Facile synthesis of Ni-free CoFe2O4 nanoparticles on ordered mesoporous carbon as electrocatalysts for oxygen reduction reaction

Nanoporous carbons derived from metal-conjugated phosphoprotein/silica: Efficient electrocatalysts for oxygen reduction and hydrazine oxidation reactions

SummaryEfficient electrocatalyst toward hydrogen evolution/oxidation reactions (HER/HOR) and oxygen reduction reaction (ORR) is desirable for water splitting, fuel cells, etc. Herein, we report an advanced platinum phosphide (PtP2) material with only 3.5 wt % Pt loading embedded in phosphorus and nitrogen dual-doped carbon (PNC) layer (PtP2@PNC). The obtained catalyst exhibits robust HER, HOR, and ORR performance. For the HER, a much low overpotential of 8 mV is required to achieve the current density of 10 mA cm−2 compared with Pt/C (22 mV). For the HOR, its mass activity (MA) at an overpotential of 40 mV is 2.3-fold over that of the Pt/C catalyst. Interestingly, PtP2@PNC also shows exceptional ORR MA which is 2.6 times higher than that of Pt/C and has robust stability in alkaline solutions. Undoubtedly, this work reveals that PtP2@PNC can be employed as nanocatalysts with an impressive catalytic activity and stability for broad applications in electrocatalysis.

Today, the development of active and stable catalysts still represents a challenge to be overcome in the research field of low-temperature fuel cells.[...]

Highly stable and methanol tolerant oxygen reduction reaction electrocatalyst Co/CoO/SnO@N-C nanocubes by one-step introduction of functional components

With the dramatically increased market demands of new energy materials due to the development of a large number of electronic devices and environmental awareness of the awakening, catalysts for oxygen reduction reaction (ORR) which are the most critical parts for high energy capacity and cleaning power sources including fuel cells and metal-air batteries have attracted highly attention and intense researches recently. Despite massive efforts, developing catalysts of high efficiency, long-term durability and excellent methanol tolerance with low cost for ORR is still a big challenge. Pt and Pt–based alloys are still the best choices for catalyzing oxygen reduction process by now. However, their high cost, low abundance, inferior stability and declining activity hinder their large-scale uses in industry. Therefore, selecting alternative materials to replace Pt and improve its performance is of great concern. Chitosan, as the second most abundant biopolymer in nature, is rich in the outer shell of some arthropod (prawns, crabs, insects) and the inner shell and cartilage of mollusks (squid, cuttlefish) with some attractive properties, such as non-toxic, biocompatibility and safety, especially, its natural nitrogen rich, strong chelation effects, sustainable and environmental friendly and low cost depend that it can be heavy used to synthesize metal and nitrogen co-doped carbon (MNC) nanomaterials , which can provide an enhanced catalytic activities. In the present work, taking advantage of strong chelation effects between hydroxyl group and metal ions and abundant natural nitrogen of chitosan, we developed a novel Co and N co-doped carbon (Co-N-C) nanocomposites as high performance electrocatalysts for ORR by using a simple and facile hydrothermal method, followed by high-temperature calcination at inert gas atmosphere. This material shows a delectable catalytic activity compared to the commercial 20% Pt/C electrode in the alkaline solution for ORR with a relative positive onset potential of -0.045V (vs. Hg/HgO), a much improved by 16.7% current density than Pt/C (loading ~ 0.4mg/cm2) as well as excellent durability performance and superior methanol tolerance. In addition, the method we used in this research is also suitable for preparing other MNC, which demonstrates that we found a new, straightforward and low-cost way to synthesis a series of catalysts for ORR which are comparable to commercial Pt/C. Cyclic voltammetry (CV) was employed to test the ORR catalytic activity of Co-N-C-800 and the commercial 20% Pt/C catalyst in saturated O2 alkaline solution (0.1 M KOH) and shown in Figure 1a, an obvious cathodic peak can be found at -0.10 V vs. Hg/HgO which implies excellent ORR performance, and according to figure 1b, we can find that our Co-N-C-800 has a very close onset potential (-0.045V) and much higher current density (16.7% improved) in comparison to that of the commercial Pt/C, respectively, superior to the performances of pure chitosan without Co (C-800), which can confirm that Co-doping is crucial to the outstanding activity performance of Co-N-C-800. Owning to small metal nanocrystals of cobalt can improve the conductivity of materials and charge transfer efficiency between carbon and cobalt and give more active sites1. RDE measurements at various rotating speeds at a scan rate of 10 mV s-1 in O2-saturated solution were carried out for Co-N-C-800 and shown in Figure 1c. The current density shows a typical increase with rotation rate due to the shortened diffusion layer and the linearity of K-L plots for Co-N-C-800 indicates a good four-electron reaction path selectivity with the electron transfer numbers (n) is ≈ 3.9, which is close to that of Pt/C catalyst and further demonstrates an outstanding catalytic performance of this catalyst. Acknowledgments This work was financially supported by the Shenzhen Peacock Plan (KQCX20140522150815065), the Natural Science Foundation of Shenzhen (JCYJ20150331101823677) and the Science and Technology Innovation Foundation for the Undergraduates of SUSTC (2015x19 and 2015x12). Reference 1. Xie, S.; Huang, S.; Wei, W.; Yang, X.; Liu, Y.; Lu, X.; Tong, Y., Chitosan Waste-Derived Co and N Co-doped Carbon Electrocatalyst for Efficient Oxygen Reduction Reaction. ChemElectroChem 2015, 2 (11), 1806-1812. Figure 1

Development of cheap, abundant and metal-free N-doped carbon materials as high efficiency oxygen reduction electrocatalysts is crucial for their practical applications in future fuel cell devices. Here, three-dimensional (3D) N-doped porous carbon (NPC) materials have been successfully developed by a simple template-assisted (e.g., SiO2 spheres) high temperature pyrolysis approach using shrimp-shell derived N-doped carbon nanodots (N-CNs) as carbon and nitrogen sources obtained through a facile hydrothermal method. The shrimp-shell derived N-CNs with a product yield of ∼ 5% possess rich surface O- and N-containing functional groups and small nanodot sizes of 1.5-5.0 nm, which are mixed with surface acidification treated SiO2 spheres with an average diameter of ∼ 200 nm in aqueous solution to form a N-CNs@SiO2 composite subjected to a thermal evaporation treatment. The resultant N-CNs@SiO2 composite is further thermally treated in a N2 atmosphere at different pyrolysis temperatures, followed by acid etching, to obtain 3D N-doped porous carbon (NPC) materials. As electrocatalysts for oxygen reduction reaction (ORR) in alkaline media, the experimental results demonstrate that 3D NPC obtained at 800 °C (NPC-800) with a surface area of 360.2 m(2) g(-1) exhibits the best ORR catalytic activity with an onset potential of -0.06 V, a half wave potential of -0.21 V and a large limiting current density of 5.3 mA cm(-2) (at -0.4 V, vs. Ag/AgCl) among all NPC materials investigated, comparable to that of the commercial Pt/C catalyst with an onset potential of -0.03 V, a half wave potential of -0.17 V and a limiting current density of 5.5 mA cm(-2) at -0.4 V. Such a 3D porous carbon ORR electrocatalyst also displays superior durability and high methanol tolerance in alkaline media, apparently better than the commercial Pt/C catalyst. The findings of this work would be valuable for the development of low-cost and abundant N-doped carbon materials from biomass as high performance metal-free electrocatalysts.

The design of non-precious electrocatalysts with low-cost, good stability, and an improved oxygen reduction reaction(ORR) to replace the platinium-based electrocatalyst is significant for application of fuel cells and metal-air batteries with high energy density. In this study, we synthesize iron-carbide(Fe3C) embedded nitrogen(N) doped carbon nanofiber(CNF) as electrocatalysts for ORRs using electrospinning, precursor deposition, and carbonization. To optimize electrochemical performance, we study the three stages according to different amounts of iron precursor. Among them, Fe3C-embedded N doped CNF-1 exhibits the most improved electrochemical performance with a high onset potential of −0.18 V, a high E1/2 of −0.29 V, and a nearly four-electron pathway (n = 3.77). In addition, Fe3C-embedded N doped CNF-1 displays exellent long-term stabillity with the lowest ΔE1/2= 8 mV compared to the other electrocatalysts. The improved electrochemical properties are attributed to synergestic effect of N-doping and well-dispersed iron carbide embedded in CNF. Consequently, Fe3C-embedded N doped CNF is a promising candidate for non-precious electrocatalysts for high-performance ORRs.

Tri(Fe/N/F)-doped mesoporous carbons as efficient electrocatalysts for the oxygen reduction reaction

Enhancement of selectivity towards the synthesis of hydrogen peroxide by dimensional effect in mesoporous carbon

A novel sulfur-nitrogen dual doped ordered mesoporous carbon electrocatalyst for efficient oxygen reduction reaction

CuO modified ZnO on nitrogen-doped carbon: a durable and efficient electrocatalyst for oxygen reduction reaction

Three-dimensional nanocomposites derived from combined metal organic frameworks doped with Ce, La, and Cu as a bifunctional electrocatalyst for supercapacitors and oxygen reduction reaction

Carbon material is a promising electrocatalyst for the oxygen reduction reaction (ORR). Doping of heteroatoms, the most widely used modulating strategy, has attracted many efforts in the past decade. Despite all this, the catalytic activity of heteroatoms-modulated carbon is hard to compare to that of metal-based electrocatalysts. Here, a "double-catalysts" (Fe salt, H3 BO3 ) strategy is presented to directionally fabricate porous structure of crystal graphene nanoribbons (GNs)/amorphous carbon doped by pyridinic NB pairs. The porous structure and GNs accelerate ion/mass and electron transport, respectively. The N percentage in pyridinic NB pairs accounts for ≈80% of all N species. The pyridinic NB pair drives the ORR via an almost 4e- transfer pathway with a half-wave potential (0.812 V vs reversible hydrogen electrode (RHE)) and onset potential (0.876 V vs RHE) in the alkaline solution. The ORR catalytic performance of the as-prepared carbon catalysts approximates commercial Pt/C and outperforms most prior carbon-based catalysts. The assembled Zn-air battery exhibits a high peak power density of 94 mW cm-2 . Density functional theory simulation reveals that the pyridinic NB pair possesses the highest catalytic activity among all the potential configurations, due to the highest charge density at C active sites neighboring B, which enhances the interaction strength with the intermediates in the p-band center.

Fe3C nanoparticle decorated Fe/N doped graphene for efficient oxygen reduction reaction electrocatalysis

Heteroatom-doped carbon materials, particularly carbons co-doped with single atomic transition metals (e.g. Fe) and nitrogen, have emerged as one of the most competitive non-precious electrocatalysts for the cathodic oxygen reduction reaction (ORR) in proton-exchange-membrane fuel cells to replace precious platinum (Pt) catalyst. Most carbon-based non-precious electrocatalysts, however, were built on conventional carbon materials such as activated carbon and more recently metal-organic-framework-derived carbon, both of which feature essential drawbacks of carbon corrosion and low electron conductivity due to their low extent of graphitization.1-2 We report here the direct synthesis of well-defined CNTs co-doped with a high density of Fe-Nx active sites (denoted as Fe-N/CNT) through a solid-phase catalytic growth approach, where Fe precursor catalyzed the growth of CNTs from melamine sponge precursor under NH3 atmosphere and simultaneously doped in-situ into the CNT walls with nitrogen. The atomic structure and electrocatalytic properties of the Fe-N/CNT electrocatalysts were characterized by aberration-corrected scanning transmission electron microcopy, Mößbauer spectroscopy, electrochemical analysis and density functional theory calculations. We further design and synthesis a hierarchical Fe-N/CNT electrocatalyst where primary Fe-N/CNTs are enwrapped with secondary Fe-N/CNTs in order to increase the proportion of the Fe-N/CNT active site. The optimized Fe-N/CNT catalyst featured with a high degree of graphitization and high density of Fe-Nx catalytic sites, demonstrating both high ORR activity and remarkable stability in both half-cell test and a single hydrogen fuel cell membrane-electrode-assembly test. Reference: [1] Lefevre M, Proietti E., Jaouen F., Dodelet J. Iron-based catalysts with improved oxygen reduction activity in polymer electrolyte fuel cells. Science, 324, 71-74 (2009). [2] Chen, YJ. Ji SF., Wang D.S., Li Y.D., Angew Chem Int Ed, 56, 6937-6941 (2017) [3] Xia D.S., Wang R.Z., Wei Y.P., Gan L., Kang F.Y. Melamine-sponge-derived non-precious fuel cell electrocatalyst with hierarchical pores and tunable nitrogen chemical states for exceptional oxygen reduction reaction activity. Materials Today Energy, 9, 271-278 (2018)