Molybdenum Carbide-Decorated Metallic Cobalt@Nitrogen-Doped Carbon Polyhedrons for Enhanced Electrocatalytic Hydrogen Evolution

Synergistic effects of interface and phase engineering on telluride toward alkaline/neutral hydrogen evolution reaction in freshwater/seawater

The development of efficient, stable, and versatile hydrogen evolution electrocatalysts is of great meaning, but still faces challenging. Interface engineering and phase engineering have been immensely applied in the field of hydrogen evolution reaction (HER) because of their unique physicochemical properties. However, they are typically used separately, which limits their effectiveness. Herein, we propose an interface-engineered CoMo/CoTe electrocatalyst, consisting of an amorphous CoMo (a-CoMo) layer-encapsulated crystalline CoTe array, achieving the profound optimization of catalytic performance. The experimental results and density functional theory calculations show that the d-band center of the catalyst shifts further upward in contrast with its crystalline-crystalline counterpart, optimizing the electronic structure and the intermediate adsorption, thereby reducing the kinetic barrier of HER. The a-CoMo/CoTe with superhydrophilic/superaerophobic features shows excellent catalytic performance in alkaline, neutral, and simulated seawater environments.

Cobalt-Based Nanoscale Material: An Emerging Electrocatalyst for Hydrogen Production

Modern civilization has been highly suffering from energy crisis and environmental pollutions. These two burning issues are directly and indirectly created from fossil fuel consumption and uncontrolled industrialization. The above critical issue can be solved through the proper utilization of green energy sources where no greenhouse gases will be generated upon burning of such materials. Hydrogen is the most eligible candidate for this purpose. Among various methods of hydrogen generation, electrocatalytic process is one of the most efficient methods because of easy handling and high efficiency. In these aspects Co-based nanomaterials are considered to be extremely significant as they can be utilized as efficient, recyclable and ideal catalytic system. In this article a series of Co-based nano-electrocatalysts has been discussed with proper structure-property relationship and their medium dependency. Therefore, such type of stimulating summary on recently reported electrocatalysts and their activity may be helpful for scientists of the corresponding field as well as for broader research communities. This can be inspiration for materials researchers to fabricate active catalysts for the production of hydrogen gas in room temperature.

Atomic Confinement Empowered CoZn Dual-Single-Atom Nanotubes for H2O2 Production in Sequential Dual-Cathode Electro-Fenton Process

Single-atom catalysts (SACs) are flourishing in various fields because of their 100% atomic utilization. However, their uncontrollable selectivity, poor stability and vulnerable inactivation remain critical challenges. According to theoretical predictions and experiments, a heteronuclear CoZn dual-single-atom confined in N/O-doped hollow carbon nanotube reactors (CoZnSA@CNTs) is synthesized via spatial confinement growth. CoZnSA@CNTs exhibit superior performance for H2O2 electrosynthesis over the entire pH range due to dual-confinement of atomic sites and O2 molecule. CoZnSA@CNTs is favorable for H2O2 production mainly because the synergy of adjacent atomic sites, defect-rich feature and nanotube reactor promoted O2 enrichment and enhanced H2O2 reactivity/selectivity. The H2O2 selectivity reaches ∼100% in a range of 0.2-0.65 V versus RHE and the yield achieves 7.50 M gcat -1 with CoZnSA@CNTs/carbon fiber felt, exceeding most of the reported SACs in H-type cells. The obtained H2O2 is converted directly to sodium percarbonate and sodium perborate in a safe way for H2O2 storage/transportation. The sequential dual-cathode electron-Fenton process promotes the formation of reactive oxygen species (•OH, 1O2 and •O2 -) by activating the generated H2O2, enabling accelerated degradation of various pollutants and Cr(VI) detoxification in actual wastewater. This work proposes a promising confinement strategy for catalyst design and selectivity regulation of complex reactions.

Pt nanoparticles-decorated molybdenum nitrides for efficient hydrogen evolution reaction

Exploring low cost and high efficiency catalysts for hydrogen production from electrochemical water splitting is preferable and remains a significant challenge. As an alternative to Pt-based catalysts, molybdenum nitrides have attracted more attention for their hydrogen evolution reaction (HER). However, their performance is restricted due to the strong bonding of Mo-H. Herein, molybdenum nitrides with Pt-doping are fabricated to enhance the catalytic activity for HER in acidic solution. As expected, Pt (5 wt%)-MoNx delivers a low overpotential of 47 mV at a current density of 10 mA cm-2 with a high exchange current density (j0 = 0.98 mA cm-2). The superior performance is attributed to the modified electronic structure of Mo with Pt incorporation.

Recent Tendency on Transition-Metal Phosphide Electrocatalysts for the Hydrogen Evolution Reaction in Alkaline Media

Hydrogen energy is regarded as an auspicious future substitute to replace fossil fuels, due to its environmentally friendly characteristics and high energy density. In the pursuit of clean hydrogen production, there has been a significant focus on the advancement of effective electrocatalysts for the process of water splitting. Although noble metals like Pt, Ru, Pd and Ir are superb electrocatalysts for the hydrogen evolution reaction (HER), they have limitations for large-scale applications, mainly high cost and low abundance. As a result, non-precious transition metals have emerged as promising candidates to replace their more expensive counterparts in various applications. This review focuses on recently developed transition metal phosphides (TMPs) electrocatalysts for the HER in alkaline media due to the cooperative effect between the phosphorus and transition metals. Finally, we discuss the challenges of TMPs for HER.

Vacancy effect on the electrocatalytic activity of LaMn1/2Co1/2O3-δ for hydrogen and oxygen evolution reactions

Development of efficient electrocatalysts for water splitting can be a significant step toward green hydrogen generation. In this work, a remarkable enhancement of electrocatalytic properties is achieved through the incorporation of oxygen-vacancies in a perovskite oxide, while maintaining the same structural framework. The oxygen-deficient material La₂MnCoO_6-δ (LaMn_0.5Co_0.5O_3-δ) is isostructural to the parent stoichiometric material, but shows drastically enhanced electrocatalytic properties for both half-reactions of water-splitting, namely hydrogen-evolution and oxygen-evolution reactions, due to the oxygen-vacancies.

Urchin-Like Structured MoO2 /Mo3 P/Mo2 C Triple-Interface Heterojunction Encapsulated within Nitrogen-Doped Carbon for Enhanced Hydrogen Evolution Reaction

The development of highly efficient and cost-effective hydrogen evolution reaction (HER) catalysts is highly desirable to efficiently promote the HER process, especially under alkaline condition. Herein, a polyoxometalates-organic-complex-induced carbonization method is developed to construct MoO₂ /Mo₃ P/Mo₂ C triple-interface heterojunction encapsulated into nitrogen-doped carbon with urchin-like structure using ammonium phosphomolybdate and dopamine. Furthermore, the mass ratio of dopamine and ammonium phosphomolybdate is found critical for the successful formation of such triple-interface heterojunction. Theoretical calculation results demonstrate that such triple-interface heterojunctions possess thermodynamically favorable water dissociation Gibbs free energy (ΔG_H2O ) of -1.28 eV and hydrogen adsorption Gibbs free energy (ΔG_H* ) of -0.41 eV due to the synergistic effect of Mo₂ C and Mo₃ P as water dissociation site and H* adsorption/desorption sites during the HER process in comparison to the corresponding single components. Notably, the optimal heterostructures exhibit the highest HER activity with the low overpotential of 69 mV at the current density of 10 mA cm^-2 and a small Tafel slope of 60.4 mV dec^-1 as well as good long-term stability for 125 h. Such remarkable results have been theoretically and experimentally proven to be due to the synergistic effect between the unique heterostructures and the encapsulated nitrogen-doped carbon.

Achieving near-Pt hydrogen production on defect nanocarbon via the synergy between carbon defects and heteroatoms

The effect of the synergy between vacancy defects and a phosphorus dopant on the hydrogen evolution reaction (HER) of nanocarbon was revealed for the first time both experimentally and theoretically, and the as-prepared catalysts show near-Pt HER activities, which are the best among metal-free catalysts.

Screening Nickel-Doped Mo2 C Nanorod Arrays for Ultrastable and Efficient Hydrogen Evolution over a Wide pH Range

Green hydrogen, using sustainable energy to decompose water to produce hydrogen, is regarded as the ideal and effective connection to convert electricity into chemical energy. Herein, well designed Ni-doped Mo₂ C nanorod electrodes self-supported on three types of substrates (Ni foam, Cu foam and stainless steel wire mesh) with outstanding gas resistance and prominent corrosion resistance were assembled together to build up a wide pH applicable electrode for Hydrogen Evolution. In particular, Ni-doped Mo₂ C nanorod arrays on stainless steel wire mesh donated as Ni-Mo₂ C@SSW exhibited remarkable electrocatalytic properties towards hydrogen evolution reaction with superior overpotentials both in 1 M KOH and 0.5 M H₂ SO₄ (102 mV and 106 mV at the current density of 10 mA cm^-2 ) and incomparable continuous durability. This work provides the possibility for the realization of low cost, high activity and ultra-stable durability HER electrocatalysts in practical industrial application.

Boosting the activity and stability via synergistic catalysis of Co nanoparticles and MoC to construct a bifunctional electrocatalyst for high-performance and long-life rechargeable zinc-air batteries

The high overpotential of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) leading to slow air cathode kinetics is still a major challenge for zinc-air batteries (ZABs), hindering the commercialization of ZABs. With the advantages of cost-effectiveness and feasibility of synthesis at room temperature, zeolite imidazole frameworks (ZIFs) are regarded as advanced precursors. But a majority of ZIF-derived catalysts show only one catalytic activity, which limits their performance in ZABs as well as the cycling stability. In addition, molybdenum carbide (MoC) is recognized as an excellent candidate for renewable energy conversion due to its good chemical resistance and thermal stability. Herein, we report a ZIF-67-derived Co/MoC-NC multiphase doped carbon bifunctional ORR/OER catalyst with multiple active sites for the cathode of ZABs. The synergistic catalysis of Co nanoparticles and MoC nanoparticles in Co/MoC-NC which are embedded in a thin layer of N-doped graphitic carbon and immobilized on N-doped graphitic carbon, respectively, demonstrates superior ORR catalytic performance and durability both under alkaline and acidic conditions (E_1/2 = 0.87 V in 1.0 M KOH and E_1/2 = 0.76 V in 0.5 M H₂SO₄). Simultaneously, Co/MoC-NC also exhibits favorable OER performance (10 mA cm^-2, η = 320 mV) in 1 M KOH. Furthermore, a remarkable peak-power density of 215.36 mW cm^-2 and great cycling stability could be achieved while applying Co/MoC-NC in the cathode of ZABs (over 300 h). This work will provide a viable design concept for designing and synthesizing multifunctional catalysts to construct rechargeable ZABs.

Zeolite Imidazolate Frameworks (ZIFs) Derived Nanomaterials and their Hybrids for Advanced Secondary Batteries and Electrocatalysis

Zeolite imidazolate frameworks (ZIFs), as a typical class of metal-organic frameworks (MOFs), have attracted a great deal of attention in the field of energy storage and conversation due to their chemical structure stability, facile synthesis and environmental friendliness. Among of ZIFs family, the zinc-based imidazolate framework (ZIF-8) and cobalt-based imidazolate framework (ZIF-67) have considered as promising ZIFs materials, which attributed to their tunable porosity, stable structure, and desirable electrical conductivity. To date, various ZIF-8 and ZIF67 derived materials, including carbon materials, metal oxides, sulfides, selenides, carbides and phosphides, have been successfully synthesized using ZIFs as templates and evaluated as promising electrode materials for secondary batteries and electrocatalysis. This review provides an effective guide for the comprehension of the performance optimization and application prospects of ZIFs derivatives, specifically focusing on the optimization of structure and their application in secondary batteries and electrocatalysis. In detail, we present recent advances in the improvement of electrochemical performance of ZIF-8, ZIF-67 and ZIF-8@ZIF-67 derived nanomaterials and their hybrids, including carbon materials, metal oxides, carbides, oxides, sulfides, selenides, and phosphides for high-performance secondary batteries and electrocatalysis.

Graphene-like sheets supported Fe-Co layered double hydroxides nanoflakes as an efficient electrocatalyst for both hydrogen and oxygen evolution reaction, A green investigation

Herein, a nanohybrid material containing graphene-like sheets (GS) and Fe-Co layered double hydroxides nanoflakes (LDHs) was synthesized via simple two-step processes and named Fe-Co LDHs/GS. The Fe-Co LDHs/GS nanohybrid was characterized by various techniques. Fe-Co LDHs nanoflakes were grown on GS in Fe-Co LDHs/GS nanohybrid. The electrochemical surface area of Fe-Co LDHs/GS nanohybrid was obtained 0.05 cm² based on the Randles-Sevcik equation. The Fe-Co LDHs/GS nanohybrid was applied as an electrocatalyst of HER and OER in a 1.0 M KOH. The electrochemical performance of Fe-Co LDHs/GS nanohybrid was surveyed by several electrochemical methods, and long-term electrochemical stability. The onset potential, overpotential at 10 mA cm^-1 current density, and Tafel slope for the Fe-Co LDHs/GS nanohybrid were obtained -0.33 V, -0.43 V (_vs. RHE), and 122 mV dec^-1, respectively. The Fe-Co LDHs/GS nanohybrid has long-term stability over 35 h in alkaline media toward HER. Furthermore, the onset potential, overpotential at 10 mA/cm, and Tafel slope for the Fe-Co LDHs/GS nanohybrid were obtained as 1.52 V, 1.60 V (vs. RHE), and 44 mV dec^-1, respectively. The Fe-Co LDHs/GS nanohybrid has long-term durability over 10 h in alkaline media toward OER.

Direct Electron Transfer Coordinated by Oxygen Vacancies Boosts Selective Nitrate Reduction to N2 on a Co-CuOx Electroactive Filter

Atomic hydrogen (H*) is used as an important mediator for electrochemical nitrate reduction; however, the Faradaic efficiency (FE) and selective reduction to N₂ are likely compromised due to the side reactions (e.g., ammonia generation and hydrogen evolution reactions). This work reports a Co-CuO_x electrochemical filter with CoO_x nanoclusters rooted on vertically aligned CuO_x nanowalls for selective nitrate reduction to N₂, utilizing the direct electron transfer between oxygen vacancies and nitrate to suppress the contribution by H*. At a cathodic potential of -1.1 V (vs Ag/AgCl), the Co-CuO_x filter showed 95.2% nitrate removal and 96.0% N₂ selectivity at an influent nitrate concentration of 20 N-mg L^-1. Meanwhile, the energy consumption and FE were 0.60 kW h m^-3 and 53.5%, respectively, at a permeate flux of 60 L m^-2 h^-1. The presence of abundant oxygen vacancies on Co-CuO_x was due to the change in the electron density of the Cu atom and a decrease of the coordination numbers of Cu-O via cobalt doping. Theoretical calculations and electrochemical tests showed that the oxygen vacancies coordinated nitrate adsorption and subsequent reduction reactions, thus suppressing the contribution of H* to nitrate reduction and leading to a thermodynamically favorable process to N₂ via direct electron transfer.

Probing the Impact of Tribolayers on Enhanced Wear Resistance Behavior of Carbon-Rich Molybdenum-Based Coatings

Minimizing friction and wear is one of the continuing challenges in many mechanical industries. Recent research efforts have been focused on accelerating the antifriction and antiwear properties of hard coatings through the incorporation of self-lubricant materials or the development of new architectures. In this present study, carbon-rich MoC, MoCN, and multilayer MoC/MoCN coatings were deposited using reactive magnetron sputtering. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy were used to evaluate their properties, which revealed the presence of ceramic cubic crystallites, covalent bonds between primary elements, and an excess of amorphous carbon (a-C) in all of the coatings. The multilayer architecture and possible segregation of a-C around the ceramic crystallites resulted in improved mechanical properties for all coatings, with MoC/MoCN coatings having a maximum hardness of 21 GPa and elastic modulus of 236 GPa. Friction and wear behavior are initially determined by the structural-composition-property relationships of the respective coatings; later, the tribological characteristics are altered depending on the nature of tribolayer on both mating surfaces at the contact interface. The highest wear resistance of multilayer MoC/MoCN coating (8.7 × 10^-8 mm³/N m) and MoC coating (3.9 × 10^-7 mm³/N m) was due to the dissipation of contact stress by the tribofilm consisting of carbon tribo products like graphitic sp² carbon, diamond-like sp³ carbon, and pyrrolic-N. On the other hand, MoCN coating depicted a lower wear resistance due to the frequent termination of C-H bonds by N, which restricts the strong formation of tribofilms as well as poor mechanical properties.

Recent Status and Challenges in Multifunctional Electrocatalysis Based on 2D MXenes

Due to their chemical and electrical characteristics, such as metallic conductivity, redox-activity in transition metals, high hydrophilicity, and adjustable surface properties, MXenes are emerging as important contributors to oxygen reduction...

Hollow Co nanoparticle/carbon nanotube composite foam for efficient electrocatalytic hydrogen evolution

The electrochemical hydrogen evolution reaction (HER) requires highly efficient electrocatalysts.

Monodisperse Molybdenum Nanoparticles as Highly Efficient Electrocatalysts for Li-S Batteries

Lithium-sulfur (Li-S) batteries have attracted widespread attention due to their high theoretical energy density. However, their practical application is still hindered by the shuttle effect and the sluggish conversion of lithium polysulfides (LiPSs). Herein, monodisperse molybdenum (Mo) nanoparticles embedded onto nitrogen-doped graphene (Mo@N-G) were developed and used as a highly efficient electrocatalyst to enhance LiPS conversion. The weight ratio of the electrocatalyst in the catalyst/sulfur cathode is only 9%. The unfilled d orbitals of oxidized Mo can attract the electrons of LiPS anions and form Mo-S bonds during the electrochemical process, thus facilitating fast conversion of LiPSs. Li-S batteries based on the Mo@N-G/S cathode can exhibit excellent rate performance, large capacity, and superior cycling stability. Moreover, Mo@N-G also plays an important role in room-temperature quasi-solid-state Li-S batteries. These interesting findings suggest the great potential of Mo nanoparticles in building high-performance Li-S batteries.

Phosphorus-decorated Mo-MXene/CQD hybrid: a 2D/0D architecture for bifunctional electrochemical water splitting

The exploration of nonprecious metal-based 2D bifunctional electrocatalysts is of great significance for transforming to sustainable energies in terms of hydrogen. However, to achieve commendable electrocatalytic performance via rational design of surface-interface-engineered Mo-MXene hybrids remain challenging and highly demanding. Herein, we report large size exfoliated Mo-MXene sheets, which provide a flat flexible interface for decoration with carbon quantum dots (CQDs) and controlled surface phosphorization (denoted as Mo-MX/C/P hybrid). The resulting Mo-MX/C/P hybrid exhibited the lowest onset potentials of 14 and 58 mV at an applied current of 0.2 mA cm^-2 for the HER and OER, respectively. Strikingly, the electronegative nature of phosphorous (P) and quick charge transfer between the CQDs and Mo₂CTx matrix were responsible for its superior catalytic activities. Despite the superior performance, the Mo-MX/C/P hybrid can also be used for full-cell division of water with a cell voltage of 1.34 volts at 10 mA cm^-2 and was found to be durable up to 12. This work provides a novel insight into the further development of surface-interface-engineered Mo-MXene hybrids for sustainable energy.

MoS2 and CdMoS4 nanostructure-based UV light photodetectors

We have developed MoS2 nanosheets and CdMoS4 hierarchical nanostructures based on a UV light photodetector. The surface morphologies of the as-prepared samples were investigated via field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The performance parameters for the present photodetectors are investigated under the illumination of UV light having a wavelength of ∼385 nm. Upon the illumination of UV light, the CdMoS4-based photodetector device showed a better response to UV light compared to the MoS2 device in terms of photoresponsivity, response time (∼72 s) and recovery time (∼94 s). Our results reveal that CdMoS4 hierarchical nanostructures are practical for enhancing the device performance.

Boron vacancy: a strategy to boost the oxygen reduction reaction of hexagonal boron nitride nanosheet in hBN-MoS2 heterostructure

The incorporation of vacancies in a system is considered a proficient method of defect engineering in general catalytic modulation. Among two-dimensional materials, the deficiency of surface active sites and a high band gap restrict the catalytic activity of hexagonal boron nitride (hBN) material towards the oxygen reduction reaction (ORR), which hinders its applicability in fuel cells. A bane to boon strategy has been introduced here by coupling two sluggish ORR materials (hBN & MoS2) by a probe-sonication method to form a heterostructure (termed HBPS) which fosters four electron pathways to assist the reduction of oxygen. Theoretical and experimental studies suggest the kinetically and thermodynamically favorable formation of boron vacancies (B-vacancies) in the presence of MoS2, which act as active sites for oxygen adsorption in HBPS. B-vacancy induced uneven charge distribution together with band gap depression promote rapid electron transfer from the valance band to the conduction band which prevails over the kinetic limitation of pure hBN nanosheets towards ORR kinetics. The formed B-vacancy induced HBPS further exhibits a low Tafel slope (66 mV dec-1), and a high onset potential (0.80 V vs. RHE) with an unaltered electrochemically active surface area (ESCA) after long-term cycling. Thus, vacancy engineering in hBN has proved to be an efficient approach to unlock the potential of catalytic performance enhancement.

Self-supporting Atmosphere-Assisted Synthesis of 1D Mo2 C-based Catalyst for Efficient Hydrogen Evolution

One-dimensional materials exhibit fascinating properties in electrocatalytic applications but their fabrication faces the challenge of tedious and complicated operations. We have developed a bottom-up strategy to construct a 1D metal carbide catalyst (Mo₂ C@NC) consisting of ultrafine Mo₂ C nanoparticles embedded within nitrogen-doped carbon layers by simply calcining a mixture of ammonium molybdate, urea and melamine. Experimental results and thermodynamic calculations demonstrate that the retainable pyrolysis-generated self-supporting atmosphere plays a crucial role in the crystalline phase and morphology of materials. When functioned as an electrocatalyst for the hydrogen evolution reaction (HER), the achieved Mo₂ C@NC presents an excellent catalytic activity as well as outstanding stability. This work could shed fresh light onto the facile synthesis of effective HER catalysts with 1D nanostructure.

Earth-Abundant Electrocatalysts for Water Splitting: Current and Future Directions

Of all the available resources given to mankind, the sunlight is perhaps the most abundant renewable energy resource, providing more than enough energy on earth to satisfy all the needs of humanity for several hundred years. Therefore, it is transient and sporadic that poses issues with how the energy can be harvested and processed when the sun does not shine. Scientists assume that electro/photoelectrochemical devices used for water splitting into hydrogen and oxygen may have one solution to solve this hindrance. Water electrolysis-generated hydrogen is an optimal energy carrier to store these forms of energy on scalable levels because the energy density is high, and no air pollution or toxic gas is released into the environment after combustion. However, in order to adopt these devices for readily use, they have to be low-cost for manufacturing and operation. It is thus crucial to develop electrocatalysts for water splitting based on low-cost and land-rich elements. In this review, I will summarize current advances in the synthesis of low-cost earth-abundant electrocatalysts for overall water splitting, with a particular focus on how to be linked with photoelectrocatalytic water splitting devices. The major obstacles that persist in designing these devices. The potential future developments in the production of efficient electrocatalysts for water electrolysis are also described.

Hybrid Transition-Metal Oxide and Nitride@N-Doped Reduced Graphene Oxide Electrodes for High-Performance, Flexible, and All-Solid-State Supercapacitors

Nanoscale composites for high-performance electrodes employed in flexible, all-solid-state supercapacitors are being developed. A series of binder-free composites, each consisting of a transition bimetal oxide, a metal oxide, and a metal nitride grown on N-doped reduced graphene oxide (rGO)-wrapped nickel foam are obtained by using a universal strategy. Three different transition metals, Co, Mo, and Fe, are separately compounded with nickel ions, which originate from the nickel foam, to form three composites, NiCoO₂ @Co₃ O₄ @Co₂ N, NiMoO₄ @MoO₃ @Mo₂ N, and NiFe₂ O₄ @Fe₃ O₄ @Fe₂ N, respectively. These as-prepared active materials have similar regular variation patterns in their properties, including better conductivity and battery-mimicking pseudocapacitance, which result in their high whole-electrode capacitance performance [2598.3 F g^-1 (39.85 F cm^-2 ), 3472.6 F g^-1 (41.43 F cm^-2 ) and 1907.5 F g^-1 (3.41 F cm^-2 ) for the composites incorporating Co, Mo, and Fe, respectively]. The as-assembled flexible, all-solid-state NiCoO₂ @Co₃ O₄ @Co₂ N//KOH/PVA//NiCoO₂ @Co₃ O₄ @Co₂ N device can be easily bent and exhibits high energy density and power density of 92.8 Wh kg^-1 and 1670.4 W kg^-1 , respectively. The universality of this design strategy could allow it to be employed in producing hybrid materials for high-performance energy-storage devices.

In-situ synthesis of ultrasmall Au nanoparticles on bimetallic metal-organic framework with enhanced electrochemical activity for estrone sensing

In this work, ultrasmall Au nanoparticles decorated bimetallic metal-organic framework (US Au NPs@AuZn-MOF) hybrids were facilely prepared by a sequential ion exchange and in-situ chemical reduction strategy. Numerous of Au nanoparticles with size less than 5 nm was homogeneously dispersed on the surface of the whole bimetallic AuZn-MOF polyhedrons. The integration of ultrasmall Au nanoparticles greatly enhanced the electron transfer capacity and electrochemical active surface area of the metal-organic framework host. Compared with the pristine Zn-MOF, bimetallic AuZn-MOF, the as-synthesized US Au NPs@AuZn-MOF hybrids exhibited remarkably promoted electrochemical activity toward the oxidation and sensing of endocrine-disrupting chemical (EDC) estrone. As a result, a highly sensitive electrochemical sensing platform was developed for the detection of estrone in the range of 0.05 μM-5 μM with limit of detection of 12.3 nM (S/N = 3) and sensitivity of 101.3 μA^-1 μM^-1 cm^-2. Considering the structural diversity of MOFs and superior property of ultrasmall Au nanoparticles, the strategy proposed here may open a new avenue for the design and synthesis of other high-activity nanomaterials for electrochemical sensing or other challenging fields.

Ion-biosorption induced core–shell Fe2P@carbon nanoparticles decorated on N, P co-doped carbon materials for the oxygen evolution reaction

This work employs bacteria as precursors and induces a cost-effective biosorption strategy to obtain Fe₂P@carbon nanoparticles decorated on N and P co-doped carbon (Fe₂P@CNPs/NPC) materials.

Cobalt/nitrogen codoped carbon nanosheets derived from catkins as a high performance non-noble metal electrocatalyst for oxygen reduction reaction and hydrogen evolution reaction

Novel energy devices which are capable of alleviating and/or solving the energy dilemma such as overall water splitting and fuel cells require the development of highly efficient catalysts, especially cheap high performance non-precious metal (NPM) catalysts. Here, we prepare highly efficient NPM catalysts of cobalt and nitrogen codoped carbon nanosheets (Co/N-CNSs) for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) using harmful environment-polluting waste of biomass catkins as carbon precursors via a mild mechanical exfoliation and chemical process which is facile, low-cost, environmentally friendly and up-scalable. Compared with a commercial platinum-based catalyst (commercial 20% Pt/C), the Co/N-CNS electrocatalysts show outstanding ORR activity, acceptable HER activity and long term stability with an onset potential of 0.92 V versus the reversible hydrogen electrode (vs. RHE) and a half-wave potential of 0.83 V vs. the RHE in alkaline electrolytes. The excellent performance is closely related to the presence of abundant CoN _x active sites. This work offers a novel and effective approach for preparing highly efficient ORR and HER NPM electrocatalysts from waste biomass materials.

Optimized electronic structure and p-band centre control engineering to enhance surface absorption and inherent conductivity for accelerated hydrogen evolution over a wide pH range

Numerous experiments have demonstrated that an appropriate electronic configuration can effectively activate the electrocatalytic activity. However, systematic studies on the effects of non-metallic elemental doping and its p-orbital center (εp) on electrocatalysis have not yet been carried out. Combining theoretical and experimental methods, we demonstrate an electronic configuration and p-orbital center control engineering for promoting the HER course in both acid and alkaline solutions over group VA elements doped into the inert basal plane of nanoMoS2. In acidic solutions, As-doped MoS2 has the best electrocatalytic activity. Theoretically, the calculated ΔGH of the As atom is only -0.07 eV, indicating that it has excellent catalytic performance. Furthermore, the p-orbital center under and near the Fermi level plays a significant role in the H adsorption course, and the closer the εp value is to the Fermi level, the weaker the H- non-metallic atom bond is. An appropriate εp can insure a proper strength of bond with H and further influence the catalytic activity of the HER. In alkaline solutions, P-doped MoS2 has the best electrocatalytic activity, which is due to the engineering of water dissociation sites by doping P atoms into MoS2 nanosheets. These findings pave the path to develop a rational strategy to trigger the activity of the inert basal plane of MoS2, to enhance the conductivity of inherent MoS2 towards the HER and provide a new idea that can be extended to other layered dichalcogenides.

Transition Metal Phosphide-Based Materials for Efficient Electrochemical Hydrogen Evolution: A Critical Review

As hydrogen has been increasingly considered as promising sustainable energy supply, electrochemical overall water splitting driven by highly efficient non-noble metal electrocatalysts has aroused extensive attention. Transition metal phosphides (TMPs) have demonstrated remarkable electrocatalytic performance, including high activity and robust durability towards hydrogen evolution reaction (HER) in acidic and alkaline as well as neutral electrolytes. In this Review, up-to-date progress of TMP-based HER electrocatalysts is summarized. Various synthesis strategies of TMPs based on selected phosphorus sources are presented, and the reaction mechanisms of HER as well as the contribution of phosphorus in the TMPs to HER activity are briefly discussed. The multiscale approaches for promoting the activity and stability of TMP-based catalysts are discussed with respect to intrinsic electronic structure, hybrids, microstructure, and working electrode interface. Some crucial issues and future perspectives of TMPs are pointed out. These modulated approaches and challenges are also instructive for constructing other high-activity energy-related electrocatalysts.

Hierarchical Porous Molybdenum Carbide Based Nanomaterials for Electrocatalytic Hydrogen Production

The electrocatalytic hydrogen evolution reaction (HER) for the preparation of hydrogen fuel is a very promising technology to solve the shortage of hydrogen storage. However, in practical applications, HER catalysts with excellent performance and moderate price are very rare. Molybdenum carbide (Mo_xC) has attracted extensive attention due to its electronic structure and natural abundance. Here, a comprehensive review of the preparation and performance control of hierarchical porous molybdenum carbide (HP-Mo_xC) based catalysts is summarized. The methods for preparing hierarchical porous materials and the regulation of their HER performance are mainly described. Briefly, the HP-Mo_xC based catalysts were prepared by template method, morphology-conserved transformations method, and secondary conversion method of an organic-inorganic hybrid material. The intrinsic HER kinetics are enhanced by the introduction of a carbon-based support, heteroatom doping, and the construction of a heterostructure. Finally, the future development of HP-Mo_xC based catalysts is prospected in this review.

Recent advancement in the electrocatalytic synthesis of ammonia

Ammonia can not only be used as an active nitrogen component of nitrogen fertilizers, fibers, explosives, etc., but also provides a high energy density and carbon free energy carrier. Currently, ammonia is industrially synthesized by the Haber Bosch process at high temperature and high pressure, which results in high energy loss and a serious greenhouse effect. The electrocatalytic nitrogen reduction reaction (NRR) is a sustainable and environmentally friendly strategy for the synthesis of ammonia. Although lots of electrocatalysts have been developed for this reaction, further breakthroughs are needed in catalytic activity, selectivity and Faraday efficiency to meet the large-scale commercial demand. In this review, the recent advance in NRR electrocatalysis is thoroughly commented on. Different kinds of electrocatalysts used in ammonia synthesis (including single atom catalysts, metal oxide catalysts, nanocomposite catalysts, and metal free catalysts) are introduced. The reaction mechanism of the NRR is discussed in detail. The structure-function relationship and efficient strategies to improve the ammonia yield are clearly discussed. The effect of the electronic structure and morphology of catalysts on the selectivity of the NRR is highlighted. The research directions and perspectives on the further development of more efficient electrocatalysts for the NRR are provided.

Electrochemistry in Carbon-based Quantum Dots

Electrochemistry belongs to an important branch of chemistry that deals with the chemical changes produced by electricity and the production of electricity by chemical changes. Therefore, it can not only act a powerful tool for materials synthesis, but also offer an effective platform for sensing and catalysis. As extraordinary zero-dimensional materials, carbon-based quantum dots (CQDs) have been attracting tremendous attention due to their excellent properties such as good chemical stability, environmental friendliness, nontoxicity and abundant resources. Compared with the traditional methods for the preparation of CQDs, electrochemical (EC) methods offer advantages of simple instrumentation, mild reaction conditions, low cost and mass production. In return, CQDs could provide cost-effective, environmentally friendly, biocompatible, stable and easily-functionalizable probes, modifiers and catalysts for EC sensing. However, no specific review has been presented to systematically summarize both aspects until now. In this review, the EC preparation methods of CQDs are critically discussed focusing on CQDs. We further emphasize the applications of CQDs in EC sensors, electrocatalysis, biofuel cells and EC flexible devices. This review will further the experimental and theoretical understanding of the challenges and future prospective in this field, open new directions on exploring new advanced CQDs in EC to meet the high demands in diverse applications.

Acid-directed morphology control of molybdenum carbide embedded in a nitrogen doped carbon matrix for enhanced electrocatalytic hydrogen evolution

By an acid-directed strategy, β-Mo₂C nanomaterials embedded in a nitrogen doped carbon matrix (β-Mo₂C/NC) with controlled morphology are synthesized and exhibit outstanding HER activities in both acidic and alkaline solutions.

Defect-induced nucleation and epitaxial growth of a MOF-derived hierarchical Mo2C@Co architecture for an efficient hydrogen evolution reaction

The 3D hierarchical structure in catalysts not only the preserves intrinsic characteristics of each component, but also achieves increased specific surface area and active sites for the hydrogen evolution reaction (HER). Herein, we report a new strategy to synthesize efficient 3D hierarchical catalysts composed of Mo₂C nanosheets and Co nanoparticles (H-Mo₂C@Co). It was realized by using raw materials, defect-rich MoO_x, Co(NO₃)₂·6H₂O and 2-methylimidazole, to design Mo/Co bimetallic metal–organic frameworks (BMOFs), followed by pyrolysis at 800 °C. The defects in MoO_x induced preferential nucleation and growth of the BMOFs so that they can ensure the construction of a stable 3D hierarchical structure. Mo₂C and Co have a synergistic effect in improving the HER via providing large surface areas (351.5 m² g⁻¹), more active sites and optimizing charge transfer. It can achieve 10 mA cm⁻² at low overpotential over a wide pH range (144 mV in 0.5 M H₂SO₄ and 103 mV in 1.0 M KOH) and the properties can be well maintained in both acid and alkaline electrolyte after 2000 cycles. The hierarchical catalyst contains no noble metal, can be synthesized on a large scale and recycled by magnetic stirring, demonstrating great potential in water splitting, wastewater treatment, dye adsorption and other fields.

In this work, we report a new strategy to synthesize efficient 3D hierarchical catalysts composed by Mo₂C nanosheets and Co nanoparticles (H-Mo₂C@Co). The Mo₂C and Co makes a synergistic effect in improving HER via providing large surface areas.

Mo-Doped ultrafine VC nanoparticles confined in few-layer graphitic nanocarbon for improved electrocatalytic hydrogen evolution

Developing highly efficient, durable electrocatalysts based on cheap, non-precious metals for the hydrogen evolution reaction (HER) is still the key issue in the field of hydrogen economy.

Recent Advances of Porous Graphene: Synthesis, Functionalization, and Electrochemical Applications

Graphene is a 2D sheet of sp² bonded carbon atoms and tends to aggregate together, due to the strong π-π stacking and van der Waals attraction between different layers. Its unique properties such as a high specific surface area and a fast mass transport rate are severely blocked. To address these issues, various kinds of 2D holey graphene and 3D porous graphene are either self-assembled from graphene layers or fabricated using graphene related materials such as graphene oxide and reduced graphene oxide. Porous graphene not only possesses unique pore structures, but also introduces abundant exposed edges and accelerates mass transfer. The properties and applications of these porous graphenes and their composites/hybrids have been extensively studied in recent years. Herein, recent progress and achievements in synthesis and functionalization of various 2D holey graphene and 3D porous graphene are reviewed. Of special interest, electrochemical applications of porous graphene and its hybrids in the fields of electrochemical sensing, electrocatalysis, and electrochemical energy storage, are highlighted. As the closing remarks, the challenges and opportunities for the future research of porous graphene and its composites are discussed and outlined.

Co Nanoislands Rooted on Co-N-C Nanosheets as Efficient Oxygen Electrocatalyst for Zn-Air Batteries

Developing non-precious-metal bifunctional oxygen reduction and evolution reaction (ORR/OER) catalysts is a major task for promoting the reaction efficiency of Zn-air batteries. Co-based catalysts have been regarded as promising ORR and OER catalysts owing to the multivalence characteristic of cobalt element. Herein, the synthesis of Co nanoislands rooted on Co-N-C nanosheets supported by carbon felts (Co/Co-N-C) is reported. Co nanosheets rooted on the carbon felt derived from electrodeposition are applied as the self-template and cobalt source. The synergistic effect of metal Co islands with OER activity and Co-N-C nanosheets with superior ORR performance leads to good bifuctional catalytic performances. Wavelet transform extended X-ray absorption fine spectroscopy and X-ray photoelectron spectroscopy certify the formation of Co (mainly Co⁰ ) and the Co-N-C (mainly Co²⁺ and Co³⁺ ) structure. As the air-cathode, the assembled aqueous Zn-air battery exhibits a small charge-discharge voltage gap (0.82 V@10 mA cm^-2 ) and high power density of 132 mW cm^-2 , outperforming the commercial Pt/C catalyst. Additionally, the cable flexible rechargeable Zn-air battery exhibits excellent bendable and durability. Density functional theory calculation is combined with operando X-ray absorption spectroscopy to further elucidate the active sites of oxygen reactions at the Co/Co-N-C cathode in Zn-air battery.