A space-sacrificed pyrolysis strategy for boron-doped carbon spheres with high supercapacitor performance

Targeting the potential application of morphological carbon in electrode materials, a space-sacrificed pyrolysis strategy was applied for the preparation of boron-doped carbon spheres (B-CSs), using commercial triphenyl borate (TPB) as carbon and boron co-source. The unique structure of TPB play an important role in the sacrificed space, and has notable effect on the surface area of B-CSs. The as prepared B-CSs possess a high surface area and boron content with uniform boron atoms distribution and high surface polarity, which contributes to the improvement of pseudo-capacitance. The sizes, specific surface areas, and boron contents of B-CSs can be easily regulated by varying the experimental parameters. The optimal sample has a boron content of 1.38 at%, surface area of 560 m² g^-1 and specific capacitance of 235F g^-1. We can believe that this work would provide a flexible and extensible preparation technique of B-CSs for electrochemical applications.

Optimization Strategies of Preparation of Biomass-Derived Carbon Electrocatalyst for Boosting Oxygen Reduction Reaction: A Minireview

Oxygen reduction reaction (ORR) has attracted considerable attention for clean energy conversion technologies to reduce traditional fossil fuel consumption and greenhouse gas emissions. Although platinum (Pt) metal is currently used as an electrocatalyst to accelerate sluggish ORR kinetics, the scarce resource and high cost still restrict its further scale-up applications. In this regard, biomass-derived carbon electrocatalysts have been widely adopted for ORR electrocatalysis in recent years owing to their tunable physical/chemical properties and cost-effective precursors. In this minireview, recent advances of the optimization strategies in biomass-derived carbon electrocatalysts towards ORR have been summarized, mainly focusing on the optimization of pore structure and active site. Besides, some current challenges and future perspectives of biomass-derived carbon as high-performance electrocatalysts for ORR have been also discussed in detail. Hopefully, this minireview will afford a guideline for better design of biomass-derived carbon electrocatalysts for ORR-related applications.

Carbon-Based Nanocages: A New Platform for Advanced Energy Storage and Conversion

Energy storage and conversion play a crucial role in modern energy systems, and the exploration of advanced electrode materials is vital but challenging. Carbon-based nanocages consisting of sp² carbon shells feature a hollow interior cavity with sub-nanometer microchannels across the shells, high specific surface area with a defective outer surface, and tunable electronic structure, much different from the intensively studied nanocarbons such as carbon nanotubes and graphene. These structural and morphological characteristics make carbon-based nanocages a new platform for advanced energy storage and conversion. Up-to-date synthetic strategies of carbon-based nanocages, the utilization of their unique porous structure and morphology for the construction of composites with foreign active species, and their significant applications to the advanced energy storage and conversion are reviewed. Structure-performance correlations are discussed in depth to highlight the contribution of carbon-based nanocages. The research challenges and trends are also envisaged for deepening and extending the study and application of this multifunctional material.

Bifunctional Catalysts for Reversible Oxygen Evolution Reaction and Oxygen Reduction Reaction

Metal-air batteries (MABs) and reversible fuel cells (RFCs) rely on the bifunctional oxygen catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Finding efficient bifunctional oxygen catalysts is the ultimate goal and it has attracted a great deal of attention. The dilemma is that a good ORR catalyst is not necessarily efficient for OER, and vice versa. Thus, the development of a new type of bifunctional oxygen catalysts should ensure that the catalysts exhibit high activity for both OER and ORR. Composites with multicomponents for active centers supported on highly conductive matrices could be able to meet the challenges and offering new opportunities. In this Review, the evolution of bifunctional catalysts is summarized and discussed aiming to deliver high-performance bifunctional catalysts with low overpotentials.

Metal-Free Synthesis of Boron-Doped Graphene Glass by Hot-Filament Chemical Vapor Deposition for Wave Energy Harvesting

Property modulation of graphene glass by heteroatom doping such as boron (B) and nitrogen (N) is important to extend its practical applications. However, unlike N doping, research studies about the metal-free synthesis of B-doped graphene on glass through the chemical vapor deposition (CVD) method are rarely reported. Herein, we report a hot-filament CVD approach to prepare B-doped graphene glass using diborane (B₂H₆) as the B dopant. The synthesized B-doped graphene was uniform on a large-scale and composed of nanocrystalline graphene grains. By raising the B₂H₆ flow from 0 to 15 sccm, the B content of graphene was facilely modulated from 0 to 5.3 at. %, accompanied with the improvement of both transparency and conductivity. The B-doped graphene prepared on glass at 15 sccm B₂H₆ flow presented the optimal transparent conductive performance superior to those of most reported graphene glass fabricated by other state-of-the-art approaches. Furthermore, for the first time, the performance of graphene glass for wave energy harvesting has been elaborated. It was found that the output power produced by inserting graphene glass into 0.6 M sodium chloride (NaCl) solution could be improved by more than 6 times through B doping. The significant enhancement resulted from the higher waving voltage and smaller resistance of B-doped graphene on glass than the pristine ones. In addition, the waving voltage inversed the polarity after B doping, which was due to the opposite variation of surface potential of pristine and B-doped graphene after NaCl immersion. This work would pave ways for the metal-free preparation and expand the energy-harvesting applications of B-doped graphene materials.

Fabrication of high B-doped ordered mesoporous carbon with 4-hydroxyphenylborate phenolic resin for supercapacitor electrode materials

The high B-doped ordered mesoporous carbon (HPB-OMC) was prepared by using 4-hydroxyphenylboronic acid-modified phenolic resin (HPBPF) as a boron and carbon precursor via the evaporation-induced self-assembly (EISA) approach. The chemical composite, mesoporous structure, and electrochemical properties of the as-prepared HPB-OMC are investigated. The results show that both highly boron-doped and well-ordered mesoporous structure are achieved for HPB-OMCs, owing to the improvement of solubility of the resins in ethanol, and the enhancement of thermal stability of pore channels during carbonization. Moreover, the HPB-OMCs exhibit an ideal electric double-layer capacitor performance. With the increase of the B-doped content, the specific capacitance of the HPB-OMC electrode rises gradually, then drops off a little. The HPB-OMC with a high B content (3.96 wt%) shows a much high specific capacitance of 183 F g⁻¹ at a current density of 1 A g⁻¹, suggesting its promising application in the field of supercapacitors.

The HPB-OMCs, with 3.96 wt% boron-doped and well-ordered structure, show a much high specific capacitance of 183 F g⁻¹ at the current density of 1 A g⁻¹ and ideal electrochemical performances.

Co2B and Co Nanoparticles Immobilized on the N-B-Doped Carbon Derived from Nano-B4C for Efficient Catalysis of Oxygen Evolution, Hydrogen Evolution, and Oxygen Reduction Reactions

A novel hybrid electrocatalyst of Co₂B and Co nanoparticles immobilized on N-B-doped carbon derived from nano-B₄C (Co₂B/Co/N-B-C/B₄C) is in situ synthesized by pyrolysis of nano-B₄C supporting Co(OH)₂ nanoparticles with melamine. The Co₂B and Co nanoparticles are formed and anchored on the generated N and B codoped carbon and undecomposed B₄C. The hybrid exhibits remarkable catalytic performances toward the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR)-a very small potential of 1.53 V at 10 mA cm^-2 for the OER and a high catalytic kinetics and superior durability for the ORR-which are superior to the RuO₂ and Pt/C catalyst, respectively. Most impressively, the hybrid delivers a very small potential gap of 710 mV, which is lower than those of most bifunctional electrocatalysts reported. In addition, the hybrid also shows a satisfying hydrogen evolution reaction performance offering a small overpotential of 220 mV at 10 mA cm^-2 and wonderful stability. The excellent trifunctional catalytic performances issue from synergetic effects of Co₂B, metal Co, Co/N-doped carbon, and B self-doped carbon coexisting in the hybrid with good interaction mutually. This work provides a new-type efficient multifunctional catalyst for regenerative fuel cell and overall water-splitting technologies.

Fluorine-doped graphene with an outstanding electrocatalytic performance for efficient oxygen reduction reaction in alkaline solution

Doping carbon materials have proved to be the front runners to substitute for Pt as oxygen reduction reaction (ORR) catalysts. Fluorine-doped graphene (FG) has rarely been used as ORR catalyst because of the difficulty in preparation. Herein, we report FG sheets prepared by a thermal pyrolysis graphene oxide (GO) process in the presence of zinc fluoride (ZnF₂) as an efficient electrocatalyst for ORR in the alkaline medium. The results show that the pyrolysis temperature seriously affected the doped fluoride amount and morphology of catalyst. It is found that the FG-1100 catalyst possesses a more positive onset potential, higher current density and better four-electron process for ORR than other FG samples. FG-1100 displays an outstanding ORR catalytic activity that is comparable to that of the commercial Pt/C catalyst. Also, its durability and methanol tolerance ability are superior to those of the commercial Pt/C. The excellent ORR catalytic performance is closely related to its higher doped fluorine amount and wrinkle morphology. The FG catalyst can be developed as a low-cost, efficient and durable catalyst as a viable replacement for the Pt/C catalyst, promoting the commercialization of fuel cells.

A Review of Carbon-Composited Materials as Air-Electrode Bifunctional Electrocatalysts for Metal–Air Batteries

Metal–air batteries (MABs), particularly rechargeable MABs, have gained renewed interests as a potential energy storage/conversion solution due to their high specific energy, low cost, and safety. The development of MABs has, however, been considerably hampered by its relatively low rate capability and its lack of efficient and stable air catalysts in which the former stems mainly from the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) and the latter stems from the corrosion/oxidation of carbon materials in the presence of oxygen and high electrode potentials. In this review, various carbon-composited bifunctional electrocatalysts are reviewed to summarize progresses in the enhancement of ORR/OER and durability induced by the synergistic effects between carbon and other component(s). Catalyst mechanisms of the reaction processes and associated performance enhancements as well as technical challenges hindering commercialization are also analyzed. To facilitate further research and development, several research directions for overcoming these challenges are also proposed.

Sodium-Ion Batteries: Improving the Rate Capability of 3D Interconnected Carbon Nanofibers Thin Film by Boron, Nitrogen Dual-Doping

Boron, nitrogen dual-doping 3D hard carbon nanofibers thin film is synthesized using a facile process. The nanofibers exhibit high specific capacity and remarkable high-rate capability due to the synergistic effect of 3D porous structure, large surface area, and enlarged carbon layer spacing, and the B, N codoping-induced defects.

Iron phosphide nanocrystals decorated in situ on heteroatom-doped mesoporous carbon nanosheets used for an efficient oxygen reduction reaction in both alkaline and acidic media

Oxygen reduction catalysts based on heteroatom-doped mesoporous carbon nanosheets loaded with highly crystalline FeP nanoparticles (FeP@FePNCs) were fabricated using a simple, one-step carbonization–phosphization methodology.

Cu,N-codoped Hierarchical Porous Carbons as Electrocatalysts for Oxygen Reduction Reaction

It remains a huge challenge to develop nonprecious electrocatalysts with high activity to substitute commercial Pt catalysts for oxygen reduction reactions (ORR). Here, the Cu,N-codoped hierarchical porous carbon (Cu-N-C) with a high content of pyridinic N was synthesized by carbonizing Cu-containing ZIF-8. Results indicate that Cu-N-C shows excellent ORR electrocatalyst properties. First of all, it nearly follows the four-electron route, and its electron transfer number reaches 3.92 at -0.4 V. Second, both the onset potential and limited current density of Cu-N-C are almost equal to those of a commercial Pt/C catalyst. Third, it exhibits a better half-wave potential (∼16 mV) than a commercial Pt/C catalyst. More importantly, the Cu-N-C displays better stability and methanol tolerance than the Pt/C catalyst. All of these good properties are attributed to hierarchical structure, high pyridinic N content, and the synergism of Cu and N dopants. The metal-N codoping strategy can significantly enhance the activity of electrocatalysts, and it will provide reference for the design of novel N-doped porous carbon ORR catalysts.

Controllable synthesis of nitrogen-doped hollow carbon nanospheres with dopamine as precursor for CO2 capture

Nitrogen-doped hollow carbon nanospheres are synthesized by using dopamine as carbon and nitrogen sources and tetraethyl orthosilicate as structure-assistant agent.

Generation of open-ended, worm-like and graphene-like structures from layered spherical carbon materials

The generation of open ended worm-like, graphene-like carbon nanostructures from polydispersed Au@SiO₂ spheres and SiO₂ spheres.

Sucrose-derived activated carbons: electron transfer properties and application as oxygen reduction electrocatalysts

ORR electrocatalysts derived from sugar: activated carbons derived from sucrose showed electrocatalytic activity for the oxygen reduction reaction.

Easy access to nitrogen-doped mesoporous interlinked carbon/NiO nanosheet for application in lithium-ion batteries and supercapacitors

We report on a novel nitrogen-doped mesoporous interlinked carbon/NiO nanosheet fabricated using Ni-MOF-8 as the precursor. The as-prepared carbon/NiO nanosheet can exhibit high lithium storage capacity and excellent supercapacitive performance.

Nitrogen-doped ordered mesoporous carbon sphere with short channel as an efficient metal-free catalyst for oxygen reduction reaction

N-OMCS has been fabricated by an aqueous self-assembly method. The formation of the mesoporous structure with short channel facilitates the mass transfer in ORR. The N-OMCS-1.5-900 shows excellent catalytic activity and durability in alkaline media.