A Facile Approach to Prepare Multiple Heteroatom-Doped Carbon Materials from Imine-Linked Porous Organic Polymers

Nitrogen-Doped Porous Carbon Derived from Covalent Triazine Framework for Catalytic Oxidation of Benzyl Alcohol

The catalytic oxidation of alcohols is an important transformation in the chemical industry. Carbon materials with a large surface area and N doping show great promise as metal-free catalysts for the reaction. In this study, a rich N-containing covalent triazine framework polymerized by cyanuric chloride and p-phenylenediamine was used to synthesize N-doped porous carbon with the assistance of a pore-forming agent-NaCl. First, the mass ratio of the polymer/NaCl was optimized to 1:9. Then, the influence of the pyrolysis temperatures (700-1000 °C) on the materials was studied in detail. It was found that the carbon materials were gradually exfoliated by molten salt at high temperatures. XRD and Raman characterizations showed them with a certain graphitization. The optimal doped carbon CNN-1-9-900 achieved the highest surface area of 199.03 m2g-1 with the largest pore volume of 0.29 cm3g-1. Furthermore, it had a high N content of 9.9 at% with the highest relative proportion of pyridinic/graphitic N. Due to the synergistic effect between the surface area and pyridinic/graphitic N, CNN-1-9-900 showed the best performance for benzyl alcohol oxidation with TBHP at moderate conditions, and the process also worked for its derivatives.

Pd "Kills Two Birds with One Stone" for the Synthesis of Catalyst: Dual Active Sites of Pd Triggers the Kinetics of O2 Electrocatalysis

Noble metal-based catalyst, despite their exorbitant cost, are the only successful catalyst for bifunctional oxygen electrocatalysis owing to their capability to drive forward the reaction rate kinetically. Therefore, it is desirable to diminish the noble metal loading without any compromise in the catalyst performance. In this study, the aim to achieve two goals with one action via a single-step route to have ultra-low loading of Pd in the catalyst. The Pd is used as a catalyst for C─C bond formation followed by complexation reactions or vice versa, in conventional Suzuki-Miyaura cross-coupling (SMCC) reaction, which yields a Pd-based porous organic polymer. Interestingly, it is found that dispersed Pd nanocluster (PdNC ) is present together with Pd single atom doped into nanocarbon (Pd-NC) matrix in the catalyst (PdNC /Pd-NC800 ) that obtained after pyrolysis of the porous polymer. The catalyst exhibits remarkable bifunctional activity and durability towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Further, it is studied that the in situ attenuated total reflection infrared (ATR-IR) spectroscopy at different electrochemical potentials during ORR and OER to observe the reaction intermediates. The homemade zinc-air battery with the catalyst displayed great performance, establishing the significance of PdNC /Pd-NC800 as a bifunctional oxygen electrocatalyst.

Elucidating the Role of Atomically Dilute Copper Centers Impregnating a Phosphamide Polymer for the Preferential Hydrogen Evolution Reaction over CO2 Reduction

Organic polymers have attracted considerable interest in designing a multifunctional electrocatalyst. However, the inferior electro-conductivity of such metal-free polymers is often regarded as a shortcoming. Herein, a nitrogen- and phosphorus-rich polymer with phosphamide functionality (PAP) in the repeating unit has been synthesized from diaminopyridine (DAP) and phenylphosphonic dichloride (PPDC) precursors. The presence of phosphamide oxygen and pyridine nitrogen in the repeating unit of PAP leads to the coordination of the CuII ion and the incorporation of 3.29 wt % in the polymer matrix (Cu30@PAP) when copper salt is used to impregnate the polymer. Combined with a spectroscopic, microscopic, and DFT study, the coordination and geometry of copper in the PAP matrix has been established to be a distorted square planar CuII in a N2O2 ligand environment where phosphamide oxygen and pyridine nitrogen of the PAP coordinate to the metal center. The copper incorporation in the PAP modulates its electrocatalytic activity. On the glassy carbon electrode, PAP shows inferior activity toward the hydrogen evolution reaction (HER) in 0.5 M H2SO4 while 3 wt % copper incorporation (Cu30@PAP) significantly improves the HER performance with an overpotential of 114 mV at 10 mA cm-2. The notable electrochemical activity with Cu30@PAP occurs due to the impregnation of Cu(II) in PAP, improved electro-kinetics, and better charge transfer resistance (Rct). When changing the electrolyte from H2SO4 to CO2-saturated bicarbonate solution at nearly neutral pH, PAP shows HER as the dominant pathway along with the partial reduction of CO2 to formate. Moreover, the use of Cu30@PAP as an electrolcatalyst could not alter the predominant HER path, and only 20% Faradaic efficiency for the CO2 reduced products has been achieved. Post-chronoamperometric characterization of the recovered catalyst suggests an unaltered valence state of the copper ion and the intact chemical structure of PAP. DFT studies unraveled that the copper sites of Cu30@PAP promote water adsorption while phosphamide-NH of the PAP can weakly hold the CO2 adduct via a hydrogen bonding interaction. A detailed calculation has pointed out that the tetra-coordinated copper centers present in the PAP frame are the reactive sites and that the formation of the [CuI-H] intermediate is the rate-limiting step for both HER and its competitive side reaction, i.e., CO2 reduction to formate or CO formation. The high proton concentration in the electrolyte of pH < 7 leads to HER as the predominant pathway. This combined experimental and theoretical study has highlighted the crucial role of copper sites in electrocatalysis, emphasizing the plausible reason for electrocatalytic selectivity.

Porous organic polymers in solar cells

Owing to their unique porosity and large surface area, porous organic polymers (POPs) have shown their presence in numerous novel applications. The tunability and functionality of both the pores and backbone of the material enable its suitability in photovoltaic devices. The porosity induced host-guest configurations as well as periodic donor-acceptor structures benefit the charge separation and charge transfer in photophysical processes. The role of POPS in other critical device components, such as hole transporting layers and electrodes, has also been demonstrated. Herein, this review will primarily focus on the recent progress made in applying POPs for solar cell device performance enhancement, covering organic solar cells, perovskite solar cells, and dye-sensitized solar cells. Based on the efforts in recent years in unraveling POP's photophysical process and its relevance with device performances, an in-depth analysis will be provided to address the gradual shift of attention from an entirely POP-based active layer to other device functional components. Combining the insights from device physics, material synthesis, and microfabrication, we aim to unfold the fundamental limitations and challenges of POPs and shed light on future research directions.

Competition among Refined Hollow Structures in Schiff Base Polymer Derived Carbon Microspheres

Synthetic polymer-derived hollow carbon spheres have great utilitarian value in many fields for which the synthesis of proper polymer precursors is a key process. The exploration of new suitable polymer precursors and the construction of refined hollow structures in emerging polymers are both of great significance for synthetic methodology and novel carbon materials. Here, for the first time Schiff base polymer (SBP) colloid spheres with refined hollow structures were synthesized by tandem gradient growth and confined polymerization processes. The Hill equation was employed as a mathematical model to explain the gradient growth of SBP spheres. The size-dependent inner structure of SBP spheres can be adjusted from hollow to multichamber-surrounded hollow, and then to a multichamber structure. SBP-derived carbon spheres having similar surface area and chemical composition but different inner structures provide an effective way to investigate the relationship between inner structure and performance.

Precisely controlled synthesis of Co/N species containing porous carbon for oxygen reduction reaction via anion exchange and CO2 activation

The synthesis strategy of highly dispersed Co/N-doped porous carbon materials using anion exchange resin and ionic liquids.

How to Make a Cocktail of Palladium Catalysts with Cola and Alcohol: Heteroatom Doping vs. Nanoscale Morphology of Carbon Supports

Sparkling drinks such as cola can be considered an affordable and inexpensive starting material consisting of carbohydrates and sulfur- and nitrogen-containing organic substances in phosphoric acid, which makes them an excellent precursor for the production of heteroatom-doped carbon materials. In this study, heteroatom-doped carbon materials were successfully prepared in a quick and simple manner using direct carbonization of regular cola and diet cola. The low content of carbon in diet cola allowed reaching a higher level of phosphorus in the prepared carbon material, as well as obtaining additional doping with nitrogen and sulfur due to the presence of sweeteners and caffeine. Effects of carbon support doping with phosphorus, nitrogen and sulfur, as well as of changes in textural properties by ball milling, on the catalytic activity of palladium catalysts were investigated in the Suzuki–Miyaura and Mizoroki–Heck reactions. Contributions of the heteroatom doping and specific surface area of the carbon supports to the increased activity of supported catalysts were discussed. Additionally, the possibility of these reactions to proceed in 40% potable ethanol was studied. Moreover, transformation of various palladium particles (complexes and nanoparticles) in the reaction medium was detected by mass spectrometry and transmission electron microscopy, which evidenced the formation of a cocktail of catalysts in a commercial 40% ethanol/water solution.

NiCo2O4 nanoparticles inlaid on sulphur and nitrogen doped and co-doped rGO sheets as efficient electrocatalysts for the oxygen evolution and methanol oxidation reactions

The present work depicts the fabrication of NiCo₂O₄ decorated on rGO, and doped and co-doped rGO and its electrocatalytic activity towards the oxygen evolution reaction and methanol oxidation reaction. The NiCo₂O₄ catalyst with S-doped rGO outperformed the other catalysts, indicating that the sulphur atoms attached on rGO possess low oxophilicity and optimum free energy. This results in facile adsorption of the intermediate products formed during the OER and a rapid release of O₂ molecules. The same catalyst requires an overpotential of 1.51 V vs. RHE to attain the benchmark current density value of 10 mA cm^-2 and shows a Tafel slope of 57 mV dec^-1. It also reveals outstanding stability during its operation for 10 h with a minimum loss in potential. On the other hand, NiCo₂O₄/S,N-rGO reveals superior activity with high efficiency and stability in catalyzing methanol oxidation. The catalyst delivered a low onset potential of 0.12 V vs. Hg/HgO and high current density of 203.4 mA cm^-2 after addition of 0.5 M methanol, revealing the outstanding performance of the electrocatalyst.

Kinetics control over the Schiff base formation reaction for fabrication of hierarchical porous carbon materials with tunable morphology for high-performance supercapacitors

Schiff base formation reaction is highly dynamic, and the microstructure of Schiff base polymers is greatly affected by reaction kinetics. Herein, a series of Schiff base cross-linked polymers (SPs) with different morphologies are synthesized through adjusting the species and amount of catalysts. Nitrogen/oxygen co-doped hierarchical porous carbon nanoparticles (HPCNs), with tunable morphology, specific surface area (SSA) and porosity, are obtained after one-step carbonization. The optimal sample (HPCN-3) possesses a coral reef-like microstructure, high SSA up to 1003 m²g^-1, and a hierarchical porous structure, exhibiting a remarkable specific capacitance of 359.5 F g^-1(at 0.5 A g^-1), outstanding rate capability and cycle stability in a 1 M H₂SO₄electrolyte. Additionally, the normalized electric double layer capacitance (EDLC) and faradaic capacitance of HPCN-3 are 0.239 F m^-2and 10.24 F g^-1respectively, certifying its superior electrochemical performance deriving from coral reef-like structure, high external surface area and efficient utilization of heteroatoms. The semi-solid-state symmetrical supercapacitor based on HPCN-3 delivers a capacitance of 55 F g^-1at 0.5 A g^-1, good cycle stability of 86.7% after 5000 GCD cycles at 10 A g^-1, and the energy density ranges from 7.64 to 4.86 Wh kg^-1.

Nitrogen-Doped Carbons Derived from Imidazole-Based Cross-Linked Porous Organic Polymers

Nitrogen-doped and heteroatom multi-doped carbon materials are considered excellent metal-free catalysts, superior catalyst supports for transition metal particles and single metal atoms (single-atom catalysts), as well as efficient sorbents for gas- and liquid-phase substances. Acid-catalyzed sol-gel polycondensation of hydroxybenzenes with heterocyclic aldehydes yields cross-linked thermosetting resins in the form of porous organic polymers (i.e., organic gels). Depending on the utilized hydroxybenzene (e.g., phenol, resorcinol, phloroglucinol, etc.) and heterocyclic aldehyde variety of heteroatom-doped organic polymers can be produced. Upon pyrolysis, highly porous and heteroatom-doped carbons are obtained. Herein, polycondensation of phloroglucinol with imidazole-2-carboxaldehyde (and other, similar heterocyclic aldehydes with two heteroatoms in the aromatic ring) is utilized to obtain porous, N-doped organic and carbon gels with N-content of up to 16.5 and 12 wt.%, respectively. Utilization of a heterocyclic aldehyde with two different heteroatoms yields dually-doped carbon materials. Upon pyrolysis, the porous polymers yield ultramicroporous N-doped and N,S co-doped carbons with specific surface areas of up to 800 m2g-1. The influence of the initial composition of reactants and the pyrolysis temperature on the structure and chemical composition of the final doped organic and carbon materials is studied in detail.

Boron-Doped Nanocrystalline Diamond-Carbon Nanospike Hybrid Electron Emission Source

Electron emission signifies an important mechanism facilitating the enlargement of devices that have modernized large parts of science and technology. Today, the search for innovative electron emission devices for imaging, sensing, electronics, and high-energy physics continues. Integrating two materials with dissimilar electronic properties into a hybrid material is an extremely sought-after synergistic approach, envisioning a superior field electron emission (FEE) material. An innovation is described regarding the fabrication of a nanostructured carbon hybrid, resulting from the one-step growth of boron-doped nanocrystalline diamond (BNCD) and carbon nanospikes (CNSs) by a microwave plasma-enhanced chemical vapor deposition technique. Spectroscopic and microscopic tools are used to investigate the morphological, bonding, and microstructural characteristics related to the growth mechanism of these hybrids. Utilizing the benefits of both the sharp edges of the CNSs and the high stability of BNCD, promising FEE performance with a lower turn-on field of 1.3 V/μm, a higher field enhancement factor of 6780, and a stable FEE current stability lasting for 780 min is obtained. The microplasma devices utilizing these hybrids as a cathode illustrate a superior plasma illumination behavior. Such hybrid carbon nanostructures, with superb electron emission characteristics, can encourage the enlargement of several electron emission device technologies.

Diphenylphosphine-Substituted Ferrocene/Silsesquioxane-Based Hybrid Porous Polymers as Highly Efficient Adsorbents for Water Treatment

The study describes the synthesis of two porous hybrid polymers (abbreviated as DPPF-HPP and DPPOF-HPP) from the Friedel-Crafts reaction of octavinylsilsesquioxane with 1,1'-bis(diphenylphosphine)ferrocene (DPPF) and 1,1'-bis(diphenylphosphine oxide)ferrocene (DPPOF), respectively. DPPF-HPP and DPPOF-HPP possess surface areas of about 890 and 780 m² g^-1, respectively, as well as similar pore structures of the coexisting micropores and mesopores. They are excellent materials for high adsorption of different dyes with adsorption capacities of 2280 mg g^-1 for Congo Red and 1440 mg g^-1 for Crystal Violet. DPPF-HPP also shows a strong affinity to adsorb Hg²⁺ ions (300 mg g^-1). These materials show no sign of degradation under repeated cycles and thus offer potential for wastewater treatment.

MOF derived carbon based nanocomposite materials as efficient electrocatalysts for oxygen reduction and oxygen and hydrogen evolution reactions

The escalating global energy demands and the formidable risks posed by fossil fuels coupled with their rapid depletion have inspired researchers to embark on a quest for sustainable clean energy. Electrochemistry based technologies, e.g., fuel cells, Zn-air batteries or water splitting, are some of the frontrunners of this green energy revolution. The primary concern of such sustainable energy technologies is the efficient conversion and storage of clean energy. Most of these technologies are based on half-cell reactions like oxygen reduction, oxygen and hydrogen evolution reactions, which in turn depend on noble metal based catalysts for their efficient functioning. In order to make such green energy technologies economically viable, the need of the hour is to develop new noble metal free catalysts. Porous carbon, with some assistance from heteroatoms like N or S or earth abundant transition metal or metal oxide nanoparticles, has shown excellent potential in the catalysis of such electrochemical reactions. Metal-organic frameworks (MOFs) containing metal nodes and organic linkers in an ordered morphology with inherent porosity are ideal self-sacrificial templates for such carbon materials. There has been a recent spurt in reports on such MOF-derived carbon based materials as electrocatalysts. In this review, we have presented some of this research work and also discussed the practical reasons behind choosing MOFs for this purpose. Different approaches for synthesizing such carbonaceous materials with unique morphologies and doping, targeted towards superior electrochemical activity, have been documented in this review.