Nitrogen-doped Carbon Matrix Research Articles

Facile and green synthesis cobalt embedded in N-doped porous carbon under zeo-waste conditions as an efficient oxygen evolution reduction catalyst

A facile and green method is developed to synthesize cobalt species embedded in a nitrogen-doped carbon matrix (P–Co@NCs). The materials are synthesized using hard template precursors via single-step in-situ thermal treatment under free solvent conditions. The optimal P–Co@NC composite prepared through rational synthesis and synergic composition shows an efficient electrocatalytic performance for oxygen evolution reduction (OER). The P–Co@NC exhibits the OER overpotential of 350 mv at 10 mA cm −2 and low Tafel 73 mv·dec −1 in 0.1 M KOH electrolyte. The advantage of catalyst is the dispersion of Co species, which are in close interaction with nitrogen-doped carbon matrix. The Co-Nx plays a dominating role among Co species in P–Co@NC and is well protected by the nitrogen-doped carbon matrix layer. That resulted in efficient electron transport on CNTs (high conductivity) that improves the OER performance of P–Co@NC compared to the reference catalysts (IrO 2 and B–Co@NC). The P–Co@NC also showed excellent cycling performance from long-term chronoamperometry testing. Interestingly, the P–Co@NC catalyst could be synthesized straightforward via a short solvent-free single-step process that introduced it as a green and environmental friendly method, which can be potential to develop catalyst based on metal embedded N-doped carbon. • The single-step, rapid and effective “green” route of the IST method to synthesize cobalt species embedded in nitrogen-doped carbon (P–Co@NC). • The advantages of economic practicability, minimization of synthesis period, energy consumption without any waste formation could outweigh the catalyst for OER performance. • The advantage of Co dispersion and close interaction with nitrogen-doped carbon matrix showed efficient catalytic performance. • The efficient electron transport on CNTs (high conductivity) improved the OER performance of P–Co@NC over the reference catalysts (IrO 2 and B–Co@NC).

Precise identification of active sites of a high bifunctional performance 3D Co/N-C catalyst in Zinc-air batteries

Developing highly active and robust non-noble metal bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of dominant significance for global applications in rechargeable Metal-air Batteries. Fine-tuning the exposed active sites is a competent way to improve their performance. Herein, the NaCl template-assisted strategy for rationally designing a three-dimensional cellular structured nitrogen-doped carbon matrix integrated with nano-scaled Co species has been developed. The resulting electrocatalyst (3D Co/N-C) exhibits a positive half-wave potential of 0.84 V (vs RHE) in ORR, and a low potential of 1.56 V (vs RHE) at 10 mA cm−2 during OER process. Moreover, 3D Co/N-C based Zn-air Batteries (ZABs) exhibit excellent battery performance, especially remarkable power density. The poisoning experiments and DFT calculations identify active sites as pyridinic N and Co during ORR and OER processes, respectively. This work provides a general and easy-to-perform tactic to design bifunctional catalysts, thus helps precisely modulate effective components for ZABs.

Synergistic Effect between Monodisperse Fe3O4 Nanoparticles and Nitrogen-Doped Carbon Nanosheets to Promote Polysulfide Conversion in Lithium-Sulfur Batteries.

Effective fabrication of electrocatalysts active in anchoring and converting lithium polysulfides is critical for the manufacturing of high-performance lithium-sulfur batteries (LSBs). In this study, original Fe3O4 nanospheres with diameters close to 12 nm were finely dispersed over a porous nitrogen-doped carbon matrix by the freeze-drying method to produce a three-dimensional composite material (nano-Fe3O4/PNC) suitable for application as a sulfur host in LSBs. Nano-Fe3O4/PNC loaded with sulfur (S@nano-Fe3O4/PNC) was used as a cathode in a Li-S cell, whose initial discharge specific capacity reached 1256 mA h g-1 at a 0.1 C rate. After 100 charge-discharge cycles at a 0.2 C rate, the reversible capacity of S@nano-Fe3O4/PNC remained at 745 mA h g-1, demonstrating a capacity retention rate of 70%. Importantly, a high Coulombic efficiency of more than 99% was achieved, indicating effective inhibition of the polysulfides' "shuttle effect" by nano-Fe3O4/PNC. The use of electrolytes containing lithium nitrate further reduces the "shuttle effect" of polysulfides. This study demonstrates the synergistic effect between metal oxide nanoparticles and N-doped carbon, which plays an important role in promoting the adsorption and conversion of polysulfides in LSBs.

Nest-type NCM ⊂ Pt/C with oxygen capture character as advanced electrocatalyst for oxygen reduction reaction

A unique nest-type catalyst has been designed with a nest of oxygen capture surrounding catalytic Pt centers, which shows much promoted performance, on the base of Pt/C catalyst, for oxygen reduction reaction (ORR). The nest is constructed with nitrogen-doped carbon matrix (NCM), derived from the controlled carbonization of PANI precursor, to cover Pt/C catalyst. The unique structure of the catalyst (denoted as NCM ⊂ Pt/C) has many merits. Firstly, it can capture oxygen both in air and in acidic electrolyte. Compared with naked Pt/C, it is found that, in air, the oxygen concentration within the porous nest of NCM surrounding Pt/C particles is ∼13 times higher than atmospheric oxygen concentration and, in acidic electrolyte, the concentration of activated oxygen over the catalyst NCM ⊂ Pt/C rise to ∼1.9 times. Secondly, the NCM nest offers a special electronic modulation on Pt centers toward modified ORR kinetics and then catalytic performances. With these merits, compared with Pt/C, the NCM ⊂ Pt/C catalyst shows 3.2 times higher turnover frequency value and 2.9 times enhanced specific activity for ORR with half-wave potential at 0.894 V. After 50,000 sweeping cycles, the NCM ⊂ Pt/C catalyst retains ∼66% mass activity and still has advantages over the fresh Pt/C catalyst. We envision that the nest-type catalyst provides a new idea for progress of practical Pt/C ORR catalyst.

Ultrasmall metal (Fe, Co, Ni) nanoparticles strengthen silicon oxide embedded nitrogen-doped carbon superstructures for long-cycle-life Li-ion-battery anodes

A universal electrospray-carbonization approach to prepare ternary metal/SiO x /nitrogen-doped carbon (NC) superstructures is proposed, where metal (Fe, Co, Ni, CoNi, FeNi, FeCo and FeCoNi) and small SiO x nanoparticles (NPs) are homogeneously distributed in NC matrix. Metal greatly promotes the electrochemical activity and stability of the SiO x system, which can be considered as high-performance Li-ion-battery anodes. • Metal/SiO x /nitrogen-doped carbon superstructures are designed as LIB anodes. • Nitrogen-doped carbon inhibits the gathering of SiO x and relieves its strain. • Ultrasmall Ni nanoparticles and nitrogen-doped carbon improve the kinetics of SiO x . • The strategy to prepare multiple SiO x - or metal-based composites is universal. For silicon oxides (SiO x ) as a prospective Li-ion-battery anode material, the low inherent conductivity and huge volume fluctuation during cycling immensely limit their electrochemical performance. Herein, a universal electrospray-carbonization approach to prepare ternary metal/SiO x /nitrogen-doped carbon (NC) superstructures is proposed. Accordingly, metal (Fe, Co, Ni, CoNi, FeNi, FeCo and FeCoNi) nanoparticles (NPs) and small SiO x NPs derived from rice husks (RHs) are homogeneously distributed in the NC matrix. Metal (Fe, Co, Ni) NP-embedded NC frameworks avoid the accumulation, increase the conductivity and accommodate adequent volume expansion of SiO x NPs. This results in an enhanced rate capability and excellent cycle stability upon cycling. Besides, Ni/SiO x /NC (NSC) superstructures with ultra-small Ni NPs can exhibit better electrochemical kinetics for fast diffusion of ions and charge transfer and cyclability than Co/SiO x /NC (CSC) and Fe/SiO x /NC (FSC) composites. When NSC superstructures are employed as lithium-ion battery (LIB) anodes, superior specific capacities of 757.5 mA h g −1 at the 200th cycle, as well as superb long cyclability with discharge capacities of 665.0 mA h g −1 for 500 cycles at 500 mA g −1 and 116.3 mA h g −1 at the 5000th cycle, even at 10 A g −1 , are achieved. Furthermore, the easy and general approach for preparing multiple SiO x -, metal- or alloy-based superstructures paves the way for designing high-performance rechargeable batteries and electrocatalysts.

Boosting the energy density of supercapacitors by designing both hollow NiO nanoparticles/nitrogen-doped carbon cathode and nitrogen-doped carbon anode from the same precursor

• The hollow NiO/NC was designed based on the Kirkendall effect. • 2. The pure NC with hollow structure was prepared using the same precursor. • 3. DFT calculations prove that NiO/NC and NC have excellent electrochemical performance. • 4. High-energy–density asymmetric supercapacitor of 40.2 Wh kg −1 was achieved. Designing the transition metal oxide-based electrode with hollow nanostructure is of great importance for high-performance supercapacitors. Here, the hollow NiO encapsulated in a nitrogen-doped carbon matrix (NiO/NC) is synthesized by using the precursor of Ni-based metal–organic complex based on the Kirkendall effect. With the same precursor, the hollow NC is obtained by removing the Ni element through an acid etching method. Density functional theory (DFT) calculations convince that both hollow NiO/NC and NC have high electrical conductivity and adsorption energy for OH – , demonstrating their high practicability for supercapacitor applications. In a three-electrode system, the NiO/NC sample prepared under 700 °C displays a high specific capacitance (1026 F g −1 at 1 A g −1 ) and excellent cycle stability (80.2% capacity retention over 8000 cycles). Importantly, a high energy density of 40.2 Wh kg −1 was achieved based on the asymmetric supercapacitor assembled with NiO/NC cathode and NC anode. This work provides new insights on designing high-performance electrode materials to boost supercapacitor performance using the same precursor.

Co-embedded carbon nanotubes modified N-doped carbon derived from poly(Schiff base) and zeolitic imidazole frameworks as efficient oxygen electrocatalyst towards rechargeable Zn-air battery

Developing nonprecious-metal bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is greatly significant for rechargeable metal-air batteries. In this work, Co nanoparticles encapsulated in nitrogen-doped carbon nanotubes (CNTs) tangled with nitrogen-doped carbon (Co@CNT-NC) has been obtained via a facile in-situ growth-pyrolysis route with the hybrid of zeolitic-imidazole-framework-67 nanoparticles and a triazine-containing poly(Schiff-base). Benefiting from its high surface area (1458 m2 g−1), effective N dopant, interwoven with CNTs and the synergistic effects of Co nanoparticles and nitrogen-doped carbon matrix, the optimized Co@CNT-NC exhibits a superior bifunctional activity with a small potential difference (0.76 V) between OER and ORR. The assembled Co@CNT-NC-based zinc-air battery displays a high power density of 179.3 mW cm−2, a high energy density up to 949 mAh gZn−1 and outstanding long-term durability.

Metal-organic framework derived carbon-supported bimetallic copper-nickel alloy electrocatalysts for highly selective nitrate reduction to ammonia

Developing electrocatalysts for efficient reduction of nitrate contaminant to value-added ammonia as energy carrier is a pivotal part for restoring the nitrogen cycle. However, the selectivity of ammonia is far from satisfaction, often suffering from accumulation of toxic nitrite byproduct. Herein, a series of CuNi alloy nanoparticles embedded in nitrogen-doped carbon matrix (CuNi/NC) with hierarchical pores were fabricated by pyrolysis of bimetallic metal–organic frameworks (MOFs). The catalysts exhibited excellent selectivity (94.4%) and faradaic efficiency (79.6%) for nitrate reduction to ammonia, greatly outperforming the performance of monometallic Cu/NC (selectivity of 60.8% and faradaic efficiency of 60.6%). Impressively, the introduction of nickel distinctly suppressed the production of toxic byproduct of nitrite. Online differential electrochemical mass spectrometry (DEMS) and in situ surface-enhanced infrared absorption spectroscopy (SEIRAS) tests were utilized to reveal the key intermediates and the reaction pathway. Density functional theory (DFT) calculations demonstrated that the introducing of nickel into copper lattice modified both the electronic and geometric structures of the catalysts. The copper and nickel sites in the CuNi alloy catalysts operate synergistically to facilitate the hydrogenation of NO2* to HNO2* and suppress the hydrogen evolution reaction, boosting the selective formation of ammonia. This work could provide a new synthetic route for bimetallic catalysts and mechanistic understanding for nitrate to ammonia reaction.

Precisely Constructing Orbital Coupling-Modulated Dual-Atom Fe Pair Sites for Synergistic CO2 Electroreduction

Electrochemical reduction of CO2 (CO2RR) provides an attractive pathway to achieve a carbon-neutral energy cycle. Single-atom catalysts (SAC) have shown unique potential in heterogeneous catalysis, but their structural simplicity prevents them from breaking linear scaling relationships. In this study, we develop a feasible strategy to precisely construct a series of electrocatalysts featuring well-defined single-atom and dual-site iron anchored on nitrogen-doped carbon matrix (Fe1–N–C and Fe2–N–C). The Fe2–N–C dual-atom electrocatalyst (DAC) achieves enhanced CO Faradaic efficiency above 80% in wider applied potential ranges along with higher turnover frequency (26,637 h–1) and better durability compared to SAC counterparts. Furthermore, based on in-depth experimental and theoretical analysis, the orbital coupling between the iron dual sites decreases the energy gap between antibonding and bonding states in *CO adsorption. This research presents new insights into the structure–performance relationship on CO2RR electrocatalysts at the atomic scale and extends the application of DACs for heterogeneous electrocatalysis and beyond.

Biomass-derived carbon nanosheets coupled with MoO2/Mo2C electrocatalyst for hydrogen evolution reaction

Transition metal carbide such as molybdenum carbide has been widely used in electrolytic water for hydrogen production due to its potential catalytic property. The synthesis of molybdenum carbide-based high-efficient catalysts by simple process remains great challenges. Herein, Mo oxide/carbide material with hybrid morphology was synthesized by carbonizing mixture of lotus roots and Mo salt. The as-obtained material consists of MoO2/Mo2C (MOMC) anchored on biomass-derived nitrogen-doped carbon (NC) matrix. The results show that as-prepared material displays leaf-like and belt-like nanosheets, and the MOMC/NC catalyst with optimal Mo contents exhibits an excellent activity with a low overpotential of 138 mV to drive 10 mA cm−2 and Tafel slope is 56.7 mV dec−1 in alkaline medium, indicating that as-prepared catalyst will have promising application in the field of catalysis.

Regulating the coordination capacity of ATMP using melamine: facile synthesis of cobalt phosphides as bifunctional electrocatalysts for the ORR and HER.

Due to the complexity of the synthetic process of cobalt phosphides (CoP), ongoing efforts concentrate on simplifying the preparation process of CoP. In this work, amino tris(methylene phosphonic acid) (ATMP, L1) and melamine (MA, L2) are assembled into two-dimensional (2D) organic nanostructures by hydrogen bonding and ionic interactions via a supramolecular assembly, which greatly weakens the coordination ability of L1 with Co2+. As the introduced L2 is rich in carbon and nitrogen, it allows the cobalt-organophosphate complex to be placed under a strongly reducing atmosphere during the high-temperature calcination process to achieve an in situ phosphating purpose. The resulting catalyst (N-CoP/NC) exhibits the sought-after enhanced oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) performance. For the ORR in 0.1 M KOH, an enhanced onset potential (0.908 V vs. RHE) and diffusion limiting current (6.280 mA cm-2) can be obtained, which is comparable to those of 20% Pt/C (0.911 V vs. RHE, 5.380 mA cm-2). For the HER in 0.5 M H2SO4, an overpotential of 150 mV is required to drive a current of 10 mA cm-2. Moreover, Density Functional Theory (DFT) calculations reveal the catalytic pathway of N-CoP/NC.

Cobalt nanoparticles embedded in a nitrogen-doped carbon matrix for reductive amination of biomass-derived furfural to furfurylamine

The selective synthesis of furfurylamine (FAM) through reductive amination of biomass-derived furfural was acheived using Co/NC-700 catalyst.

MOF-on-MOF Strategy to Construct a Nitrogen-Doped Carbon-Incorporated CoP@Fe-CoP Core-Shelled Heterostructure for High-Performance Overall Water Splitting.

The design and preparation of efficient and low-cost catalysts for water electrolysis are crucial and highly desirable to produce eco-friendly and sustainable hydrogen fuel. Herein, we prepared nitrogen-doped carbon-incorporated CoP@Fe-CoP core-shelled nanorod arrays grown on Ni foam (CoP@Fe-CoP/NC/NF) through phosphorization of ZIF-67@Co-Fe Prussian blue analogue (ZIF-67@CoFe-PBA). The hierarchical nanorod arrays combined with the core-shelled structure offer favorable mass/electron transport capacity and maximize the active sites, thus enhancing the electrochemically active surface area. The synergistic effect of the bimetallic components and the nitrogen-doped carbon matrix endow the composite with an optimized electronic structure. Benefiting from the above superiorities of morphological and chemical compositions, this self-supported CoP@Fe-CoP/NC/NF heterostructure can drive alkaline hydrogen evolution reaction and oxygen evolution reaction with overpotentials of 97 and 270 mV to yield 100 mA cm-2, respectively. The two-electrode alkaline electrolyzer constructed by this heterostructure shows a low cell voltage of 1.58 V to yield 10 mA cm-2, superior to the precious-metal-based electrocatalyst apparatus (IrO2∥Pt/C). This study offers a feasible and facile approach to develop efficient electrocatalysts for water electrolysis, which applies to other electrochemical energy conversion and storage applications.

Phase-mediated cobalt phosphide with unique core-shell architecture serving as efficient and bifunctional electrocatalyst for hydrogen evolution and oxygen reduction reaction

Hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) have been considered as two critical processes in the field of electrocatalytic water-splitting for hydrogen production and fuel cells. However, the sluggish reaction kinetics of HER and ORR required efficient electrocatalyst such as Pt to promote such process. Transition metal phosphides (TMPs) exhibit great potential to replace noble metal electrocatalysts to accelerate HER and ORR due to their high activity and easy availability. Herein, a highly-efficient bifunctional CoP electrocatalyst for HER and ORR, featuring a unique core-shell structure decorated on nitrogen-doped carbon matrix was designed and constructed via etching a cobalt-based zeolitic imidazolate framework (ZIF-67) with phytic acid (PA) followed by pyrolysis treatment (PA-ZIF-67–900). Experimental results revealed that the pure-phase single-crystalline CoP exhibited outstanding electrocatalytic performance in HER and ORR, superior to Co(PO3)2 in PA-ZIF-67–700, hybrid phase of Co(PO3)2 and CoP in PA-ZIF-67–800 and Co2P-doped CoP in PA-ZIF-67–1000. To reach the current density of 10 mA/cm2 the as-synthesized CoP required an overpotential of 120 mV for HER in 1 mol/L KOH and half-wave potential of 0.85 V in O2-saturated 0.1 mol/L KOH. This work present new clue for construction of efficient and bifunctional electrocatalyst in the field of energy conversion and storage

Nano Silicon Composite with Gelatin/Melamine Derived N-doped Carbon as an Efficient Anode Material for Li-ion Batteries

Silicon (Si) has a high theoretical capacity and low working potential vs. Li/Li<sup>+</sup>, and has been investigated as the most capable negative electrode material for lithium-ion batteries (LIBs). However, Si undergoes significant volume changes during the Li<sup>+ </sup>alloying/ dealloying processes, leading to unstable cycle life and limiting its practical applicability in anodes. Introducing carbon into the Si anodes can effectively address the Si drawbacks, while providing advantages of improved conductivity and structural stability. In this study we choose gelatin/ melamine combination as an eco-friendly and cost-effective source for nitrogendoped carbon to make a Si composite. The prepared composite was studied as an anode material for LIBs, and it delivered excellent cyclability with 2175 mAh g<sup>-1</sup> capacity after 50 cycles with 86% capacity retention at 200 mA g<sup>-1</sup>. The composite exhibited superior rate capability and improved Li<sup>+</sup> diffusion properties compared with bare Si nanoparticles (Si NP). The significant enhancement could be attributed to the structural stability and conductivity provided by the nitrogen-doped carbon matrix. This work promotes emerging batteries with low-cost materials as a promising solution for increasing energy storage requirements.

Cobalt single atom site isolated Pt nanoparticles for efficient ORR and HER in acid media

Hitherto, developing an economical and stable high-activity bifunctional Pt catalyst for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) becomes necessary for fuel cells and regeneration fuel cell system. However, how to uniformly disperse and firmly fix Pt nanoparticles (NPs) on carbon support with optimal particle size for catalysis is still a big challenge. Herein, by taking advantage of the isolating effect of the cobalt (Co) single atom site to Pt, strong interaction between Co single atoms and Pt, and the confinement of the porous carbon matrix derived metal organic frameworks, we successfully evenly immobilize Pt NPs on ZnCo-ZIF originated porous nitrogen-doped carbon matrix with rich cobalt single atoms (Co SAs-ZIF-NC) as multiple active sites. Compared with the commercial Pt/C catalyst, Pt@Co SAs-ZIF-NC, with ultralow Pt loading and ideal particle size, not only increases the active center, but also promotes the catalysis kinetics, greatly improving the ORR and HER catalytic activity. Under acidic conditions, its half-wave potential (0.917 V) is superior to commercial Pt/C (0.868 V), and the mass activity (0.48 A per mgPt) at 0.9 V is 3 times that of Pt/C (0.16 A per mgPt), surpassing the U.S. DOE target of 0.44 A per mgPt. Besides, it also shows outstanding HER performance. At 20 and 30 mV, its mass activity is even 4.5 and 13.6 times that of Pt/C. When further employed for HER in seawater, its mass activity is about 4 times as high as that of Pt/C, demonstrating the great potential applications. By using Co single atom sites in Co SAs-ZIF-NC to isolate Pt, the obtained Pt@Co SAs-ZIF-NC catalyst, with uniform and highly dispersed Pt nanoparticles on porous Co SAs-ZIF-NC, presents highly efficient and stable dual-function catalysis toward oxygen reduction and hydrogen evolution reactions. • Single Co atom sites in Co SAs-ZIF-NC can isolate Pt and own strong interaction with Pt. • Obvious synergistic effect exists between Co single atom sites and Pt NPs in Pt@Co SAs-ZIF-NC catalysts. • With uniform and highly dispersed Pt NPs, Pt@Co SAs-ZIF-NC exhibits greatly enhanced ORR performance in acidic media. • In acidic media and seawater, high HER performance beyond commercial Pt catalysts is also obtained for the catalyst. • It provides a promising method for designing and constructing highly active and stable ultralow Pt-loaded catalysts.

Bi nanorods anchored in N-doped carbon shell as anode for high-performance magnesium ion batteries

The rechargeable magnesium batteries are potentially applicable in large-scale energy storage systems because of the low costs and rich sources. But the alternative anodes for magnesium ion batteries have not been fully developed. In this work, a novel bismuth-carbon composite with bismuth nanorods anchored in nitrogen-doped mesoporous carbon matrix (Bi@NC), was prepared as anode for magnesium ion batteries by carbonizing the dopamine-coated bismuth metal precursors. The matrix facilitated the magnesiation/de-magnesiation of bismuth due to its highly electronic conductive network. Moreover, it restrained the aggregation of bismuth nanorods and serves as a buffer layer to alleviate the mechanical strain of bismuth nanorods upon magnesium insertion/extraction. As the anode for magnesium ion batteries, the Bi@NC core-shell nanorods delivered a reversible capacity of 360 mAh g−1 at the current density of 100 mA g−1, and 87 % of the initial capacity was achieved after 100 cycles. The standout rate performance is 275 mAh g−1 at the current density of 1 A g−1. Such a good electrochemical property demonstrated the great application potential of Bi@NC as anode in magnesium ion batteries.

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.

Nitridation-induced in situ coupling of Ni-Co4N particles in nitrogen-doped carbon nanosheets for hybrid supercapacitors

The self-supported integrated structure of electrode consisting of heteroatoms is advantageous for high-performance energy storage applications. Herein, we developed heteroatomic Ni-Co4N nanoparticles laminated on highly conductive nitrogen-doped carbon (NC) matrix through in-situ nitridation for high energy and stable hybrid supercapacitor (HSC). The plenty of rendering electrochemically active sites, specifically, single-atom Ni, Co4N nanoparticles, and heteroatomic N-doped carbon matrix, and their several synergistic effects facilitate fast electron transfer and superior electrochemical performance. Benefiting from these merits, the resultant Ni-Co4N@NC electrode demonstrates robust electrochemical activity with high specific capacity of 397.5 mA h g−1, high rate capability of 72.4% and superior cycling stability over 10,000 cycles. The heteroatomic Ni-Co4N@NC electrode is further employed for the HSC cell beside with the activated carbon (AC) electrode, which establish the specific energy of 57.2 Wh kg−1 at a specific power of 843.8 W kg−1 and cyclic stability of 89.7% after 15,000 cycles. The present study highlights the utilization of heteroatomic self-supported metal nitrides for the high energy HSCs cell, paving the way to the expansion of highly efficient electrode materials for the future energy storage systems.

Mn-N-C Nanostructure Derived from MnO2-x/PANI as Highly Performing Cathode Additive in Li-S Battery

Highly dispersed Mn metallic nanoparticles (15.87 nm on average) on a nitrogen-doped porous carbon matrix were prepared by thermal treatment of MnO2-x/polyaniline (PANI), which was derived from the in situ polymerization of aniline monomers initiated by γ-MnO2 nanosheets. Owing to the large surface area (1287 m2/g), abundant active sites, nitrogen dopants and highly dispersed Mn sites on graphitic carbon, an impressive specific capacity of 1319.4 mAh g−1 with an admirable rate performance was delivered in a Li-S battery. After 220 cycles at 1 C, 80.6% of the original capacity was retained, exhibiting a good cycling stability.