N-doped carbon shell encapsulated PtZn intermetallic nanoparticles as highly efficient catalysts for fuel cells

Nano Research - The high cost and poor durability of Pt nanoparticles (NPs) have always been great challenges to the commercialization of proton exchange membrane fuel cells (PEMFCs). Pt-based...     

One-step scalable preparation of N-doped nanoporous carbon as a high-performance electrocatalyst for the oxygen reduction reaction

N-doped porous carbon materials have been prepared by a simple one-step pyrolysis of ethylenediaminetetraacetic acid (EDTA) and melamine in the presence of KOH and Co(NO₃)₂·6H₂O. The combination of the high specific area (1485 m²·g^?1), high nitrogen content (10.8%) and suitable graphitic degree results in catalysts exhibiting high activity (with onset and half-wave potentials of 0.88 and 0.79 V vs the reversible hydrogen electrode (RHE), respectively) and four-electron selectivity for the oxygen reduction reaction (ORR) in alkaline medium—comparable to a commercial Pt/C catalyst, but far exceeding Pt/C in stability and durability. Owing to their superb ORR performance, low cost and facile preparation, the catalysts have great potential applications in fuel cells, metal-air batteries, and ORR-related electrochemical industries.      

Facile synthesis of Co-CoO<Subscript>x</Subscript>/N-doped carbon nanotubes hybrids as efficient and bifunctional catalysts for hydrogen and oxygen evolution

Developing low-cost, efficient, and bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is an attractive yet challenging task. Herein, we report a novel, simple and one-pot method to fabricate ultrafinely dispersed Co-CoO_x nanoparticles encapsulated in a nitrogen doped carbon nanotubes (denoted as Co-CoO_x/CN) via an efficient thermal condensation of d-glucosamine hydrochloride, melamine and Co(NO₃)₂·H₂O. A well-designed Co-CoO_x based hybrid that possesses high activity and excellent durability for the OER and HER in alkaline solution has been fabricated. The catalyst displays good stability for 30,000 s and small Tafel slope of 82 mV per decade for OER and 110 mV per decade for HER. Detailed electrochemical and physical studies indicate that the high OER and HER activity of the hybrid catalyst arises from the strong interaction between Co-based NPs and N-doped carbon nanotubes, and especially the synergistic effect of Co and cobalt oxide.     

Graphitizing N-doped mesoporous carbon nanospheres via facile single atom iron growth for highly efficient oxygen reduction reaction

Nano Research - Single atom catalyst is of great importance for the oxygen reduction reaction (ORR). However, facile preparation of single atom catalyst without using well-designed precursors or...     

Rational design of hierarchically porous Fe-N-doped carbon as efficient electrocatalyst for oxygen reduction reaction and Zn-air batteries

The rational design and construction of hierarchically porous nanostructure for oxygen reduction reaction (ORR) electrocatalysts is crucial to facilitate the exposure of accessible active sites and promote the mass/electron transfer under the gas-solid-liquid triple-phase condition. Herein, an ingenious method through the pyrolysis of creative polyvinylimidazole coordination with Zn/Fe salt precursors is developed to fabricate hierarchically porous Fe-N-doped carbon framework as efficient ORR electrocatalyst. The volatilization of Zn species combined with the nanoscale Kirkendall effect of Fe dopants during the pyrolysis build the hierarchical micro-, meso-, and macroporous nanostructure with a high specific surface area (1,586 m²·g⁻¹), which provide sufficient exposed active sites and multiscale mass/charge transport channels. The optimized electrocatalyst exhibits superior ORR activity and robust stability in both alkaline and acidic electrolytes. The Zn-air battery fabricated by such attractive electrocatalyst as air cathode displays a higher peak power density than that of Pt/C-based Zn-air battery, suggesting the great potential of this electrocatalyst for Zn-air batteries.

     

Ketjenblack carbon supported amorphous manganese oxides nanowires as highly efficient electrocatalyst for oxygen reduction reaction in alkaline solutions

A composite air electrode consisting of Ketjenblack carbon (KB) supported amorphous manganese oxide (MnOx) nanowires, synthesized via a polyol method, is highly efficient for the oxygen reduction reaction (ORR) in a Zn-air battery. The low-cost and highly conductive KB in this composite electrode overcomes the limitations due to low electrical conductivity of MnOx while acting as a supporting matrix for the catalyst. The large surface area of the amorphous MnOx nanowires, together with other microscopic features (e.g., high density of surface defects), potentially offers more active sites for oxygen adsorption, thus significantly enhancing ORR activity. In particular, a Zn-air battery based on this composite air electrode exhibits a peak power density of ～190 mW/cm2, which is far superior to those based on a commercial air cathode with Mn3O4 catalysts.     

NiP2/FeP heterostructural nanoflowers interwoven by carbon nanotubes as highly efficient electrocatalyst for oxygen evolution reaction

Oxygen evolution reaction (OER) for water splitting has a sluggish kinetics, thus significantly hindering the reaction efficiency. So far, it is still challenging to develop a cost-efficient and highly active catalyst for OER processes. To address such issues, we design and synthesize NiP₂/FeP heterostructural nanoflowers interwoven by carbon nanotubes (NiP₂/FeP@CNT) by a hydrothermal reaction followed by phosphating. The NiP₂/FeP@CNT catalyst delivers excellent OER performance: it displays an ultralow Tafel slope of 44.0 mV dec^?1 and a relatively low overpotential of 261 mV at 10 mA cm^?2, better than RuO₂ commercial catalyst; it also shows excellent stability without observable decay after 20-h cycling. The outstanding OER property is mainly attributed to its special 3D stereochemical structure of CNT-interwoven NiP₂/FeP heterostructural nanoflowers, which is highly conductive and guarantees considerable active sites. Such nanostructure greatly facilitates the charge transfer, which significantly improves its electrocatalytic activity. This work offers a simple method to synthesize non-precious transition metal-based phosphide electrocatalysts with a unique hierarchical nanostructure for water splitting.

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An oxygen reduction electrocatalyst based on carbon nanotube-graphene complexes

Oxygen reduction reaction catalysts based on precious metals such as platinum or its alloys are routinely used in fuel cells because of their high activity. Carbon-supported materials containing metals such as iron or cobalt as well as nitrogen impurities have been proposed to increase scalability and reduce costs, but these alternatives usually suffer from low activity and/or gradual deactivation during use. Here, we show that few-walled carbon nanotubes, following outer wall exfoliation via oxidation and high-temperature reaction with ammonia, can act as an oxygen reduction reaction electrocatalyst in both acidic and alkaline solutions. Under a unique oxidation condition, the outer walls of the few-walled carbon nanotubes are partially unzipped, creating nanoscale sheets of graphene attached to the inner tubes. The graphene sheets contain extremely small amounts of irons originated from nanotube growth seeds, and nitrogen impurities, which facilitate the formation of catalytic sites and boost the activity of the catalyst, as revealed by atomic-scale microscopy and electron energy loss spectroscopy. Whereas the graphene sheets formed from the unzipped part of the outer wall of the nanotubes are responsible for the catalytic activity, the inner walls remain intact and retain their electrical conductivity, which facilitates charge transport during electrocatalysis.     

MoS2/Co9S8/MoC heterostructure connected by carbon nanotubes as electrocatalyst for efficient hydrogen evolution reaction

High-performance multifunctional materials for water splitting driven by low voltage are crucial for hydrogen evolution reaction (HER),but developing such materials is challenging.Herein,a simple strategy was designed to build a MoS2/Co9S8/MoC@CNT-N (MCM@CNT-N) heterostructure with a large number of interfaces.Regarding the HER,the synthesized MCM@CNT-N heterostructure catalyst showed high efficiency and stable electrocatalytic performance,with a low overpotential of 174.2 mV and a small Tafel slope of 84.7 mV dec-1 at a current density of 10 mAcm-2 in 0.5 M H2SO4.In addition to the function of heterojunctions,the excellent activity is also attributed to the introduction of Co and N atoms and the formation of carbon nanotubes.This work provides a new approach to build efficient and low-cost electrocatalysts for electrochemical reactions.     

过渡金属和磷共掺杂多孔碳作为氧气还原电催化剂

碳基材料作为非贵金属催化剂具有导电性能高、稳定性能好、价格低廉、环境友好等优点,在燃料电池阴极催化剂领域中引起了广泛的关注,尤其是过渡金属和异原子共掺杂能够显著提高碳材料的氧气还原催化活性。本文采用聚醚(F127)作为软模版,苯酚、甲醛作为碳源,四苯基溴化膦作为磷源,硝酸盐作为过渡金属来源,通过挥发溶剂自组装及高温煅烧过程制备了过渡金属(Co、Fe、Ni、Mn)和磷(P)共掺杂多孔碳材料(TM-P-C)。通过旋转环盘电极研究了TM-P-C在0.1 mol/L KOH电解液中的氧气还原电催化性能。研究结果表明：TM-P-C催化剂具有较高的氧化还原反应(ORR)电催化性能,其ORR活性为P-Co-C>P-NiC>P-Fe-C>P-Mn-C,其中P-Co-C的ORR电催化性能可与商业20wt%Pt/C催化剂相媲美,其电流密度与20wt%Pt/C催化剂的电流密度相当,与20wt%Pt/C仅存在66 mV的半波电位差,表现为ORR的4e–转移途径。制备的TM-P-C催化剂所具有的较高氧气还原电催化活性主要来自于过渡金属和P原子之间的协同作用。此外,TM-P-C催化剂表现出优异的...     

High N-doped hierarchical porous carbon networks with expanded interlayers for efficient sodium storage

Sodium-ion batteries (SIBs) have been attracting considerable attention as a promising candidate for large-scale energy storage because of the abundance and low-cost of sodium resources. However, lack of appropriate anode materials impedes further applications. Herein, a novel self-template strategy is designed to synthesize uniform flowerlike N-doped hierarchical porous carbon networks (NHPCN) with high content of N (15.31 at.%) assembled by ultrathin nanosheets via a self-synthesized single precursor and subsequent thermal annealing. Relying on the synergetic coordination of benzimidazole and 2-methylimidazole with metal ions to produce a flowerlike network, a self-formed single precursor can be harvested. Due to the structural and compositional advantages, including the high N doping, the expanded interlayer spacing, the ultrathin two-dimensional nano-sized subunits, and the three-dimensional porous network structure, these unique NHPCN flowers deliver ultrahigh reversible capacities of 453.7 mAh·g⁻¹ at 0.1 A·g⁻¹ and 242.5 mAh·g⁻¹ at 1 A·g⁻¹ for 2,500 cycles with exceptional rate capability of 5 A·g⁻¹ with reversible capacities of 201.2 mAh·g⁻¹. The greatly improved sodium storage performance of NHPCN confirms the importance of reasonable engineering and synthesis of hierarchical carbon with unique structures.

     

N-doped carbon nanocages: Bifunctional electrocatalysts for the oxygen reduction and evolution reactions

Highly efficient metal-free, carbon-based, bi-functional electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) have attracted increased attention for use in electrochemical energy conversion systems, owing to their low cost and high activity. In this work, N-doped carbon nanocages (N-CCs) with a porous self-supported architecture and high specific surface area are synthesized by a facile interfacial assembly synthetic route. The materials are comprehensively characterized by scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption experiments, X-ray diffraction, and X-ray photoelectron spectroscopy. Cyclic voltammetry, chronoamperometry, and linear sweep voltammetry demonstrate that the as-prepared N-CC could serve as an effective metal-free electrocatalyst with excellent catalytic activity, long-term operation durability, and excellent methanol tolerance for the ORR in alkaline media. In the presence of 3 mM methanol, the half wave potential of the N-CCs for the ORR is 190 mV; this is more positive than that of the commercial Pt/C electrocatalyst. Meanwhile, the N-CCs also show an OER activity comparable to that of the commercial Ru/C electrocatalyst, revealing their bifunctional property.

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F-doped carbon hollow nanospheres for efficient electrochemical oxygen reduction

Journal of Materials Science - Herein, a metal-free catalyst F-CHNS-900 has been prepared through a one-step pyrolysis of polytetrafluoroethylene and ZnCl2 at 900&nbsp;°C. According to the...     

Multi-scale regulation in S,N co-incorporated carbon encapsulated Fe-doped Co9S8 achieving efficient water oxidation with low overpotential

Sulfide compounds provide a type of promising alternative for oxygen evolution reaction(OER)electrocatalysts due to their diversity,intrinsic activities,low-price and earth-abundance.However,the unsmooth mass transport channel,the collapse of the structure and insufficient intrinsic activities limit their potential for OER performance.In respond,the dense Fe-doped Co₉S₈ nanoparticles encapsulated by S,N co-incorporated carbon nanosheets(Fe-Co₉S₈@SNC)were proposed and synthesized via fast thermal treatment from ultrathin metal-organic frameworks(MOFs)nanosheets.In designed catalysts,the nanosheet configuration connected by nanoparticles retained rich access for permeation of electrolyte and precipitation of O₂ bubbles during OER process.Meanwhile,the outer carbon layer of Co9S8 provided additional catalytic activity while acting as armor to keep the structure stability.At the atomic scale,the doped Fe regulated the local charge density and the d-band center for facilitating desorption of oxygen intermediates.Benefiting from this multi-scale regulation strategy,the Fe-Co₉S₈@SNC displays an ultralow overpotential of 273 mV at 10 mA·cm^-2 and small Tafel slope of 55.8 mV·dec^-1,which is even close to the benchmark RuO₂ catalyst.This concept could provide valuable insights into the design of other catalysts for OER and beyond.