Transition Metal-doped Carbon Research Articles

Progress on Bifunctional Carbon‐Based Electrocatalysts for Rechargeable Zinc–Air Batteries Based on Voltage Difference Performance

AbstractZinc–air batteries (ZABs) hold potential as clean, cost‐effective, and sustainable energy storage system for the next generation. However, the application of ZABs remains challenging because of their poor rechargeability and low efficiency . The design of efficient bifunctional catalysts toward oxygen reduction reaction (ORR) during discharging and the oxygen evolution reaction (OER) during charging is essential to developing rechargeable ZABs. Transition metal (TM)‐doped carbon (TM‐C) materials stand out from all the available bifunctional catalysts due to the excellent specific surface area, diverse morphological structures , and the multiple metal active sites formed after TM doping. This paper, therefore, focuses on the synthesis, electrochemical properties, and potential mechanism of TM‐C catalysts. To make a novelty and logical statement, the voltage difference (ΔE = Ei = 10 − E1/2) between the ORR/OER catalytic process is employed to categorize different TM‐C catalysts reported in recent years, which are divided into two groups: I (ΔE = 0.7 − 0.9 V) and II (ΔE = 0.5 − 0.7 V). The catalytic mechanisms of bifunctional catalysts are clarified. More ways and ideas for synthesizing high‐performance bifunctional TM‐C catalysts are also provided. Finally, the current problem and prospects of this group materials are presented.

Concave Structural Carbon Co-Doped with Iron Atom Pairs and Nitrogen as Ultra-High Performance Catalyst Toward Oxygen Reduction.

It is crucial to rationally design and synthesize atomic-scale transition metal-doped carbon catalysts with high electrocatalytic activity to achieve a high-efficient oxygen reduction reaction (ORR). Herein, an electrocatalyst comprised of Fe-Fe dual atom pairs and N-doped concave carbon are reported (N-CC@Fe DA) that achieves ultrahigh electrocatalytic ORR activity. The catalyst is prepared by a gaseous doping approach, with zeolitic imidazolate framework-8 (ZIF-8) as the carbon framework precursor and cyclopentadienyliron dicarbonyl dimer as the Fe-Fe atom pair precursor. The catalyst exhibits high cathodic ORR catalytic performance in an alkaline Zn/air battery and proton exchange membrane fuel cell (PEMFC), yielding peak power densities of 241 mW cm-2 and 724mWcm-2, respectively, compared to 127 mW cm-2 and 1.20Wcm-2 with conventional Pt/C catalysts as cathodes. The presence of Fe atom pairs coordinate with N atoms is revealed by X-ray photoelectron spectroscopy(XPS) and X-ray absorption spectroscopy (XAS) analysis, and Density Functional Theory (DFT) calculation results show that the Fe-Fe pair structure is beneficial for adsorbing oxygen molecules, activating the O─O bond, and desorbing OH* intermediates formed during oxygen reduction, resulting in a more efficient oxygen reaction. The findings may provide a new pathway for preparing ultra-high-performance doped carbon catalysts with Fe-Fe atom pair structures.

An optical nose based on array of metal-doped carbon dots for identification of hazardous amines and assessing meat freshness

There is an obvious pressing demand for the sensitive and rapid, identification of toxic gases as environmental concerns. In this study, a facile approach for the detection and identification of amine solvents is reported. A colorimetric sensor array composed of different ninhydrin-mediated transition metal-doped carbon dots (TMCDs), deposited on a paper substrate, could sniff the odor of 29 different amines and accomplish their accurate identification. This analytical device generates a unique response pattern for each amine. Modeling the response data of the sensor array by linear discriminate analysis yields a discrimination accuracy of 94 % for the amines. Also, this method allows rapid quantification of ethylamine and isopropylamine in the concentration ranges of 0.008–1600 ppm and 0.05–828 ppm with detection limits of 1.4 ppb and 39 ppb, respectively, which are well below the immediately dangerous to life or health (IDLH) limit concentration for these amines. Interestingly, this sensor array provides discrimination between the isomers of some amines. Moreover, binary and ternary mixtures of amine solvents could be well recognized with this sensor. The application of the sensor array was tested for the assessment of the quality and freshness of some kinds of meat.

Nitrogen and iron co-doped carbon quantum dots/MnO2 nanowire composites for flexible solid-state supercapacitors with high areal capacitance

Herein, the synthesis of MnO2 nanowires decorated with transition metal-doped carbon quantum dots (MCQDs) is described for use as binder-free flexible solid-state supercapacitors. In particular, the water-soluble Fe and N co-doped MCQDs prepared by amidation reaction with ferric ammonium citrate and urea had ultrafine particle morphologies and showed super-hydrophilicity in aqueous solution, which greatly improved the contact probability between the electrode and the electrolyte. In addition, the co-doped MCQDs increased both the electrical conductivity and specific capacitance of the MnO2/carbon-based nanocomposites and limited the collapse and exfoliation of the MnO2 structure during extended cycling. Compared with pristine MnO2 electrode, the MCQDs/MnO2 composite electrode exhibited faster charge-discharge rate and improved cycle stability with increased specific capacitance. The flexible symmetric supercapacitor constructed from the MCQDs/MnO2 composite had a capacitance retention of 85.6 % after 10,000 charge/discharge cycles at a current density of 2 mA cm−2. In addition, the device showed a maximum power density of 4.8 W cm−2 at an energy density of 2.3 mW h cm−2, and a maximum energy density of 11.16 mW h cm−2 at a power density of 311.6 mW cm−2. Data Availability StatementThe data that support the findings of this study are available from the corresponding author upon reasonable request.

(Digital Presentation) Synergistic Effect of Cobalt and Nitrogen on the Spent Coffee Grounds Derived Carbon As an Efficient Catalyst for Alkaline Hydrogen Evolution

Due to global electricity demand and ecological issues, eco-friendly and sustainable energy resource is becoming a hot topic in energy production and future economic development. On this point, efficient catalytic materials for electrochemical hydrogen evolution reaction (HER) are crucial in the research area. HER in alkaline medium has several advantages, including its lower vapor pressure, which helps produce pure hydrogen gas and provides better stability than acidic medium to metal contents by reducing catalyst’s corrosion. Primarily, carbon-based electrocatalytic materials such as hetero-atomic-doped carbon, transition metal-doped carbon, and co-doped carbon show off an effective HER performance. Because it has a large surface area, good chemical stability, it is inexpensive and earth-abundant.Additionally, spent coffee grounds (SCG) contain a high amount of carbohydrates, melanoidins, and lipids that are given a possibility to be suitable carbon precursors for carbon catalyst synthesis. Moreover, SCG is becoming an environmental issue that produces many tons of waste worldwide each year due to the proliferation of global coffee consumption.Here, we present cobalt nanoparticles embedded on nitrogen (N)-doped carbon catalyst, synthesized from SCG. Initially, SCG-derived nanoporous carbon was obtained by pyrolysis under high temperatures with KOH and urea. After that, carbon materials were functionalized with cobalt and nitrogen with the simple method.Cobalt-embedded N-doped carbon catalyst has a high surface area and highly distributed nano-sized pores. Polarization measurement, Tafel plot, electrochemical impedance spectroscopy, chronopotentiometry, and cyclovoltammetry have tested the electrochemical performance. Even though the catalyst contained a negligible amount of cobalt (0.56 at. %), HER catalytic activity in alkaline medium has better resulted than non-functionalized carbon catalysts and was comparable to higher activity benchmark electrocatalysts such as RuO2 and 20% Pt/C. Also, experimental results demonstrate that excellent long-term stability for the alkaline hydrogen evolution. So, synergistic effects of cobalt nanoparticles content and N-doping on the SCG-derived carbon were indicated for efficient catalyst in the alkaline hydrogen evolution application.

Using transition metal-based deep eutectic solvents to synthesize transition metal-doped carbon nitrides for photo-Fenton degradation of organic dyes and antibiotics

Transition metal doped g-C3N4 composites have been proved as promising photo-Fenton catalysts for degrading organic pollutants. The efficient coordination between transition metal ions and nitrogen atoms is crucial to the preparation of transition metal doped g-C3N4 composites. However, it is a challenge to ensure the high coordination efficiency of transition metal ions in g-C3N4. In this work, two series of monometallic doped Cox-g-C3N4 and bimetallic doped Co1.2Fey-g-C3N4 composites were synthesized by employing two transition metal-based deep eutectic solvents (DESs) as reaction media. The mild ionothermal conditions provided a favorable environment for doping transition metal ions in g-C3N4. After annealing these composites, the as-formed Cox-CN and Co1.2Fey-CN composites displayed excellent photo-Fenton activities for degrading organic dyes and antibiotics. Moreover, compared with Cox-CN, Co1.2Fey-CN exhibited enhanced photo-Fenton activities. This research might offer a new approach for preparing transition metal doped g-C3N4 composites in DESs.

Revealing the key role of bonding states in surface chemisorption

It has been widely accepted that the filling of the adsorbate-surface anti-bonding states dominates the variation of adsorption energies among transition metals. However, on the basis of chemical bonding analysis for adsorbate-surface interaction, we find an exception in the adsorption of O, OH, and OOH on nitrogen-coordinated transition metal-doped carbon material. In this material, a weaker (stronger) adsorption is mainly due to the decreasing (increasing) contribution of the filled adsorbate-surface bonding states. This work sheds light on the mechanism of the adsorbate-substrate interaction and suggests that care much be taken in interpreting the surface chemisorption.

Transition metal-doped carbon sphere as enhanced catalysts for oxygen reduction

Herein, carbon sphere (CS-T) were successfully prepared by pyrolyzation melamine formaldehyde resin. And then different transition metals (Fe, Co, Ni) were doped on carbon sphere (CS-M-900). The scanning electron microscopes and elemental mappings prove that the transition metal particles are uniformly doped on the carbon sphere. Meanwhile, the X-ray photoelectron spectrum prove that the transition metals are zero-valence. Furthermore, the electrochemical testings showed the CS-Co-900 had more positive onset potential (0.93 V), half-wave potential (0.84 V), and peak potential (0.81 V). Furthermore, the CS-Co-900 had lower charge transfer resistance (44 Ω) and smaller Tafel slope (65 mV/dec). Most importantly, the oxygen reduction reaction on the CS-Co-900 turned out to be a four electron procedure with excellent methanol tolerance. The improved electrochemical properties towards oxygen reduction reactions of carbon sphere via cobalt doping suggested a design strategy towards future high-performance electrochemical devices.

A DFT study on structural stability and electronic property of VIIIB transition metal-doped carbon nanocaps

Carbon nanocap (CNC) was selected for the systems doped with VIIIB transition metal (TM) atoms. The geometrical structures and electronic properties of TM-doped CNCs were calculated using the density functional theory method. It was found that TM atoms can interact with CNC to form TM–CNC complexes, which corresponded with the large partial charge transfer. All of molecular orbitals of TM–CNC complexes were localized in vicinity doping site. The density of states of these TM-doped CNCs were exhibited mostly metallic or narrow–gap semiconductor.

Density functional theory simulations of complex hydride and carbon-based hydrogen storage materials

This critical review covers the mechanisms underlying density functional theory (DFT) simulations and their relevance in evaluating, developing and discovering new materials. It is intended to be of interest for both experimentalists and theorists in the expanding field of hydrogen storage. We focus on the most studied classes of materials, metal-hydride, -amide, and -borohydride mixtures, and bare and transition metal-doped carbon systems and the utility of DFT simulations for the pre-screening of thermally destabilised reaction paths (170 references).

Synthesis of transition metal-doped carbon xerogels by cogelation

The cogelation process, i.e. the co-polymerization of a metal complex with the gel precursors, was used for the synthesis of transition metal-doped resorcinol–formaldehyde gels. The aim of this process is to anchor the metal to the polymer so that the former does not sinter during the pyrolysis step leading to porous carbon. Cu-, Ni-, Pd- or Pt-loaded gels were prepared by this technique. After drying and pyrolysis, Pd and Pt were obtained as metal nanoparticles (2–5 nm in diameter) inserted in the carbon nodules, when the complexing agent and the synthesis conditions were well chosen. These small metal particles were inaccessible to reactive gases, probably due to carbon deposit at the metal surface during pyrolysis: CO almost did not chemisorb. Oxidation of the support or pyrolysis under reductive atmosphere was applied to the metal-doped gels and carbons in order to make the surface of the metal particles accessible, but these treatments develop the macropores only. The cogelation process is then suitable to prepare metal nanoparticles protected from the outside by encapsulation in the carbon matrix.

Photooxidation of naphthalenesulphonic acids in presence of transition metal-doped carbon aerogels

The aim of the present study was to analyse the activity of carbon aerogels doped with transition metals (Co(II), Mn(II) and Ti(IV)) in the photooxidation process of naphthalenesulphonic acids (1-naphthalenesulphonic (NS), 1,5-naphthalenedisulphonic (NDS) and 1,3,6-naphthalenetrisulphonic (NTS)) from aqueous medium. Results derived from the textural characterization of the aerogels showed that there is no significant influence of the metal added during preparation process (Co(II), Mn(II) or Ti(IV)) on the textural properties of the aerogels. Determination of pH of point of zero charge (pHPZC) and X-ray photoelectron emission spectroscopy (XPS) analyses of the different samples showed them to have highly acidic surfaces (pHPZC≈3–4) with considerably high surface oxygen concentrations (Os≈20%) regardless of the metal present in the aerogel. XPS analysis showed an oxidation state of +2 for Co and Mn, and +4 for Ti. Results obtained demonstrated that photodegradation of naphthalenesulphonic acids with UV radiation (254nm) is not effective. Quantum yield (Φ) values at a wavelength of 254nm were close to zero, showing the low reactivity of these compounds in the photodegradation process. In experiments using a medium-pressure lamp, it was detected that the photodegradation rate of these acids decreased as the number of sulphonic groups present in the aromatic rings increased. Thus, quantum yield values (Φ) for NS, NDS and NTS were 0.019, 0.008 and 0.002, respectively. Presence of Ti(IV) or Co(II) aerogels or of the aerogel prepared without transition metal addition did not affect the photooxidation rate of naphthalenesulphonic acids. However, the addition of Mn(II)-doped carbon aerogel accelerated the elimination rate of these contaminants. These results could indicate that Mn(II)-doped carbon aerogel may act as photocatalyst in NTS photooxidation process. A rise in the surface concentration of Mn increased the NTS photooxidation rate. Activation of Mn aerogel with CO2 markedly increased its microporosity whereas its photocatalytic activity was not enhanced. Presence of tert-butanol (OH radical scavenger) decreased the NTS photodegradation rate, in presence of the Mn aerogel, confirming that oxidation by OH radicals is the main photooxidation pathway. Moreover, the addition of hydrogen peroxide accelerated the NTS photodegradation rate; however, in order to maintain the efficiency of the added hydrogen peroxide, the appropriate dose must be used. Comparison of the results obtained from the photocatalytic activity of the Mn(II) aerogel with TiO2 during photodegradation of naphthalenesulphonic acids showed that TiO2 was more efficient.

Synthesis of transition metal-doped carbon xerogels by solubilization of metal salts in resorcinol–formaldehyde aqueous solution

The pore texture of carbon materials obtained from evaporative drying and pyrolysis of resorcinol–formaldehyde aqueous gels is controlled by the initial pH of the precursors solution. In order to produce transition metal-containing carbons with tailored texture, various metallic salts were dissolved in the precursors solution. When necessary, a complexing agent (HEDTA or DTPA) was added to render the metal ions soluble. Ni, Fe and Pd loaded carbon xerogels were synthesized and their pore texture was studied after evaporative drying and after pyrolysis. The carbon texture was also studied with regard to the nature of the metal and the amount of complexing agent. The solubilization of transition metal salts in the resorcinol–formaldehyde aqueous solution does not prevent the texture regulation, even though this texture control is influenced: the limits of the pH interval leading to micro–mesoporous carbon materials can slightly differ when a metal salt and/or a complexing agent are added. The pH range shift depends mainly on the amount and nature of the complexing agent, but also slightly on the nature of the metal ion. Nevertheless, the metal particles obtained are rather big (diameter > 15 nm). For catalytic applications, the metal dispersion must be enhanced, especially in the case of expensive metals.