CNT Catalyst Research Articles

The characterization and sodium borohydride electrooxidation of novel carbon nanotube supported copromoted Pd as anode catalyst for fuel cell

AbstractIn the present study, the effect of Co addition on Pd is investigated. Pd/CNT and PdCo/CNT catalysts are prepared via the sodium borohydride (SBH, NaBH4) reduction method. The X‐ray diffraction, transmission electron microscope, and inductively coupled plasma‐mass spectrometry analyses are performed to characterize the PdCo(70‐30)/CNT catalyst. These characterization results reveal that Pd/CNT and PdCo/CNT catalysts are prepared successfully. NaBH4 electrooxidation activities of PdCo/CNT catalysts are examined with electrochemical methods such as cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. PdCo(70‐30)/CNT catalyst has 11.52 mA/cm2 specific activity, 477.18 m2/g electrochemical active surface area, and the best electrochemical stability. Pd is a promising catalyst for NaBH4 electrooxidation reaction.

Carbon nanotube‐based titanium‐ and zirconium‐doped [M–N4] type ORR catalysts. First principle study

AbstractThe efficiency of the Ti‐ and Zr‐doped nitrogen‐codoped carbon nanomaterials based on the (6,6)armchair carbon nanotube C120H24 with incorporated MN4 fragment has been analyzed using the first principle method at the DFT theory level. Two active sites on the catalyst surface have been revealed: the MN4 site and the adjacent NC═CN double bond (C2 site) of the support. A distinctive feature of Ti and Zr metals is that the MN4 site remains active even in the oxidized forms, although the C2 site becomes competitive. The free energy diagrams of the ORR were plotted for associative and dissociative mechanisms for both the initial and different oxidized forms in the acidic and alkaline media. The intermediates corresponding to the global minima were determined depending on the applied electrode potential and on the nature of the metal. Slightly lower exothermicity of oxygen adsorption and lower‐lying intermediates of the same type for Ti metal are indicative of some advantage of the Ti‐doped over the Zr‐doped MN4–CNT catalysts.

Effect of Sn content on Pt/CNT electrocatalysts for direct ethanol fuel cell application

AbstractSeveral bimetallic PtSn catalysts supported on multiwalled carbon nanotubes for ethanol electro‐oxidation were prepared by conventional impregnation‐reduction method. The Pt loading was kept at 20 wt.% and Pt:Sn atomic ratios of 5:1, 3:1, and 1:1 were selected. The catalysts were structurally characterized by temperature programmed reduction, X‐ray diffraction, X‐ray photoelectron spectroscopy, H2 chemisorption, cyclohexane dehydrogenation reaction, and transmission electron microscopy. The electrochemical characterization of the electrocatalytic materials was carried out in acid medium by cyclic voltammetry, linear sweep voltammetry, chronoamperometry, and CO stripping techniques. Among the different stoichiometries tested, the Pt(20)Sn(12.17)/CNT catalyst exhibited the highest electrocatalytic activity for ethanol oxidation reaction, with mass current density of 189.5 mA mgPt−1 at 796 mV (vs. Ag/AgCl).

Highly efficient methanol oxidation reaction on durable Co9S8 @N, S-doped CNT catalyst for methanol fuel cell applications

The implementation of direct methanol fuel cells is seen as a reliable factor in the future energy mix. Efficient energy conversion from methanol requires an active and durable catalyst to drive the anodic methanol oxidation reaction (MOR) in direct methanol fuel cells. As an alternative to high cost noble metals, cobalt-based electrocatalysts are considered potential replacements that meet the high activity and long-term stability for MOR. Herein, we report the preparation of hierarchical Co9S8 nanowires trapped in N-doped carbon nanotubes (N,S–Co@CNT) derived from melamine showing high activity for MOR in alkaline medium. In order to identify the main active sites, we synthesized cobalt particles embedded in carbon structures in absence of a sulphur source (Co@CNT) and evaluated its performance for MOR. The material characterization shows that adding sulphur during pyrolysis enhances the surface area, pore size and lattice defect. In addition, the morphology changes from hemi-spherical particles to nanowires, that significantly improves the electrochemical properties. The current density of N,S–Co@CNT is exceptionally higher (5.5 times) and the onset potential of MOR is shifted to lower potential when compared to Co@CNT. The enhanced activity, durability and stability of N,S–Co@CNT is ascribed to the unique hierarchical structure and surface properties.

Ultrafast fabrication of robust electrocatalyst having Fe/Fe3C and CuNC for enhanced oxygen reduction reaction activity

The search for ultrafast and simple methods to fabricate non-noble metal catalysts to boost electrocatalytic oxygen reduction reaction (ORR) is still ongoing. Herein, we demonstrate a one-step microwave-assisted heating method to prepare copper nitride/iron/iron carbide nanoparticle hybrids (CuNC/Fe/Fe3C/CNT). This ultrafast heating method induces plentiful carbon-wrapped metal and Fe3C nanoparticles that are attached to the surface of CNT and scattered nanosheets. The CuNC/Fe/Fe3C/CNT exhibit a half-wave potential (E1/2) of 0.886 V toward the ORR in alkaline solution, with 220 mV more positive E1/2 than that of CuNC/CNT and Fe/Fe3C/CNT respectively. The activity of as-prepared catalysts is discussed by investigating their structures and compositions and their relationship with the ORR performance. Detailed analysis results disclose that the high activity of the CuNC/Fe/Fe3C/CNT catalysts could be attributed to the interaction of CuNC and Fe/Fe3C species. To be specific, as the electron donor, Fe/Fe3C nanoparticles induce electron localization and promote the formation of Cu (δ + )–NC (0 < δ < 2), therefore leading to the improvement of the ORR performance. This work may offer an ultrafast way to construct efficient catalysts with enhanced ORR performance.

Synthesis of N-doped Co@C/CNT materials based on ZIF-67 and their electrocatalytic performance for oxygen reduction

ZIF-67/CNT materials are prepared by using in situ growth method with cobalt nitrate and 2-methylimidazole (2-MI) as raw materials, polyvinyl pyrrolidone (PVP) as complexing agents. A series of N-Co@C/CNT catalysts are prepared through heating ZIF-67/CNT in N2 atmosphere. The effects of additional proportion of CNT on the catalytic performance of N-Co@C/CNT catalysts for oxygen reduction reaction (ORR) are studied. The chemical states of the materials, micro-morphology, elemental composition, and crystalline structure are analyzed by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), and X-ray diffraction (XRD). The results show that polyhedral ZIF-67 has grown on the surfaces of CNTs. After heat treatment, ZIF-67/CNT transforms to N-Co@C/CNT. The particle size of Co is 10–20 nm. N-Co@C/CNT-2.6 shows the best catalytic performance for ORR in alkaline solution with the onset potential of 0.94 V, half-wave-potential of 0.83 V, and limiting diffusion current density of 5.6 mA cm−2. The ORR on N-Co@C/CNT proceeds through a four-electron path and the yield of H2O2 is 12%, which is close to Pt/C. N-Co@C/CNT shows higher methanol-tolerant ability than Pt/C. The addition of CNT makes N-Co@C expose more active sites. CNT plays an important role in connecting different N-Co@C particles and enhancing the electron conductivity. The contents of graphitic nitrogen and pyridine nitrogen in N-Co@C/CNT-2.6 catalysts are 15.8% and 38.6%, respectively, which are higher than those in N-Co@C (7% and 34%).

Mechanisms of oxygen reduction reaction on B doped FeN 4 G and FeN 4 CNT catalysts for proton‐exchange membrane fuel cells

Density functional theory (DFT) was used to calculate the stability, oxygen reduction reaction (ORR) mechanism and activity of B-doped FeN4CNT (carbon nano-tube [CNT]) and FeN4G (G, graphene). The B-doped catalysts are more stable and active than that of the un-doped, especially for FeN4B2G and FeN4B2CNT. Based on the Mulliken charge and electrostatic potential surface of these catalysts, Fe atom is found to be the most active site for the adsorption of O-contained species. It is shown that their adsorption energies decrease in the range: O > OH > Co-ad OH > OOH > O2 > H2O > H2O2 on these catalysts. H2O2 will be directly dissociated into two co-adsorbed OH* or O* + H2O* instead of H2O2 on the graphene series catalysts, and the process of reaction (H2O2 + * → 2OH*) on the active sites of the CNT series catalysts is strongly exothermic. Hence, desorption of H2O2* into the solution is difficult to proceed during the oxygen reduction process. All the catalysts are expected to promote a single site four electron process through the reaction path of I (O2 → O2* → OOH* → O* → OH* → H2O) except for the catalyst of FeN4CNT. The rate-determining step (RDS) for ORR process on FeN4B2G is the first reduction step (O2* → OOH*), while the RDS is the fourth reduction step (OH* → H2O) for the other catalysts. FeN4B2G exhibits the largest on-set potentials of 0.53 V, which is larger than the on-set potential of un-doped B FeN4G catalyst (0.39 V). In addition, the B-doped FeN4CNT catalyst shows the better activity compared to the un-doped ones.

Electro-catalytic oxidation of HMF to FDCA over RuO2/MnO2/CNT catalysts in base-free solution

Up to 72% yield of 2,5-furandicarboxylic acid was achieved in a neutral electrolyte through the electro-oxidation of 5-hydroxymethylfurfural over a ruthenium–manganese mixed oxide catalyst.

Fe2P encapsulated in carbon nanowalls decorated with well-dispersed Fe3C nanodots for efficient hydrogen evolution and oxygen reduction reactions.

The development of cost-effective, high-efficiency bifunctional electrocatalysts as alternatives to the state-of-the-art Pt-based materials toward the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) is of great significance but still challenging. Herein, an advanced bifunctional electrocatalyst is presented, composed of Fe2P encapsulated in carbon nanowalls decorated with well-dispersed Fe3C nanodots (denoted as Fe2P@Fe3C/CNTs), which is achieved by a novel "inside-out" gas-solid reaction protocol. When functioning as a cathodic catalyst for water splitting, the Fe2P@Fe3C/CNT catalyst needs an ultralow overpotential of 83 mV to deliver a current density of 10 mA cm-2, shows a small Tafel slope of 53 mV dec-1 and ensures long-term stability for over 200 h in an alkaline electrolyte. Notably, the Fe2P@Fe3C/CNT catalyst exhibits an extremely impressive ORR performance with an onset potential (Eonset) of 1.060 V and a half-wave potential (E1/2) of 0.930 V, excellent stability (≈94% activity retention after 36 000 s), and a strong methanol resistance ability, even far outperforming commercial Pt/C (Eonset = 0.955 V, E1/2 = 0.825 V, ≈75% activity retention after less than 3500 s). Such outstanding HER and ORR performances are mainly ascribed to the improved corrosion resistance of the unique Fe2P@C core-shell structures, the abundant catalytically active sites of ultrasmall Fe3C nanodots incorporated in carbon nanowalls, and the good electrical conductivity of 2D graphitic carbon nanotubes used as a support.

All carbon hybrid N-doped carbon dots/carbon nanotube structures as an efficient catalyst for the oxygen reduction reaction.

This paper reports the facile and scalable synthesis of hybrid N-doped carbon quantum dots/multi-walled carbon nanotube (CD/CNT) composites, which are efficient alternative catalysts for the oxygen reduction reaction (ORR) in fuel cells. The N-doped CDs for large-scale production were obtained within 5 minutes via a one-step polyol process using ethylenediamine (ED) in the presence of hydrogen peroxide as an oxidizing agent. For comparison, different CDs were also prepared using ethylene glycol (EG) and ethanolamine (EA) in the same manner. Physicochemical characterization suggested the successful formation of a CD(ED)/CNT hybrid without individual CD(ED)s and CNTs. The N-doped CD(ED)/CNT catalyst exhibited excellent electrocatalytic activity in an alkaline solution compared to other composites (CD(EG)/CNT and CD(EA)/CNT). The Tafel slope (−60.9 mV dec−1) and durability (∼9.1% decay over 10 h) for CD(ED)/CNT were superior to high-performance Pt/C catalysts. The electrochemical double-layer capacitance on the CD(ED)/CNT hybrid showed apparent improvement of the active surface area because of N-doping and highly decorated CDs on the CNT wall. These results provide an innovative approach for the potential application of all carbon hybrid structures in electrocatalysis.

Gram-scale synthesis of single-atom metal-N-CNT catalysts for highly efficient CO2 electroreduction.

Single-atom catalysts (SACs) have attracted much interest for electrochemical CO2 reduction because of their high metal utilization and excellent catalytic activity. However, the practical applications of SACs were restricted by the low production yield. Herein, we developed a facile synthetic strategy for fabricating metal-nitrogen-carbon nanotube (M-N-CNT, M = Ni, Co, Cu, Fe, Mn, Zn, Pt, or Ru) SACs at scale (>1 g) by direct pyrolysis of metal cations, phenanthroline and CNTs at high temperature. The pyrolysis leads to forming coordinated Ni-N active sites anchored on CNTs. The prepared Ni-N-CNT catalyst with a remarkable Ni loading of 2 wt% determined by ICP exhibits the highest activity for CO2-to-CO conversion with a high faradaic efficiency of 94% and excellent stability. Aberration-corrected high-angle annular dark-field transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy confirm the presence of isolated Ni single atoms in Ni-N-CNT, which act as the active centers for CO2 electroreduction while the CNT support offers fast pathways for electron and mass transports. This work laid foundations for future practical applications in CO2 electroreduction, oxygen reduction reactions, water splitting and nitrogen reduction and beyond.

Iron Nanoparticles Embedded in Carbon Nanotubes for Reversible Li-CO2 Batteries

As a main reason of greenhouse effect, CO2 emission should be reduced to alleviate further environmental pollution such as global warming and climate changes.[1] Considering wide and substantial utilization of fossil fuels in various industries, it is hard to diminish the emission in a short time. To handle the problems, carbon capture and storage (CCS) technologies have emerged as new breakthrough of relieving the amount of CO2 in atmosphere, fixing and storing the gaseous CO2 to solid phases.[2] Li-CO2 batteries as electrochemical CCS technology have been spotlighted for their bi-functional applications enabling both energy storage system and environment-friendly CO2 fixation.[3] The Li-CO2 batteries operate with CO2 (Mw. CO2: 44) as a cathode material, which is two-fold lighter than transition metal (e.g. Mw. LiCoO2: 98) in Li-ion batteries, indicating distinguished energy potentials. However, insulating discharge products and inactive reactions of the Li-CO2 cells during cycling lead to cell degradation, showing poor cyclability and low efficiency. Therefore, to utilize the Li-CO2 batteries as next-generation energy storage system, various catalysts should be introduced, facilitating the discharge/charge reaction.In both economic and eco-friendly respects, using bio-waste as a precursor has attracted the attention in the field of catalyst development.[4] Hemoglobin obtained from blood-wastes (such as slaughter and medical wastes) has been introduced as a cathode catalyst.[5-6] It is composed of four globular protein chains each with a Fe-centered porphyrin called heme, which is capable of changing their oxidation numbers. With redox reactions of centered iron, hemoglobin can bind with CO2, interacting directly with the cell reaction in Li-CO2 batteries. Furthermore, various cation (e.g. iron) and anion (e.g. oxygen, nitrogen, and carbon) resources in hemoglobin can be employed as catalytic components. Diverse treatments and procedures can be performed to maximize catalytic effects of hemoglobin-derived catalyst.In this presentation, we introduce a new method, applying capillary action of hemoglobin precursor into CNT, to fabricate Fe nanoparticles embedded in N-doped CNT (Fe NPs@N-CNT) catalysts. By simple treatments, we successfully synthesized Fe NPs@N-CNT and examined the morphological and structural characteristics of the catalyst. The pore size of CNT provides strong force of capillary motion to draw the precursor solution into the tubes and subsequent segregation of Fe components are achieved, showing crystalline structure in TEM analysis. We performed the electrochemical cell tests, employing Fe NPs@N-CNT catalysts, and confirmed the catalytic activities of reduced charge overpotential and enhanced capacity in both discharge and charge process. The utilization of bio-waste as the catalysts provides environmental merits for developing eco-friendly Li-CO2 batteries and moreover, the novel application of capillary motion to fabricate Fe NPs@N-CNT catalysts offers new pathway to develop various catalytic materials.[1] A. M. Appel, J. E. Bercaw, A. B. Bocarsly, H. Dobbek, D. L. DuBois, M. Dupuis, J. G. Ferry, E. Fujita, R. Hille and P. J. Kenis, Chemical reviews, 2013, 113, 6621-6658.[2] N. MacDowell, N. Florin, A. Buchard, J. Hallett, A. Galindo, G. Jackson, C. S. Adjiman, C. K. Williams, N. Shah and P. Fennell, Energy & Environmental Science, 2010, 3, 1645-1669.[3] Y. Qiao, J. Yi, S. C. Wu, Y. Liu, S. X. Yang, P. He and H. S. Zhou, Joule, 2017, 1, 359-370.[4] Z. Ma, K. Wang, Y. Qiu, X. Liu, C. Cao, Y. Feng and P. Hu, Energy, 2018, 143, 43-55.[5] W.-H. Ryu, F. S. Gittleson, J. M. Thomsen, J. Li, M. J. Schwab, G. W. Brudvig and A. D. Taylor, Nature communications, 2016, 7, 1-10.[6] J.-Y. Lee, H.-S. Kim, J.-S. Lee, C.-J. Park and W.-H. Ryu, ACS Sustainable Chemistry & Engineering, 2019, 7, 16151-16159.

Anthraquinone Covalently Modified Carbon Nanotubes for Efficient and Steady Electrocatalytic H2O2 Generation

Anthraquinone(AQ) modified carbon materials could be endowed with significantly improved oxygen reduction reaction(ORR) activity. However, the application of these materials in the generation of hydrogen peroxide (H2O2) has been rarely investigated. For this motivation, AQ covalently modified carbon nanotube(AQ-CNT) was purposely synthesized for H2O2 generation. It was found that the cumulative H2O2 concentration reached up to 187.18 mg/(Lh) over AQ(40)-CNT catalyst, nearly 2.0 times higher than that over CNT, and being superior to those over most carbon materials reported. The enhanced activity stemmed from the improved mass transfer efficiency of oxygen and the enhanced electrocatalytic activity. Noteworthily, the AQ(40)-CNT material exhibited satisfactory stability for H2O2 generation, which was ascribed to the strong interaction force of C-N covalent bond. The present work could provide a vital idea for designing electrode material with simultaneously improved activity and stability for H2O2 generation.

Zn‐Based Oxides Anchored to Nitrogen‐Doped Carbon Nanotubes as Efficient Bifunctional Catalysts for Zn‐Air Batteries

AbstractZn−Co oxide (ZnCoOx), Zn−Mn oxide (ZnMnOx), Zn−Mn−Co oxide (ZMCO), and Zn−Co−Fe oxide (ZCFO) nanoparticles were successfully synthesized on nitrogen‐doped carbon nanotubes in a one‐pot process. Porous carbon paper was simultaneously impregnated with the catalysts during synthesis and used as air electrodes for Zn‐air batteries. ZnMnOx/N‐CNT catalysts had the best ORR performance in half‐cell LSV experiments with a more positive onset potential than that of Pt−Ru/C (−0.067 V and −0.078 V vs Hg/HgO, respectively). ZCFO/N‐CNT catalysts had the best activity towards OER among the Zn‐based oxide catalysts in half‐cell linear sweep voltammetry (LSV) testing with an onset potential of 0.62 V vs Hg/HgO. Round‐trip efficiencies from battery rate tests at a current density of 20 mA cm−2 were 55.3 %, 57.5 %, 58.7 %, and 58.3 % for ZnCoOx/N‐CNT, ZnMnOx/N‐CNT, ZMCO/N‐CNT, and ZCFO/N‐CNT, respectively. Bifunctional cycling of the catalysts was done in a homemade Zn‐air battery at a current density of 10 mA cm−2 for 200 cycles. The final round trip efficiencies for ZnCoOx/N‐CNT, ZnMnOx/N‐CNT, ZMCO/N‐CNT, and ZCFO/N‐CNT were 55.8 %, 56.6 %, 54.2 %, and 55.0 %, respectively. All catalysts except ZCFO/N‐CNT compared favorably with Pt−Ru/C in terms of round‐trip efficiency after cycling (55.3 %). Incorporation of Zn into the metal oxide particles showed improved catalytic activity for ZnCoOx/N‐CNT and ZnMnOx/N‐CNT compared with MnOx/N‐CNT and CoOx/N‐CNT catalysts prepared via the same technique.

Enhancement of Photocatalytic and Sonophotocatalytic Degradation of 4-nitrophenol by ZnO/Graphene Oxide and ZnO/Carbon Nanotube Nanocomposites

An approach involving ultrasonic irradiation/hydrothermal route was employed for fabricating a series of ZnO nanospheres-carbon nanotubes (Z/CNT) and reduced graphene oxides (Z/GO) nanocomposites, at different weight % ratios of both. The synthesized catalysts were tested in heterogeneous photocatalytic degradation of 4-nitrophenol (4-NP, 10 ppm) via Fenton approach in the attendance of visible light irradiation (160 W, λ > 420), ultrasonic illumination (60 W, 20 kHz) and during coupling the latter irradiations (sonophotocatalysis). The experimental parameters for the Photo-Fenton degradation of 4-NP at the surface of the Z(70)/CNT(30) catalyst were 40 mM H2O2, pH 4, catalyst dosage of 1.75 g/L and at 25 °C. The rate constants of 4-NP degradation using the sonophotocatalytic approach (0.3 min-1); that takes 15 min to accomplish, exceeded those of sonocatalytic (0.15 min-1) and photocatalytic (0.06 min-1) systems, unveiling the synergistic performance of the former system. These values were lower when performing the reaction at the same conditions but at pH 11 to elucidate the importance of the slow releasing of ∙OH in the acid range. The sono- and photo- coupled irradiations induced a synergy percentage comprised of 30 to demonstrate the efficacy of the adopted approach and the catalyst in the degradation of 4-NP.

Novel carbon nanotube supported Co@Ag@Pd formic acid electrooxidation catalysts prepared via sodium borohydride sequential reduction method

At present, monometallic Pd/CNT, bimetallic Pd50Ag50/CNT, Pd50Co50/CNT, Ag50Pd50/CNT catalysts are prepared by NaBH4 co-reduction method. Ag@Pd/CNT catalysts at varying Ag:Pd ratios and Co@Ag@Pd/CNT catalysts at varying Co:Ag:Pd atomic ratios are prepared via NaBH4 sequential reduction method. These catalysts are characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The characterization results show that all catalysts are successfully synthesized at desired molar composition. Furthermore, Ag and Co addition change electronic state of catalyst. Formic acid electrooxidation measurements of these catalysts are performed by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) to investigate the effect of Ag and Co addition through the formic acid electrooxidation activity. Considering the bimetallic catalysts, Ag20@Pd80/CNT exhibits better catalytic activity than the one of other bimetallic catalysts. It is clear that the addition of Ag to Pd improves electrocatalytic activity due to synergetic effects. Furthermore, Co0.072@Ag19.98@Pd79.98/CNT has the best activity, lowest charge transfer resistance (Rct), and a long term stability. EIS and CA results are in a good agreement with CV results. Co0.072@Ag19.98@Pd79.98/CNT is a promising catalyst for Direct formic acid fuel cells.

Efficient nitrogen-doped porous carbon/carbon nanotube-supported Co3O4/Co catalysts for oxygen reduction reactions in alkaline media

In this study, Co3O4/Co nanoparticles are synthesized within nitrogen-doped porous carbon/carbon nanotube matrix (Co3O4/Co@NC/CNT) by using ZIF-67 metal-organic frameworks. In comparison with commercial Pt/C catalysts, the composite exhibits better electrocatalytic characteristics for oxygen reduction reactions in alkaline media, such as onset potential, half-wave potential, current density, cycle stability, and methanol tolerance. For instance, onset potential and half-wave potential are positively shifted by 67 mV and 25 mV, respectively. Structural and composition analysis demonstrate that enhanced properties result from the formation of pyridinic nitrogen and Co-N-C active sites within carbon matrix. The findings above indicate that the Co3O4/Co@NC/CNT catalyst can replace expensive Pt/C catalyst for potential applications in fuel cells and metal-air batteries.

Hydrolysis and electrooxidation of sodium borohydride on novel CNT supported CoBi fuel cell catalyst

At present, Co, Bi, CoBi, and CoBi/CNT catalysts are prepared via co-precipitation method and sodium borohydride (NaBH4) reduction method for NaBH4 electrooxidation and hydrolysis. These Co, Bi, and CoBi catalysts are characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), N2 adsorption-desorption, Inductively Coupled Plasma Mass Spectrometry (ICP-MS), and Temperature Programmed Reduction (TPR). These catalysts are employed for NaBH4 hydrolysis and further measurements are performed to investigate their NaBH4 electrooxidation activity. For NaBH4 hydrolysis, NaOH concentration, reaction temperature, NaBH4 concentration, and catalyst amount are optimized for CoBi and CoBi/CNT catalysts. Furthermore, the rate constants (k) are found between 20 and 50 °C and the activation energy is calculated from the Arrhenius equation. The hydrogen generation rates on CoBi (95–5) and % 10 CoBi (95–5)/CNT catalysts are found as 2605.6 ml H2 g−1cat min−1 and 12996 ml H2 g−1cat min−1, respectively. NaBH4 electrooxidation is investigated with cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) measurements. Maximum mass activities are obtained as 5.86 mA mg−1 Co for CoBi and 25.7 mA mg−1 Co for CoBi/CNT catalysts. EIS and CA results are also in a good agreement with CV results in terms of stability and electrocatalytic activity of CoBi/CNT catalyst. The CoBi/CNT catalyst is believed to be a promising anode catalyst for the direct borohydride fuel cell (DBFC).

Preparation of WO3/CNT catalysts in presence of ionic liquid [C16mim]Cl and catalytic efficiency in oxidative desulfurization

AbstractBACKGROUNDWith the strict regulation for environmental protection, the removal of sulfur compounds from fuels is becoming more and more urgent. Hydrodesulfurization is one of the most widely used technologies in chemical industry, but its application is limited because of the harsh reaction conditions and the low efficiency in removal of aromatic organic sulfide. In this work, catalysts consisting of tungsten trioxide immobilized on carbon nanotubes (WO3/CNT) in the presence of ionic liquid [C16mim]Cl were prepared for the oxidative desulfurization of aromatic organic sulfide.RESULTSThe catalysts were systematically characterized by TG‐DSC, XRD, UV–visible, FTIR, Raman, SEM, TEM, XPS and BET. The dispersion of CNT and the crystal phase of WO3 on the carrier (CNT) were changed in the presence of ionic liquid [C16mim]Cl. The WO3 exists in tetrahedral form when the mass ratio of [C16mim]Cl to CNT is 2. The WO3/CNT catalyst demonstrates better activity in the oxidative desulfurization system, with the removal of dibenzothiophene (DBT) reaching 90.73% under optimal conditions. The oxidation process of DBT follows pseudo‐first‐order kinetics, and the activation energy is about 29.69 kJ mol−1. Dibenzothiophene sulfone (DBTO2) was determined to be the oxidative product of DBT.CONCLUSIONThe results illustrated that the oxidative desulfurization efficiency of different forms of WO3 loaded on the same carrier (CNT) followed the order tetrahedral WO3 &gt; tetragonal phase WO3 &gt; monoclinic phase WO3. © 2019 Society of Chemical Industry

High-performance rechargeable Li-CO2/O2 battery with Ru/N-doped CNT catalyst

The Li-CO2/O2 battery, owing to the sluggish decomposition kinetics of the discharge product Li2CO3, is still far from practical applications. Herein Ru/N-doped carbon nanotube (Ru/NC) catalyst is prepared by solvothermal method and Ru nanoparticles are uniformly distributed on the surface of NC. Due to the superior catalytic activity of Ru nanoparticles and N-doped feature, the decomposition kinetics of the Li2CO3 could be accelerated. Therefore the overpotential of Li-CO2/O2 (VCO2:VO2 = 4:1) battery is decreased from 1.45 V to 1.06 V and thus-assembled battery could operate smoothly for 90 cycles with a capacity of 1000 mAh g−1 or 184 cycles with 500 mAh g−1. XRD and SEM characterizations after cycles further reveal that the as-generated Li2CO3 could be effectively decomposed by the Ru/NC. Besides, with Ru/NC catalyst, Li-CO2/O2 (VCO2:VO2 = 0:1, 2:1 and 1:0) batteries also show enhanced cycling stability of 200, 190 and 150 cycles, respectively, with 500 mAh g−1. Interestingly, the discharge potential increases from 2.35 V to 2.90 V when introducing 20% O2 in Li-CO2 battery. Last but not least, our investigation on the failure mechanism puts an emphasis on the consumption of electrolyte and the degradation of Li anode as the major causes for the decay of the Li-CO2/O2 batteries.