rechargeable Zn–Air Battery

A highly efficient bifunctional oxygen catalyst is required for practical applications of fuel cells and metal–air batteries, as oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are their core electrode reactions. Here, the MO‐Co@N‐doped carbon (NC, M = Zn or Co) is developed as a highly active ORR/OER bifunctional catalyst via pyrolysis of a bimetal metal–organic framework containing Zn and Co, i.e., precursor (CoZn). The vital roles of inactive Zn in developing highly active bifunctional oxygen catalysts are unraveled. When the precursors include Zn, the surface contents of pyridinic N for ORR and the surface contents of Co–N_x and Co³⁺/Co²⁺ ratios for OER are enhanced, while the high specific surface areas, high porosity, and high electrochemical active surface areas are also achieved. Furthermore, the synergistic effects between Zn‐based and Co‐based species can promote the well growth of multiwalled carbon nanotubes (MWCNTs) at high pyrolysis temperatures (≥700 °C), which is favorable for charge transfer. The optimized CoZn‐NC‐700 shows the highly bifunctional ORR/OER activity and the excellent durability during the ORR/OER processes, even better than 20 wt% Pt/C (for ORR) and IrO₂ (for OER). CoZn‐NC‐700 also exhibits the prominent Zn–air battery performance and even outperforms the mixture of 20 wt% Pt/C and IrO₂.     

Hierarchical NiMn Layered Double Hydroxide/Carbon Nanotubes Architecture with Superb Energy Density for Flexible Supercapacitors

A hierarchical nanostructure composed of NiMn‐layered double hydroxide (NiMn‐LDH) microcrystals grafted on carbon nanotube (CNT) backbone is constructed by an in situ growth route, which exhibits superior supercapacitive performance. The resulting composite material (NiMn‐LDH/CNT) displays a three‐dimensional architecture with tunable Ni/Mn ratio, well‐defined core‐shell configuration, and enlarged surface area. An electrochemical investigation shows that the Ni₃Mn₁‐LDH/CNT electrode is rather active, which delivers a maximum specific capacitance of 2960 F g^–1 (at 1.5 A g^–1), excellent rate capability (79.5% retention at 30 A g^–1), and cyclic stability. Moreover, an all‐solid‐state asymmetric supercapacitor (SC) with good flexibility is fabricated by using the NiMn‐LDH/CNT film and reduced graphene oxide (RGO)/CNT film as the positive and negative electrode, respectively, exhibiting a wide cell voltage of 1.7 V and largely enhanced energy density up to 88.3 Wh kg^–1 (based on the total weight of the device). By virtue of the high‐capacity of pseudocapacitive hydroxides and desirable conductivity of carbon‐based materials, the monolithic design demonstrated in this work provides a promising approach for the development of flexible energy storage systems.     

Facile Synthesis of Manganese‐Oxide‐Containing Mesoporous Nitrogen‐Doped Carbon for Efficient Oxygen Reduction

Developing low‐cost non‐precious metal catalysts for high‐performance oxygen reduction reaction (ORR) is highly desirable. Here a facile, in situ template synthesis of a MnO‐containing mesoporous nitrogen‐doped carbon (m‐N‐C) nanocomposite and its high electrocatalytic activity for a four‐electron ORR in alkaline solution are reported. The synthesis of the MnO‐m‐N‐C nanocomposite involves one‐pot hydrothermal synthesis of Mn₃O₄@polyaniline core/shell nanoparticles from a mixture containing aniline, Mn(NO₃)₂, and KMnO₄, followed by heat treatment to produce N‐doped ultrathin graphitic carbon coated MnO hybrids and partial acid leaching of MnO. The as‐prepared MnO‐m‐N‐C composite catalyst exhibits high electrocatalytic activity and dominant four‐electron oxygen reduction pathway in 0.1 M KOH aqueous solution due to the synergetic effect between MnO and m‐N‐C. The pristine MnO shows little electrocatalytic activity and m‐N‐C alone exhibits a dominant two‐electron process for ORR. The MnO‐m‐N‐C composite catalyst also exhibits superior stability and methanol tolerance to a commercial Pt/C catalyst, making the composite a promising cathode catalyst for alkaline methanol fuel cell applications. The synergetic effect between MnO and N‐doped carbon described provides a new route to design advanced catalysts for energy conversion.     

Luminescence of Functionalized Carbon Nanotubes as a Tool to Monitor Bundle Formation and Dissociation in Water: The Effect of Plasmid‐DNA Complexation

Functionalized carbon nanotubes (f‐CNTs) are explored as novel nanomaterials for biomedical applications. UV‐vis luminescence of aqueous dispersions of CNT–NH₃⁺ and CNT–NH–Ac (NH–Ac: acetamido) is observed using standard laboratory spectrophotometric instrumentation, and the measured fluorescence intensity is correlated with the aggregation state of the f‐CNTs: a high intensity indicates improved f‐CNT individualization and dispersion, while a decrease in fluorescence intensity indicates a higher degree of nanotube aggregation and bundling as a result of varying the sodium dodecyl sulfate (SDS) concentrations and pH in the aqueous phase. Moreover, utilization of this relationship between fluorescence intensity and the state of f‐CNT aggregation is carried out to elucidate the interactions between f‐CNTs and gene‐encoding plasmid DNA (pDNA). pDNA is shown to interact with CNT–NH₃⁺ primarily through electrostatic interactions that lead concomitantly to a higher degree of f‐CNT bundling. The CNT–NH₃⁺/pDNA interactions are successfully competed by SDS/f‐CNT surface interactions, resulting in the displacement of pDNA. These studies provide exemplification of the use of fluorescence spectrophotometry to accurately describe the aggregation state of water‐soluble f‐CNTs. Characterization of the complexes between pDNA and f‐CNTs elucidates the opportunities and limitations of such supramolecular systems as potential vectors for gene transfer.     

CuCo Bimetallic Oxide Quantum Dot Decorated Nitrogen‐Doped Carbon Nanotubes: A High‐Efficiency Bifunctional Oxygen Electrode for Zn–Air Batteries

The large‐scale production of metal–air batteries, an appealing solution for next‐generation energy storage, requires low‐cost, earth‐abundant, and efficient oxygen electrode materials, yet insights into active catalyst structures and synergistic reactivity remain largely unknown. Here, a new bifunctional oxygen electrode based on nitrogen‐doped carbon nanotubes decorated by spinel CuCo₂O₄ quantum dots (CuCo₂O₄/N‐CNTs) is reported, outperforming the benchmark of state‐of‐the‐art noble metal catalysts. Combining spectroscopic characterization and electrochemical studies, a prominent synergetic effect between CuCo₂O₄ and N‐doped carbon nanotubes is uncovered: the high conductivity, large active surface area, and increase in the number of catalytic sites induced by Cu doping (i.e., Cu²⁺ and Cu?N) can be beneficial to the overall electrocatalytic activities. Remarkably, the native flexibility of CuCo₂O₄/N‐CNTs allows its direct use as reversible oxygen electrodes in Zn–air batteries either with liquid alkaline electrolyte or in the all‐solid‐state configuration. The prepared devices demonstrate excellent discharging/charging performance, large energy density (83.83 mW cm^?2 in liquid state, 1.86 W g^?1 in all‐solid‐state), and long lifetime (48 h in liquid state, 9 h in all‐solid‐state), holding great promise in the practical application of rechargeable metal–air batteries and other fuel cells.     

A Hybrid Supercapacitor Fabricated with a Carbon Nanotube Cathode and a TiO2–B Nanowire Anode

Recently, a new hybrid supercapacitor, integrating both the advantages of supercapacitors and lithium‐ion batteries, was proposed and rapidly turned into state‐of‐the‐art energy‐storage devices with a high energy density, fast power capability, and a long cycle life. In this paper, a new hybrid supercapacitor is fabricated by making use of the benefits of 1D nanomaterials consisting of a carbon nanotube (CNT) cathode and a TiO₂–B nanowire (TNW) anode, and the preliminary results for such an energy‐storage device operating over a wide voltage range (0–2.8 V) are presented. The CNT–TNW supercapacitor is compared to a CNT–CNT supercapacitor, and discussed with regards to available energy densities, power capabilities, voltage profiles, and cycle life. On the basis of the total weight of both active materials, the CNT–TNW supercapacitor delivers an energy density of 12.5 W h kg^–1 at a rate of 10 C, double the value of the CNT–CNT supercapacitor, while maintaining desirable cycling stability. The combination of a CNT cathode and a TNW anode in a non‐aqueous electrolyte is proven to be suitable for high‐performance hybrid supercapacitor applications; this can reasonably be assigned to the interesting synergistic effects of the two nanomaterials. It is hoped that the results presented in this study might renew interest in the design of nanomaterials that are applicable not only to hybrid supercapacitors, but also to energy conversion and storage applications of the future.     

Structurally Ordered Low‐Pt Intermetallic Electrocatalysts toward Durably High Oxygen Reduction Reaction Activity

Carbon‐supported low‐Pt ordered intermetallic nanoparticulate catalysts (PtM₃, M = Fe, Co, and Ni) are explored in order to enhance the oxygen reduction reaction (ORR) activity while achieving a high stability compared to previously reported Pt‐richer ordered intermetallics (Pt₃M and PtM) and low‐Pt disordered alloy catalysts. Upon high‐temperature thermal annealing, ordered PtCo₃ intermetallic nanoparticles are successfully prepared with minimum particle sintering. In contrast, the PtFe₃ catalyst, despite the formation of ordered structure, suffers from obvious particle sintering and detrimental metal–support interaction, while the PtNi₃ catalyst shows no structural ordering transition at all but significant particle sintering. The ordered PtCo₃ catalyst exhibits durably thin Pt shells with a uniform thickness below 0.6 nm (corresponding to 2–3 Pt atomic layers) and a high Co content inside the nanoparticles after 10 000 potential cycling, leading to a durably compressive Pt surface and thereby both high activity (fivefold vs a commercial Pt catalyst and 1.7‐fold vs an ordered PtCo intermetallic catalyst) and high durability (5 mV loss in half‐wave potential and 9% drop in mass activity). These results provide a new strategy toward highly active and durable ORR electrocatalysts by rational development of low‐Pt ordered intermetallics.     

Molybdenum Phosphide/Carbon Nanotube Hybrids as pH‐Universal Electrocatalysts for Hydrogen Evolution Reaction

Molybdenum phosphide (MoP) has received increasing attention due to its high catalytic activity in hydrogen evolution reaction (HER). However, it remains difficult to construct well‐defined MoP nanostructures with large density of active sites and high intrinsic activity. Here, a facile and general method is reported to synthesize an MoP/carbon nanotube (CNT) hybrid featuring small‐sized and well‐crystallized MoP nanoparticles uniformly coated on the sidewalls of multiwalled CNT. The MoP/CNT hybrid exhibits impressive HER activities in pH‐universal electrolytes, and requires the overpotentials as low as 83, 102, and 86 mV to achieve a cathodic current density of 10 mA cm^?2 in acidic 0.5 m H₂SO₄, neutral 1 m phosphate buffer solution, and alkaline 1 m KOH electrolytes, respectively. It is found that the crystallinity of MoP has significant influence on HER activity. This study provides a new design strategy to construct MoP nanostructures for optimizing its catalytic performance.     

Stabilizing Active Edge Sites in Semicrystalline Molybdenum Sulfide by Anchorage on Nitrogen‐Doped Carbon Nanotubes for Hydrogen Evolution Reaction

Finding an abundant and cost‐effective electrocatalyst for the hydrogen evolution reaction (HER) is crucial for a global production of hydrogen from water electrolysis. This work reports an exceptionally large surface area hybrid catalyst electrode comprising semicrystalline molybdenum sulfide (MoS_2+x) catalyst attached on a substrate based on nitrogen‐doped carbon nanotubes (N‐CNTs), which are directly grown on carbon fiber paper (CP). It is shown here that nitrogen‐doping of the carbon nanotubes improves the anchoring of MoS_2+x catalyst compared to undoped carbon nanotubes and concurrently stabilizes a semicrystalline structure of MoS_2+x with a high exposure of active sites for HER. The well‐connected constituents of the hybrid catalyst are shown to facilitate electron transport and as a result of the good attributes, the MoS_2+x/N‐CNT/CP electrode exhibits an onset potential of ?135 mV for HER in 0.5 m H₂SO₄, a Tafel slope of 36 mV dec^?1, and high stability at a current density of ?10 mA cm^?2.