The anode oxygen evolution reaction (OER) is known to largely limit the efficiency of electrolyzers owing to its sluggish kinetics. While crystalline metal oxides are promising as OER catalysts, ...their amorphous phases also show high activities. Efforts to produce amorphous metal oxides have progressed slowly, and how an amorphous structure benefits the catalytic performances remains elusive. Now the first scalable synthesis of amorphous NiFeMo oxide (up to 515 g in one batch) is presented with homogeneous elemental distribution via a facile supersaturated co‐precipitation method. In contrast to its crystalline counterpart, amorphous NiFeMo oxide undergoes a faster surface self‐reconstruction process during OER, forming a metal oxy(hydroxide) active layer with rich oxygen vacancies, leading to superior OER activity (280 mV overpotential at 10 mA cm−2 in 0.1 m KOH). This opens up the potential of fast, facile, and scale‐up production of amorphous metal oxides for high‐performance OER catalysts.
Amorphous NiFeMo oxide (up to 515 g one batch) with homogeneous elemental distribution was synthesized through a facile supersaturated co‐precipitation method. The amorphous NiFeMo oxide undergoes rapid surface self‐reconstruction during OER that forms a metal oxy(hydroxide) active layer with oxygen vacancies, enabling efficient OER catalysis.
Exploring low‐cost and high‐performance nonprecious metal catalysts (NPMCs) for oxygen reduction reaction (ORR) in fuel cells and metal–air batteries is crucial for the commercialization of these ...energy conversion and storage devices. Here we report a novel NPMC consisting of Fe3C nanoparticles encapsulated in mesoporous Fe‐N‐doped carbon nanofibers, which is synthesized by a cost‐effective method using carbonaceous nanofibers, pyrrole, and FeCl3 as precursors. The electrocatalyst exhibits outstanding ORR activity (onset potential of −0.02 V and half‐wave potential of −0.140 V) closely comparable to the state‐of‐the‐art Pt/C catalyst in alkaline media, and good ORR activity in acidic media, which is among the highest reported activities of NPMCs.
Nanocomposite electrocatalyst: A high‐performance electrocatalyst for the oxygen reduction reaction (ORR) is based on Fe3C nanoparticles encapsulated in mesoporous Fe‐N‐doped carbon nanofibers. It can be synthesized from low‐cost and abundant precursors and exhibits excellent electrocatalytic performance for the ORR in both alkaline and acidic media.
Carbon aerogels that are typically prepared using sol–gel chemistry have unique three dimensional networks of interconnected nanometer‐sized particles and thus exhibit many fascinating physical ...properties and great application potentials in widespread fields. To boost the practical applications, it is necessary to develop efficient and low‐cost methods to produce high‐performance carbon aerogels on a large‐scale, preferably in a sustainable way. In 2012, two new classes of aerogels consisting of carbon‐nanofiber (CNF) networks were prepared from biomass‐derived precursors by chemosynthesis (i.e. template‐directed hydrothermal carbonization of carbohydrate) and biosynthesis (i.e. use of bacterial cellulose as precursor), respectively. This Review gives a critical overview of this emerging and rapidly developing field, focusing on the synthetic strategies of the carbon‐nanofiber aerogels and their outstanding physical properties. We also discuss the multifunctional application potentials of the two sorts of carbon aerogels and their nanocomposites, and highlight the challenges and future opportunities in this field.
Aero smiths: Carbon aerogels exhibit many fascinating physical properties and great application potentials in widespread fields. This Review covers recent advances in synthetic strategies, physical properties, and multifunctional applications of two emerging carbon‐nanofiber aerogels derived from chemosynthesis and biosynthesis approaches in a comparative perspective.
Superelastic and fatigue‐resistant materials that can work over a wide temperature range are highly desired for diverse applications. A morphology‐retained and scalable carbonization method is ...reported to thermally convert a structural biological material (i.e., bacterial cellulose) into graphitic carbon nanofiber aerogel by engineering the pyrolysis chemistry. The prepared carbon aerogel perfectly inherits the hierarchical structures of bacterial cellulose from macroscopic to microscopic scales, resulting in remarkable thermomechanical properties. In particular, it maintains superelasticity without plastic deformation even after 2 × 106 compressive cycles and exhibits exceptional temperature‐invariant superelasticity and fatigue resistance over a wide temperature range at least from −100 to 500 °C. This aerogel shows unique advantages over polymeric foams, metallic foams, and ceramic foams in terms of thermomechanical stability and fatigue resistance, with the realization of scalable synthesis and the economic advantage of biological materials.
A graphitic carbon nanofiber aerogel (CNFA) is fabricated from structural biological material (i.e., bacterial cellulose) by engineering pyrolysis chemistry, which perfectly inherits the hierarchical structures from macroscopic to microscopic scales. This CNFA maintains superelasticity without plastic deformation after 2 × 106 compressive cycles, and exhibits temperature‐invariant superelasticity and fatigue resistance over a wide temperature range from −100 to 500 °C.
Carbon aerogels with 3D networks of interconnected nanometer‐sized particles exhibit fascinating physical properties and show great application potential. Efficient and sustainable methods are ...required to produce high‐performance carbon aerogels on a large scale to boost their practical applications. An economical and sustainable method is now developed for the synthesis of ultrathin carbon nanofiber (CNF) aerogels from the wood‐based nanofibrillated cellulose (NFC) aerogels via a catalytic pyrolysis process, which guarantees high carbon residual and well maintenance of the nanofibrous morphology during thermal decomposition of the NFC aerogels. The wood‐derived CNF aerogels exhibit excellent electrical conductivity, a large surface area, and potential as a binder‐free electrode material for supercapacitors. The results suggest great promise in developing new families of carbon aerogels based on the controlled pyrolysis of economical and sustainable nanostructured precursors.
Nano‐woodwork: An economical and sustainable method has now been developed for the synthesis of ultrathin carbon nanofiber (CNF) aerogels by engineering the thermal decomposition chemistry of nanofibrillated wood cellulose. This work suggests great promise in developing new families of carbon aerogels based on the controlled pyrolysis of sustainable nanostructured precursors.
Electrocatalytic reduction of oxygen plays a crucial role in many energy storage and conversion devices. Currently, the development of high-performance carbon-based non-precious-metal (NPM) oxygen ...reduction reaction (ORR) catalysts in acidic media still remains a great challenge. Herein, we report a highly active meso/microporous Fe–N-doped carbon nanofiber (Fe–N-CNF) catalyst prepared via a SiO2-protected shell mediated template method. The SiO2-protected shell not only restricts the free migration of iron species but also traps volatile gaseous substances during the pyrolysis process at high temperature, thus leading to a simultaneous optimization of both the surface functionalities and porous structures of the Fe–N-CNF catalysts. Compared to catalysts prepared without a SiO2-protected shell, the Fe–N-CNF catalysts exhibit a much enhanced ORR activity in an acidic medium, along with a superior long-term stability.
Three dimensional (3D) carbon nanomaterials exhibit great application potential in environmental protection, electrochemical energy storage and conversion, catalysis, polymer science, and advanced ...sensors fields. Current methods for preparing 3D carbon nanomaterials, for example, carbonization of organogels, chemical vapor deposition, and self-assembly of nanocarbon building blocks, inevitably involve some drawbacks, such as expensive and toxic precursors, complex equipment and technological requirements, and low production ability. From the viewpoint of practical application, it is highly desirable to develop a simple, cheap, and environmentally friendly way for fabricating 3D carbon nanomaterials in large scale. On the other hand, in order to extend the application scope and improve the performance of 3D carbon nanomaterials, we should explore efficient strategies to prepare diverse functional nanomaterials based on their 3D carbon structure. Recently, many researchers tend to fabricate high-performance 3D carbon-based nanomaterials from biomass, which is low cost, easy to obtain, and nontoxic to humans. Bacterial cellulose (BC), a typical biomass material, has long been used as the raw material of nata-de-coco (an indigenous dessert food of the Philippines). It consists of a polysaccharide with a β-1,4-glycosidic linkage and has a interconnected 3D porous network structure. Interestingly, the network is made up of a random assembly of cellulose nanofibers, which have a high aspect ratio with a diameter of 20–100 nm. As a result, BC has a high specific surface area. Additionally, BC hydrogels can be produced on an industrial scale via a microbial fermentation process at a very low price. Thus, it can be an ideal platform for design of 3D carbon-based functional nanomaterials. Before our work, no systematic work and summary on this topic had been reported. This Account presents the concepts and strategies of our studies on BC in the past few years, that is, converting cheap biomass into high value-added 3D carbon nanomaterials and designing diverse functional materials on 3D carbon structure. We first briefly introduce the history, constituent, and microstructure features of BC and discuss its advantages as a raw material for preparing the CNF aerogels. Then, we summarize the methods and strategies for preparing various 3D carbon-based nanomaterials from BC. In addition, the potential applications of the developed CNF aerogel based functional materials are also highlighted in this Account, including stretchable conductors, oxygen reduction reaction catalysts, supercapacitors, lithium-ion battery, and oil cleanup. Finally, we give some prospects on the future challenges in this emerging research area of designing CNF aerogel based functional nanomaterials from BC.
By virtue of their extraordinarily high surface areas, ordered pore structures, various compositions, and rich functionality, metal–organic frameworks (MOFs) are of great interest in diverse fields ...such as gas separation, sensing, catalysis, energy, environment science, and biomedicine. However, the difficulty in processing MOF crystals and controlling the MOF superstructure is emerging as a critical issue in their application. Herein, it is reported that a robust template, i.e., nanofibrillated cellulose (NFC), can be used for the synthesis of MOF materials with 1D nanofiber morphology. NFC@MOF core–shell nanofibers with a uniform network structure and high aspect ratios can be prepared by use of this template. The small crystal size, flexibility, and good dispersity of the NFC@MOF nanofibers make it convenient for the macroscale assembly and solution processing of MOF materials. A proof‐of‐concept study is demonstrated wherein freestanding MOF nanofiber membranes represent good performance in applications of water treatment and heterogeneous catalysis reaction. This general synthesis and solution‐processing strategy may herald a new era in promoting the industrial application of MOFs.
A robust template, i.e., nanofibrillated cellulose, can be employed for the synthesis of high‐quality metal–organic frameworks (MOF) materials with 1D nanofiber morphology. The good solution dispersibility and membrane formability of MOF nanofibers surpass traditional MOF powder materials, which facilitates their processing and application.
Aerogels, a type of fascinating material with very low density and high surface area, show many unique properties and unlimited applications. To boost their practical applications, it is necessary to ...develop efficient, controllable, and low‐cost methods to produce high‐performance aerogels on a large‐scale, preferably in a sustainable way. Here, a general strategy is reported for controllable fabrication of a family of carbonaceous nanofiber aerogels (CNFAs) by biomass‐derived nanofibers template‐directed hydrothermal carbonization method. Abundant functional groups are exposed on the surface of the prepared carbonaceous nanofibers. Importantly, in contrast to traditional nature biopolymer‐based aerogels, a superior combination of good recoverability and high strength is achieved for the CNFAs by adjusting the synthetic parameters. The successful synthesis of such fascinating materials provides an excellent platform for design and construction of devices for fast water treatment. The synthetic strategy and sustainable concept presented in this work will open a new way to prepare advanced aerogels with unique properties for wide applications.
Biomass‐derived nanofibers, including amyloid nanofibrils, aminated cellulose nanofibers, and deacetylated chitin nanofibers, are used as templates to direct the hydrothermal carbonization of glucose. The obtained carbonaceous nanofiber aerogels with rigid 3D cross‐linked structures provide an excellent platform for design and construction of powerful devices for fast water purification.
Introducing heating function to oil sorbents opens up a new pathway to the fast cleanup of viscous crude oil spills
in situ
. The oil sorption speed increases with the rise of the temperature, thus ...oil sorbents with high heating temperature are desirable. Besides, the oil sorbents also need to be produced environment-friendly. Here we present carbonized melamine-formaldehyde sponges (CMSs) that exhibited superior heating performance and the CMSs could be massively fabricated through a non-polluting pyrolysis process. The conductive CMSs could be heated over 300 °C with a low applied voltage of 6.9 V and keep above 250 °C for 30 min in the air without obvious damage. Such high heating performance enabled heating up the oil spills with a high rate of 2.65 °C·s
−1
and 14% improvement of oil sorption coefficient compared with the state-of-the-art value. We demonstrated that one joule-heated CMS could continuously and selectively collect viscous oil spills (9,010 mPa·s) 690 times its own weight in one hour. The CMSs will be a highly competitive sorbent material for the fast remediation of future crude oil spills.
