Jiang Deng

Biomass-derived carbon: synthesis and applications in energy storage and conversion

The explosive growth of energy consumption demands highly efficient energy conversion and storage devices, whose innovation greatly depends on the development of advanced electrode materials and catalysts. Among those advanced materials explored, carbon materials have drawn much attention due to their excellent properties, such as high specific surface area and tunable porous structures. Challenges also come from global warming and environmental pollution, which leads to the requirement of sustainable carbon-rich precursors for carbon materials. Hence, the use of biomass for carbon materials features the concepts of green chemistry. This review summarizes the most advanced progress in biomass-derived carbons for use in fuel cells, electrocatalytic water splitting devices, supercapacitors and lithium-ion batteries. Several synthetic strategies for synthesizing biomass-derived carbons, including direct pyrolysis, hydrothermal carbonization, and ionothermal carbonization, have been reviewed, and the corresponding formation mechanisms and prospects are also discussed. This provides fundamental insight and offers important guidelines for the future design of biomass-derived carbons in specific energy applications.

Inspired by bread leavening: one-pot synthesis of hierarchically porous carbon for supercapacitors

Hierarchically porous carbons (HPCs) show great potential in energy storage due to their high surface area as well as short ion transport path derived from the interconnected porous framework. However, most existing protocols highly rely on nanocasting and soft-templating, which usually make the use of specific raw materials and thus their industrial application unfeasible. It still remains a big challenge to build HPCs from crude biomass, which is abundant on the earth, through a simple one-pot approach. Inspired by leavening of bread, we design a strategy to fabricate HPCs with three-dimensional (3D) hierarchical pores consisting of macro, meso, and micropores. The “leavening method” is conducted simply by mixing the biomass with KHCO3 followed by elevated temperature treatment. Besides the well-defined hierarchical structure, the as-prepared HPCs also exhibit notably large specific areas (up to 1893 m2 g−1). It is noteworthy that this “leavening” strategy is widely applicable to most of the biomass derivatives and biomass, including glucose, cellulose, chitin, starch, rice straw, bamboo, etc. When evaluated as supercapacitor electrode materials in two-electrode test systems, the as-prepared HPCs exhibit an excellent electrochemical performance: a specific capacitance of 253 F g−1, with almost no capacitance loss after 10 000 cycles.

Controlled synthesis of sustainable N-doped hollow core-mesoporous shell carbonaceous nanospheres from biomass

Encompassing ecological and economic concerns, the utilization of biomass to produce carbonaceous materials has attracted intensive research and industrial interest. Using nitrogen containing precursors could realize an in situ and homogeneous incorporation of nitrogen into the carbonaceous materials with a controlled process. Herein, N-doped hollow core-disordered mesoporous shell carbonaceous nanospheres (HCDMSs) were synthesized from glucosamine hydrochloride (GAH), an applicable carbohydrate-based derivative. The obtained HCDMSs possessed controlled size (∼450-50 nm) and shell thickness (∼70-10 nm), suitable nitrogen contents (∼6.7-4.4 wt.%), and Brunauer-Emmett-Teller (BET) surface areas up to 770 m2·g−1. These materials show excellent electrocatalytic activity as a metal-free catalyst for the oxygen reduction reaction (ORR) in both alkaline and acidic media. Specifically, the prepared HCDMS-1 exhibits a high diffusion-limited current, and superior durability and better immunity towards methanol crossover and CO poisoning for ORR in alkaline solution than a commercial 20 wt.% Pt/C catalyst.

Asymmetric Flasklike Hollow Carbonaceous Nanoparticles Fabricated by the Synergistic Interaction between Soft Template and Biomass

The soft template method is broadly applied to the fabrication of hollow-structured nanomaterials. However, due to the instability and the typical spherical shape of these soft templates, the resultant particles have a spherical morphology with a wide size distribution. Herein, we developed a sustainable route to fabricate asymmetric flasklike hollow carbonaceous structures with a highly uniform morphology and a narrow size distribution using the soft template method. A dynamic growth mechanism induced by the synergetic interactions between template and biomass is proposed. The precursors (ribose) provide an acidic environment for sodium oleate during the hydrothermal process in which oleic acid nanoemulsions are initially formed and serve as both template and benign solvent for the amphiphilic derivatives of the precursor. Simultaneously, the cosurfactant P123 facilitates the uniform dispersion of the nanoemulsion and is believed to cause the carbonaceous shells to rupture, providing openings through which the intermediates can enter. These subtle interactions facilitate the formation of the flasklike, asymmetric, hollow, carbonaceous nanoparticles. Furthermore, this unique structure contributes to the high surface area (2335 m2 g-1) of the flasklike carbon particles, which enhances the performance of supercapacitors. These findings may open up an exciting field for exploring anisotropic carbonaceous nanomaterials and for understanding the related mechanisms to provide guidance for the design of increasingly complex carbonaceous materials.

3D-interconnected hierarchical porous N-doped carbon supported ruthenium nanoparticles as an efficient catalyst for toluene and quinoline hydrogenation

Ruthenium nanoparticles (2.6 nm) uniformly dispersed on a three-dimensional (3D) interconnected hierarchical porous N-doped carbon (Ru/NHPC) have been successfully developed, serving as a highly active and stable catalyst for the selective hydrogenation of aromatics under mild conditions. A novel “leavening” strategy, i.e. using biomass-derived α-cellulose as a carbon precursor and ammonium oxalate as both a nitrogen source and foaming agent, affords the NHPC material a large surface area (870 m2 g−1), an excellent hierarchical nanostructure which acts as a convenient mass transfer channel and a high ability in stabilizing and dispersing Ru nanoparticles. The Ru/NHPC catalyst exhibits a substantially enhanced activity for the hydrogenation of toluene (TOF up to 39 000 h−1) and quinoline (TOF up to 2858 h−1) in comparison with Ru/HPC (3D-hierarchical porous carbon without nitrogen doping) and Ru/AC (commercial activated carbon) under the same reaction conditions. Further investigations indicate that the 3D interconnected porous structure and N-doping contribute to the improved diffusion and mass transfer, homogeneous dispersion of ruthenium nanoparticles and high percentage of Ru0 (active sites), which results in considerable catalytic performance. This work offers great potential for the application of supported catalysts based on NHPC materials in fine chemical production with high activity.

Hydrothermal synthesis of manganese oxide encapsulated multiporous carbon nanofibers for supercapacitors

Hydrothermal carbonization (HTC) of biomass to produce one-dimensional carbon materials with hierarchical pores is of significant importance. Here, we fabricate composites of MnOx-encapsulated multiporous carbon nanofibers (M-MCNFs) from naturally available carbohydrates through a dopamine-assisted HTC/ templating process. The introduction of dopamine aids in the formation of the morphology of carbon nanofibers (CNFs) by enhancing the interactions between the hard-templates and carbohydrates. The chosen cryptomelane hard-templates, which are superior to traditional hard-templates, are converted into Mn3O4 nanoparticles embedded in multiporous CNFs (MCNFs), eliminating the need for tedious post deposition procedures to introduce redox active sites. Hence, the obtained hybrids with large surface areas, hierarchical pores, and unique structures show great potential in supercapacitors. This economic and sustainable strategy paves a new way for synthesizing MCNFs and metal oxide-encapsulated MCNFs composites from biomass.

Selective aerobic oxidation of alcohols by a mesoporous graphitic carbon nitride/N-hydroxyphthalimide system under visible-light illumination at room temperature

Abstract By combination of photocatalysis and organocatalysis, a metal-free system composed of mesoporous graphitic carbon nitride (mpg-C3N4) and N-hydroxyphthalimide (NHPI) offers an efficient and environmentally friendly method for the oxidation of alcohols at room temperature. As a wide-band gap semiconductor, mpg-C3N4 absorbs visible light and uses the energy to activate NHPI, resulting in high catalytic activity in the subsequent oxidation of alcohols. Interestingly, the main oxidation product of benzyl alcohol can be tuned from benzoic acid to benzaldehyde by increasing the ratio of mpg-C3N4 in the catalyst system. To further understand the reaction route, electron spin resonance and Fourier transform infrared measurements were carried out, confirming that active oxygen and phthalimide N-oxyl radicals formed in the mpg-C3N4/NHPI system. Based on these results, a catalytic mechanism for the mpg-C3N4/NHPI system was proposed. Moreover, this metal-free system also works well for the oxidation of various aromatic alcohols with good selectivity for aldehydes or ketones.

Nitrogen-doped flower-like porous carbon materials directed by in situ hydrolysed MgO: Promising support for Ru nanoparticles in catalytic hydrogenations

The development of novel, simple, and convenient techniques for the fabrication of porous carbon materials with desirable properties, such as tunable pore structures and the presence of nitrogen functionalities, from renewable and abundant biomasses is required. We herein describe an in situ directing method for the preparation of a nitrogen-doped flower-like porous carbon (NFPC) employing arbitrarily shaped MgO from bio-derived glucosamine chloride (GAH). Experimental evidence demonstrated that the structure directing effect of the Mg(OH)2 nanosheets formed in situ from MgO hydrolysis was key to this process, with the original MgO morphology being irrelevant. Furthermore, this method was applicable for a wide variety of biomass-derived carbon precursors. The resulting NFPC exhibited a high nitrogen content of ≤9 wt.%, and was employed as a support to anchor small Ru nanoparticles (average size = 2.7 nm). The resulting Ru/NFPC was highly active in heterogeneous hydrogenations of toluene and benzoic acid, which demonstrated the advantages of nitrogen doping in terms of boosting catalytic performance.

Morphology Dynamics of Single-Layered Ni(OH)2/NiOOH Nanosheets and Subsequent Fe Incorporation Studied by in Situ Electrochemical Atomic Force Microscopy

Nickel (oxy)hydroxide-based (NiOxHy) materials are widely used for energy storage and conversion devices. Understanding dynamic processes at the solid-liquid interface of nickel (oxy)hydroxide is important to improve reaction kinetics and efficiencies. In this study, in situ electrochemical atomic force microscopy (EC-AFM) was used to directly investigate dynamic changes of single-layered Ni(OH)2 nanosheets during electrochemistry measurements. Reconstruction of Ni(OH)2 nanosheets, along with insertion of ions from the electrolyte, results in an increase of the volume by 56% and redox capacity by 300%. We also directly observe Fe cations adsorb and integrate heterogeneously into or onto the nanosheets as a function of applied potential, further increasing apparent volume. Our findings are important for the fundamental understanding of NiOxHy-based supercapacitors and oxygen-evolution catalysts, illustrating the dynamic nature of Ni-based nanostructures under electrochemical conditions.

Organic-acid-assisted synthesis of a 3D lasagna-like Fe-N-doped CNTs-G framework: An efficient and stable electrocatalyst for oxygen reduction reactions

The scalable preparation of multi-functional three-dimensional (3D) carbon nanotubes and graphene (CNTs-G) hybrids via a well-controlled route is urgently required and challenging. Herein, an easily operated, oxalic acid-assisted method was developed for the in situ fabrication of a 3D lasagna-like Fe-N-doped CNTs-G framework (LMFC) from a precursor designed at the molecular level. The well-organized architecture of LMFC was constructed by multi-dimensionally interconnected graphene and CNTs which derived from porous graphene sheets, to form a fundamentally robust and hierarchical porous structure, as well as favorable conductive networks. The impressive oxygen reduction reaction (ORR) performances in both alkaline and acidic conditions helped confirm the significance of this technically favorable morphological structure. This product was also the subject of research for the exploration of decisive effects on the performance of ORR catalysts with reasonable control variables. The present work further advances the construction of novel 3D carbon architectures via practical and economic routes.