Nitrogen-doped Carbon Shell Research Articles

Nitrogen-doped carbon shell armored ‘Janus’ Co/Co9S8 heterojunction as robust bi-functional oxygen reduction reaction/oxygen evolution reaction catalysts in seawater-based rechargeable Zn-air batteries

It is of paramount importance to develop highly efficient and Cl−corrosion-resistant bi-functional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) for application in seawater-based Zn-air batteries (S-ZABs), but the process remains full of challenges. Herein, a facile and effective strategy was adopted to fabricate the N-doped carbon shell armored ‘Janus’ Co/Co9S8 heterojunction catalyst (denoted as Co/Co9S8-NMC). The well-defined ‘Janus’ structure endows the catalyst with a ‘synergistic effect’ between Co and Co9S8 species, which can also accelerate the electron transfer via ‘Janus’ interfaces, thus boosting ORR/OER performance. Besides, N-doped carbon shells can be considered armor for protecting the catalyst from Cl− corrosion. By virtue of these merits, the resulting Co/Co9S8-NMC catalyst exhibits excellent catalytic activity for ORR and OER in seawater electrolyte, accompanied by a half-wave potential of 0.83 V and a low overpotential of 298 mV to achieve a current density of 10 mA/cm2. Besides, the S-ZABs based on the Co/Co9S8-NMC catalyst deliver a high maximum power density of 162.29 mW/cm2 and robust stability over 600 h. This work advances the development of highly efficient bi-functional catalysts for S-ZABs.

Preparation of hollow core-shelled MnCoSex/MnO@nitrogen-doped carbon composite by multiple interfaces coupling and its electrochemical properties

Hollow MnCoSex/MnO nanospheres wrapped with nitrogen-doped carbon shell (MnCoSex/MnO@N-C) were prepared via a simple solvothermal and selenization strategy followed by the carbon coating procedure. Benefitting from the multiple interfaces coupling between MnCoSex and MnO and unique hollow core-shell architecture, MnCoSex/MnO@N-C composites possess high specific capacitance and superior rate capability, even at a high current density of 5 A/g, the MnCoSex/MnO@N-C can operate steadily for 20000 cycles with 84.6% of initial specific capacitance maintained. An asymmetric supercapacitor device assembled by MnCoSex/MnO@N-C and active carbon depicts a high energy density of 11.2 W·h/kg at a power density of 810 W/kg and a long cycle life with 84.0% of the initial specific capacitance retained after 20000 cycles.

Control of the metal-support interactions in Ru on N-doped graphene-encapsulated Ni nanoparticles to promote their hydrogen evolution reaction catalytic performance

Controlling metal-support interaction (MSI) is considered as an effective strategy to optimize the electronic structure of catalysts and thus promote their catalytic performance. Here, with the strong MSI by both metal core and nitrogen-doped carbon shell, the synthesized Ru supported on N-doped graphene-encapsulated Ni nanoparticles (Ni@NC/Ru) show excellent performance towards hydrogen evolution reaction (HER). It exhibits a very low HER potential of 28 mV at the current density of 10 mA cm−2, and high durability that the potential only increases approximately 7 mV after 10,000 cyclic voltammetry cycles. The high HER performance is attributed to the strong MSI from the tuning effect of Ni metal core and N-dope graphene shell, which optimizes the hydrogen binding energy of the catalysts. This study may shed light on the rational design of superior HER catalysts.

Protection Against Absorption Passivation on Platinum by a Nitrogen-Doped Carbon Shell for Enhanced Oxygen Reduction Reaction.

In polymer electrolyte type fuel cells, the platinum-based catalysts are applied for the oxygen reduction reaction. However, the specific adsorption from the sulfo group in perfluorosulfonic acid ionomers has been considered to passivate the active sites of the platinum. Herein, we present platinum catalysts covered by an ultrathin two-dimensional nitrogen-doped carbon shell (CNx) layer to protect the platinum from the specific adsorption of perfluorosulfonic acid ionomers. Such coated catalysts were obtained by the facile polydopamine coating method, which is available to tune the thickness of the carbon shell by tuning the polymerization time. The coated catalysts that possess a CNx with a thickness of 1.5 nm demonstrated superior ORR activity and comparable oxygen diffusivity when compared to the commercial Pt/C. These results were supported by the changes in the electronic statements observed in the X-ray photoelectron spectroscopy (XPS) and CO stripping analyses. Furthermore, the oxygen coverage, CO displacement charge, and operando X-ray absorption spectroscopy (XAS) tests were employed to identify the protection effect of CNx in coated catalysts compared with the Pt/C catalysts. In summary, the CNx could not only suppress the oxide species generation but also prevent the specific adsorption of the sulfo group in the ionomer.

Bimetallic selenide nanocages covered by carbon layer deliver high rate performance for sodium ion storage

Sodium-ion batteries (SIBs) have been acknowledged as a particularly promising supplement to lithium-ion batteries, thanks to the abundant sodium resources, geographically-wide distribution and low cost. However, the large volume expansion hence poor structural stability of the anode in the Na+ insertion/deinsertion process severely compromises the rate performance of SIBs. Herein, we report the hierarchical, hollow structured nanocages of nickel-cobalt bimetallic selenide covered by nitrogen-doped carbon shell (NiCo3Se4@NC) as anode material for SIB. The hollow structure and the abundant holes on the cage walls greatly shorten the transfer distance for Na+ ions and buffer the volume expansion during the Na+ storage process. The bimetallic form expands the lattice spacing meanwhile increase the density of states near Fermi level. Moreover, the highly-conductive NC shell further benefits the charge transfer and structural stability upon Na+ storage, and promotes the cycle stability. As a result, surface-responsive capacitive-dominated kinetic process is revealed from the NiCo3Se4@NC anode, delivering a high reversible capacity of 416 mAh/g−1 at a current density of 0.05 A/g−1 and 314 mAh/g−1 at 2 A/g−1. This work proposes an efficient strategy to substantially increase the rate performance and cycle stability of SIBs.

Hollow CuSbSy Coated by Nitrogen-Doped Carbon as Anode Electrode for High-Performance Potassium-Ion Storage

As a potential anode material for potassium-ion batteries (PIBs), bimetallic sulfides are favored by researchers for their high specific capacity, low cost, and long cycle life. However, the non-ideal diffusion rate and poor cycle stability pose significant challenges in practical applications. In this work, bimetallic sulfide CuSbSy@C with a yolk-shell structure was synthesized by in situ precipitation and carbonization. When CuSbSy is applied in the anode of PIBs, it can provide the desired capacity and reduce the volume expansion of the compound through the synergistic effect between copper and antimony. At the same time, the existence of the nitrogen-doped carbon shell confines the material within the shell while improving its electrical conductivity, inhibiting its volume expansion and aggregation. Therefore, CuSbSy@C exhibits a satisfactory capacity (438.8 mAh g−1 at 100 mA g−1 after 60 cycles) and an excellent long cycle life (174.5 mAh g−1 at 1000 mA g−1 after 1000 cycles).

Ultrathin Nitrogen‐Doped Carbon Encapsulated Ni Nanoparticles for Highly Efficient Electrochemical CO2 Reduction and Aqueous Zn‐CO2 Batteries

Electrochemical CO2 reduction reaction (CO2 RR), powered by renewable electricity, has attracted great attention for producing high value-added fuels and chemicals, as well as feasibly mitigating CO2 emission problem. Here, this work reports a facile hard template strategy to prepare the Ni@N-C catalyst with core-shell structure, where nickel nanoparticles (Ni NPs) are encapsulated by thin nitrogen-doped carbon shells (N-C shells). The Ni@N-C catalyst has demonstrated a promising industrial current density of 236.7mA cm-2 with the superb FECO of 97% at -1.1V versusRHE. Moreover, Ni@N-C can drive the reversible Zn-CO2 battery with the largest power density of 1.64mW cm-2 , and endure a tough cycling durability. These excellent performances are ascribed to the synergistic effect of Ni@N-C that Ni NPs can regulate the electronic microenvironment of N-doped carbon shells, which favor to enhance the CO2 adsorption capacity and the electron transfer capacity. Density functional theory calculations prove that the binding configuration of N-C located on the top of Ni slabs (Top-Ni@N-C) is the most thermodynamically stable and possess a lowest thermodynamic barrier for the formation of COOH* and the desorption of CO. This work may pioneer a new method on seeking high-efficiency and worthwhile electrocatalysts for CO2 RR and Zn-CO2 battery.

MOFs-derived hierarchical porous carbon supported Co@NC nanocapsules for pH universal oxygen reduction reaction and Zn-air batteries

The rational design and construction of the hierarchical porous structure of carbon framework to support transition metal-based catalysts is critical to increase their active sites density and facilitate mass/electron transport. Herein, we report a novel nanocapsules with cobalt core and nitrogen-doped carbon shells (Co@NC) supported on MOFs-derived hierarchical porous carbon framework. The rational hierarchical porous carbon framework with controllable size and micropore/mesoporous ratio was achieved by one-step pyrolysis of Zn(acac)2·phen ligand and ZIF-67 precursor, which is beneficial for the mass transport in the oxygen reduction reaction (ORR). The 0.4Co@NC-900 electrocatalyst display a distinguished ORR activity in the pH-universal range, with a half-wave potential of 0.91 V in alkaline and 0.76 V in acid electrolytes. The excellent ORR performance of our electrocatalyst can be attributed to its optimized micropore/mesoporous ratio of carbon framework with efficient mass transport, together with the graphitized carbon shell on Co nanoparticles which not only enhances the electron/proton transport, but also suppresses the chemical corrosion of the Co nanoparticles. Impressively, the Zinc-air battery as air electrode offers peak power density of 203 mW cm−2 and long-term stability of 130 h, showing an excellent battery performance. This study offers a fresh method of constructing ORR catalysts with increased activity and durability over a universal pH range.

Boosting polysulfide confinement and redox kinetics via ZnSe/NC@rGO as separator modifier for high-performance lithium-sulfur batteries

Although lithium-sulfur (Li-S) batteries have an unparalleled specific capacity, the notorious shuttle effect, and slow reaction kinetics severely inhibit their development. Herein, a composite composed of ZnSe nanoparticles with a nitrogen-doped (N-doped) carbon shell uniformly dispersed in reduced graphene oxide (ZnSe/NC@rGO) is designed as a separator modifier for Li-S batteries. The underlying mechanism of the ZnSe/NC@rGO modified separator is confirmed by both systemic electrochemical characterization and density functional theory (DFT) calculations. Graphene as a highly conductive skeleton promotes electrical conductivity, while N-doping provides additional adsorption sites for the immobilization of lithium polysulfides (LiPSs). Moreover, the polar ZnSe has good chemical adsorption capabilities for LiPSs and could lower the decomposition energy barrier of Li2S, which effectively facilitates the catalytic conversion of polysulfides. In addition, the separator modifier is beneficial to the uniform deposition of lithium. Thus, the delicate catalyst can effectively suppress the shuttle effect and accelerate the redox reaction kinetics during the charging and discharging processes. When used as a separator modifier of Li-S batteries, ZnSe/NC@rGO delivers enhanced electrochemical performance, including a high capacity (1057 mAh g–1 at 0.2 C after 100 cycles) and excellent rate performance of 685 mAh g–1 at 3 C. The negligible capacity decay per cycle within 900 cycles at 1 C is as low as 0.043%. These findings not only provide a feasible method for boosting the electrochemical performance of Li-S batteries but also reveal that transition metal selenides have potential in energy storage as electrocatalysts.

ZIF-67-derived porous nitrogen-doped carbon shell encapsulates photovoltaic silicon cutting waste as anode in high-performance lithium-ion batteries

The rapid development of the photovoltaic industry generates nearly 35 wt% micron-scale silicon powder waste in the form of a paste. This study reports the in-situ synthesis of ZIF-67 on the surface of low-cost silicon cutting waste. Submicron-scale porous cage-like silicon-based composites were obtained by carbonization. This hollow framework structure facilitated the large volume expansion/contraction of Si during charging/discharging. The porous nitrogen-doped carbon layer not only yielded rapid transport channels for Li+ and electrons but also improved the electrical conductivity of the material. In addition, the excellent pseudocapacitive performance of the Si@NC-ZIF composite also enhanced lithium storage. The composite exhibited excellent capacity retention of 1623.05 mAh/g after 100 cycles at 200 mA g−1, with the retention rate reaching 86.29 %. When the current was switched from 2000 to 100 mA g−1, the discharge capacity recovered to 1453.35 mAh/g, showing excellent rate performance. This study provides a new approach for the recycling and value-added utilization of photovoltaic silicon cutting waste in lithium-ion battery anodes.

Oriented tuning yolk-shell structure for well-confinement and constructing durability of silicon/carbon composite

Silicon-based materials have been recognized as one of the most promising anode materials for next-generation lithium-ion batteries (LIBs) due to its high theoretical specific capacity (4200 mA h g−1), appropriate lithiation potential and abundance in earth. However, the fulsome volume swell and intrinsically low conductivity result in the sluggish kinetics and the limited cycle life, which severely hinders its commercial application. Herein, a composite of Si@hollow nitrogen-doped carbon (Si@HNC) with typical yolk-shell structure is designed and fabricated via a facile strategy coupled super-molecular self-assembly with carbonization. Benefiting from the buffering effect of yolk-shell nanostructure on the volumetric variation, and the excellent conductivity of the porous nitrogen-doped carbon shell, Si@HNC anode material exhibits high structural stability, fast charge and ion transfer. As a result, the Si@HNC sample with the Si content of 54.4 wt% delivers a reversible capacity of 865 mA h g−1 with the retention of ∼98 % at 1.0 A g−1 after 300 cycles. More surprisingly, a stable capacity of 1013 mA h g−1/3.24 mAh cm−2 is also retained at 0.5 A g−1 after 400 cycles even under the high areal loading of 3.2 mg cm−2.

General synthesis of carbon-guarded cobalt-based nanospheres for oxygen reduction electrocatalysis

We construct carbon-guarded cobalt-based nanospheres composed of metal nanoparticles encased in a nitrogen doped carbon shell (M@NC NP), as efficient ORR catalysts.

Amine-assisted synthesis of the Ni3Fe alloy encapsulated in nitrogen-doped carbon for high-performance water splitting

We synthesized nitrogen-doped carbon shell encapsulated Ni3Fe alloy catalyst (Ni3Fe-NC/NF) for high-performance water splitting. It exhibits low overpotentials for the OER and HER at a high current density, along with ultralong stability.

Preparation of FeCo/C-N and FeNi/C-N Nanocomposites from Acrylamide Co-Crystallizates and Their Use as Lubricant Additives.

FeCo and FeNi nanoalloy particles encapsulated in a nitrogen-doped carbonized shell (FeCo/C-N and FeNi/C-N) were synthesized by thermolysis at 400 °C of polyacrylamide complexes after frontal polymerization of co-crystallizate of Fe and Co or Ni nitrates and acrylamide. During the thermolysis of polyacrylamide complexes in a self-generated atmosphere, Co(II) or Ni(II) and Fe(III) cations are reduced to form FeCo and FeNi nanoalloy particles, while polyacrylamide simultaneously forms a nitrogen-doped carbon shell layer. This unique architecture provides high chemical and thermal stability of the resulting nanocomposites. The average crystallite size of FeCo and FeNi nanoparticles is 10 and 12 nm, respectively. The nanocomposites were studied by X-ray diffraction, atomic force microscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The nanocomposites have been tested as antifriction and antiwear additives in lubricating oils. The optimal concentrations of nanoparticles were determined, at which the antifriction and antiwear properties of the lubricant manifest themselves in the best possible way.

Core-shell-structured CoS2@N-doped carbon nanoneedle array as an efficient bifunctional electrocatalyst for overall water splitting

The development of environmentally friendly and highly effective electrocatalysts was crucial for boosting overall water splitting. Herein, a core-shell structured CoS2@N-doped carbon nanoneedle array grown on Ni foam (CoS2@N-ASC@NF) was directly constructed by a hydrothermal, soaking, and vacuum sulfurization approach. The representative core-shell structure constructed with large ECSA and small interfacial electron transfer resistance benefited the CoS2@N-ASC@NF to display improved electrocatalytic performance. The CoS2@N-ASC@NF displayed electrocatalytic activity toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in a 1.0 M KOH with low overpotentials of 165.6 and 179.4 mV at 10 mA cm−2, respectively. Notably, the assembled electrolytic cell CoS2@N-ASC@NF||CoS2@N-ASC@NF showed low potentials of 1.430 and 1.646 V at 10 and 50 mA cm−2, respectively, which were better than those of RuO2||Pt/C (1.588 V at 10 mA cm−2 and 1.766 V at 50 mA cm−2), and also exhibited exceptional durability for 50 h continuous operation,. The synergism of core-shell structure, uniform nanoneedle array morphology and nitrogen doped carbon shell provided fast diffusion path for electrolyte ions, reduced the interfacial resistance and protect the core from corrosion to boost overall water splitting of CoS2@N-ASC@NF. This work provided us with a new insight into the design of carbon coated transition metal disulfide with good electrocatalytic activity and durability as bifunctional electrocatalyst in the fields of clean and sustainable energy.

Inhibition of Ionomer Specific Adsorption on Pt/C Catalysts Coated with Dopamine-Derived Nitrogen-Doped Carbon

Among the hydrogen-based energy conversion devices, the proton exchange membrane fuel cell (PEMFC) has shown some advantages in high conversion efficiency, no polluted gas generation, and low-temperature operation, which made it possible to be applied in many fields[1]. To date, Pt/C catalysts are still regarded as one the most promising catalysts for the PEMFC. However, for the real application of platinum, the activity will be influenced by the operation environment, like the specific adsorption of the sulfo group in the Nafion ionomer, which is critical to applying the Pt/C as practical electrocatalysts in PEMFC[2]. Recently, the two-dimensional material overlayers like nitrogen-doped carbon shells have shown the function to tune the electronic statement of the metal surface, which was considered to originate from the strong p-d coupling between the doped nitrogen and the platinum nanoparticles and could optimize the O binding energy to improve the activity[3]. In this research, the nitrogen-doped carbon-coated platinum (PTCN) was synthesized by facile thermal treatment from the polydopamine to carbon shells with tunable thickness. To measure the electronic statement change on the catalysts modified with Nafion ionomer during the oxygen reduction reaction (ORR), the Operando X-ray absorption spectroscopy (XAS) was applied at BL36XU in Spring-8.After being coated with the nitrogen-doped carbon shell, the specific activity of PTCN increased by 1.3 times higher than commercial Pt/C catalysts, which could be originated from the interaction between the nitrogen-doped carbon shell and the platinum surface atom. It could be identified by the changes after coated with a nitrogen-doped carbon shell from the X-ray photoelectron spectroscopy (XPS) and XAS N K-edge results. To explore the protective effect of nitrogen-doped carbon shell against the specific adsorption by Nafion ionomer, different amount of ionomer was modified onto the Pt/C and PTCN catalysts, of which the specific activity showed a 16 % decay on Pt/C, however, almost no changes on PTCN. To illustrate this protection effect, the CO displacement charge test was applied to quantitatively analyze the adsorbed species coverage on the platinum surface, and increased coverage of anion species was observed on the higher amount of ionomer additive for Pt/C, however, it showed slight changes on PTCN varying different ionomer content, which suggested the sulfo-group from ionomer could hardly be absorbed on the platinum surface after coated with nitrogen-doped carbon shell. Furthermore, since the CO will get oxidation on the platinum surface from 0.6 V (vs. RHE), the Operando XAS was applied to measure the electronic statement and structure changes during the reaction potential range (0.5 V – 1.1 V vs. RHE). It also showed less change on the 5d vacancy for PTCN. These results showed potential for using carbon-coated catalysts in solving the specific adsorption problem from Nafion ionomer and promoting the large-scale application for the PEMFCs. Figure 1. Influence of the I/C ratio on the specific activity of Pt/C and PTCN at 0.90 V vs RHE. Acknowledgement This work was supported by the project (JPNP20003) and a NEDO FC-Platform project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). And China Scholarship Council (CSC) was acknowledged for the doctoral scholarship of Yunfei Gao (202006270046). Reference s : 1. Debe, M. K. Nature 2012, 486 (7401), 43-51.2. Kodama, K.; Nagai, T.; Kuwaki, A.; Jinnouchi, R.; Morimoto, Y., Nature Nanotech . 2021, 16 (2), 140-147.3. Gan, T.; Yang, J.; Morris, D.; Chu, X.; Zhang, P.; Zhang, W.; Zou, Y.; Yan, W.; Wei, S.-H.; Liu, G., Commun. 2021, 12 (1), 2741. Figure 1

Exploring the Function of Nitrogen-Doped Carbon Shell on Ordered and Disordered PtCo Alloy Catalysts in Oxygen Reduction Reaction By X-Ray Absorption Spectroscopy

The development of proton exchange membrane fuel cells (PEMFCs) has received increasing attention for its potential to get rid of dependence on fossil fuels and curb carbon emissions[1]. However, the application of PEMFC has been limited by the consumption of platinum due to the sluggish kinetics of the cathode reaction and limiting platinum reserves. So far, forming Pt-M (M = non-precious metal) alloying phase catalysts has been regarded as an efficient method to improve the activity and decrease the cost of platinum. However, the introduction of the non-precious metal content will decrease the stability of the catalysts by accelerating the dissolution of metal atoms and agglomeration of the nanoparticles[2]. In this research, the nitrogen-doped carbon coating structure was applied to protect the PtCo nanoparticles. And both ordered (I-PtCo@CNx) and disordered (D-PtCo@CNx) PtCo alloy phase core was synthesized to further explore the role of nitrogen-doped carbon shell in improving the activity and stability. To study the electronic statement and structure changes of the catalysts, both in-situ and ex-situ X-ray absorption spectroscopy (XAS) was applied at BL36XU at SPring-8.The synthesis of order PtCo catalysts, generally, requires a high temperature to overcome the energy barrier of forming the ordering phase, which will cause severe Ostwald ripening and get larger nanoparticles[3]. However, in the participation of nitrogen-doped carbon shells, the particle size could be limited to less than 5 nm. The I-PtCo@CNx exhibited high mass activity and specific activity at 1.08 A mgPt -1 and 1.51 mA cmPt -2, respectively. The XAS and X-ray photoelectron spectroscopy (XPS) analysis showed the decreased electronic density on the I-PtCo@CNx compared with I-PtCo catalysts, which suggested the increase of the activity might be originated from the interaction from the nitrogen-doped carbon shell. Furthermore, the accelerate durability tests (ADTs) were applied to measure the stability of the catalysts. In the rotating disk electrode and fuel cell condition, after 30,000 cycles ADTs, the activity of I-PtCo@CNx showed less decrease compared with other samples. The EXAFS analysis confirmed the high stability of I-PtCo@CNx might come from the less oxygen species generation during the ADTs, especially for the Co, and the confined structure benefits to maintaining the structure. In addition, the operando XAS analysis of the membrane electrode assemblies (MEA) samples also showed the high stability of I-PtCo@CNx after polarization at 1.1 V for 1 h. Figure 1. The Pt L3 edge and Co K edge FT-EXAFS spectra of disordered-PtCo, ordered-PtCo, and ordered-PtCo@CNx in different ADTs cycles at 80 °C in MEA operation condition. Acknowledgement This work was supported by the project (JPNP20003) and a NEDO FC-Platform project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). And China Scholarship Council (CSC) was acknowledged for the doctoral scholarship of Yunfei Gao (202006270046). Reference s : [1] Zhao L.; Zhu J.; Zheng Y.; Xiao M.; Gao R.; Zhang Z.; et al. Adv. Energy Mater. 2022, 12, 2102665.[2] Sun Y.; Polani S.; Luo F.; Ott S.; Strasser P.; Dionigi F. Nat. Commun. 2021, 12 (1), 5984.[3] Yang C.; Wang L.; Yin P.; Liu J.; Chen M.; Yan Q.; et al. Science 2021, 374 (6566), 459-64. Figure 1

Ordered PtCo Intermetallics Featuring Nitrogen‐Doped Carbon Prepared by Surface Coating Strategy for Oxygen Reduction Reaction

AbstractImproving the activity and stability of Pt‐based electrocatalysts is essential for large‐scale commercial applications of fuel cells. The ordered Pt‐based alloy nanomaterials encapsulated by coating have attracted significant attention. Here, we displayed a surface coating strategy to synthesize structurally ordered PtCo alloy catalysts featuring nitrogen‐doped carbon (NC). Experimental results reveal that the sample with appropriate dopamine feeding content shows enhanced oxygen reduction activity and stability, which exhibits a mass activity of 1.36 mA ⋅ mg−1Pt and specific activity of 1.98 mA ⋅ cm−2, superior to those of excessive or low dopamine adding content samples and commercial Pt/C catalyst. The enhanced electrocatalytic performance of this catalyst was attributed to the combined effect including the protection of suitable thickness NC shells, strong electronic interaction and high ordering degree. In this work, the surface coating strategy provides available references to further improve the oxygen reduction performance of PtM alloy catalysts.

Trimetallic Nanoalloy of NiFeCo Embedded in Phosphidated Nitrogen Doped Carbon Catalyst for Efficient Electro-Oxidation of Kraft Lignin

Recently, electro-oxidation of kraft lignin has been reported as a prominent electrochemical reaction to generate hydrogen at lower overpotential in alkaline water electrolysis. However, this reaction is highly limited by the low performance of existing electrocatalysts. Herein, we report a novel yet effective catalyst that comprises nonprecious trimetallic (Ni, Fe, and Co) nanoalloy as a core in a phosphidated nitrogen-doped carbon shell (referred to as sample P-NiFeCo/NC) for efficient electro-oxidation of kraft lignin at different temperatures in alkaline medium. The as-synthesized catalyst electro-oxidizes lignin only at 0.2 V versus Hg/HgO, which is almost three times less positive potential than in the conventional oxygen evolution reaction (0.59 V versus Hg/HgO) at 6.4 mA/cm2 in 1 M KOH. The catalyst demonstrates a turnover frequency (TOF) three to five times greater in lignin containing 1 M KOH than that of pure 1 M KOH. More importantly, the catalyst P-NiFeCo/NC shows theoretical hydrogen production of about 0.37 μmoles/min in the presence of lignin, much higher than that in pure 1 M KOH (0.0078 μ moles/min). Thus, this work verifies the benefit of the NiFeCo nanoalloy incorporated in carbon matrix, providing the way to realize a highly active catalyst for the electro-oxidation of kraft lignin.

Supported Ni0@C[sbnd]N catalyst with dual-reaction surfaces: Structure-performance relation in the selective hydrogenation of p-chloronitrobenzene

How to break the activity-selectivity dependence in halonitrobenzene hydrogenation remains a challenge. In this work, Ni@CN/SiO2 were synthesized and examined in the hydrogenation of p-chloronitrobenzene. It showed that the electron transferred from nitrogen doped carbon shell to Ni0 core (core–shell synergistic effect) dominated the intrinsic activities of Ni@CN/SiO2 with dual-reaction surfaces (H2 dissociated on Ni0 core, while p-chloronitrobenzene was hydrogenated on carbon shell) in the thiophene-free hydrogenation, leading to their higher turnover frequencies than Raney Ni catalyst. During the thiophene-involved hydrogenation, the adsorption of thiophene on Ni0 changed its electron density and blocked the active sites. These enhanced the selectivity, but significantly reduced the activity for Raney Ni catalyst. Comparatively, the carbon shell protected Ni0 core from thiophene adsorption so that the hydrogen dissociated on Ni0 as usual. However, the adsorption of thiophene on the carbon shell reduced the available sites for p-chloronitrobenzene adsorption. Although Ni@CN/SiO2 had lower activities in the thiophene-involved reactions than those of thiophene-free reactions, they achieved ∼100 % p-chloroaniline selectivities and 8-fold higher turnover frequencies than Raney Ni, breaking the activity-selectivity dependence. This reveals that the available sites on the carbon shell and the core–shell synergistic effect determine the thiophene-involved hydrogenation activities of Ni@CN/SiO2 catalysts.