A top-down approach for fabricating free-standing bio-carbon supercapacitor electrodes with a hierarchical structure

Hierarchical porous carbon aerogels as a versatile electrode material for high-stability supercapacitors

Supercapacitors (SCs), as new energy storage devices with low cost and high performance, urgently require an electrode material with good pore structure and developed graphitization. Herein, we report a 3D hierarchical porous structured carbon aerogel (CA) obtained via dissolving-gelling and a subsequent carbonizing process. The gelling process was realized by using different types of anti-solvents. The carbon aerogel-acetic acid (CA-AA) has a specific surface area of 616.97 m2 g-1 and a specific capacitance of 138 F g-1 which is superior to cellulose-based active carbon. The CA was assembled into a SC, which showed excellent cycle stability. After charging and discharging 5000 times at the current density of 1 A g-1, the capacitance retention ratio of CA-AA reaches 102%. In addition, CA-AA has an energy density of 10.06 W h kg-1 when the power density is 181.06 W kg-1. It provides a choice for non-activation to effectively regulate the porous structure of biomass carbon materials.

Unleashing the Power of Artificial Intelligence in Materials Design

The integration of artificial intelligence (AI) algorithms in materials design is revolutionizing the field of materials engineering thanks to their power to predict material properties, design de novo materials with enhanced features, and discover new mechanisms beyond intuition. In addition, they can be used to infer complex design principles and identify high-quality candidates more rapidly than trial-and-error experimentation. From this perspective, herein we describe how these tools can enable the acceleration and enrichment of each stage of the discovery cycle of novel materials with optimized properties. We begin by outlining the state-of-the-art AI models in materials design, including machine learning (ML), deep learning, and materials informatics tools. These methodologies enable the extraction of meaningful information from vast amounts of data, enabling researchers to uncover complex correlations and patterns within material properties, structures, and compositions. Next, a comprehensive overview of AI-driven materials design is provided and its potential future prospects are highlighted. By leveraging such AI algorithms, researchers can efficiently search and analyze databases containing a wide range of material properties, enabling the identification of promising candidates for specific applications. This capability has profound implications across various industries, from drug development to energy storage, where materials performance is crucial. Ultimately, AI-based approaches are poised to revolutionize our understanding and design of materials, ushering in a new era of accelerated innovation and advancement.

Bioinspired and Bioderived Aqueous Electrocatalysis

The development of efficient and sustainable electrochemical systems able to provide clean-energy fuels and chemicals is one of the main current challenges of materials science and engineering. Over the last decades, significant advances have been made in the development of robust electrocatalysts for different reactions, with fundamental insights from both computational and experimental work. Some of the most promising systems in the literature are based on expensive and scarce platinum-group metals; however, natural enzymes show the highest per-site catalytic activities, while their active sites are based exclusively on earth-abundant metals. Additionally, natural biomass provides a valuable feedstock for producing advanced carbonaceous materials with porous hierarchical structures. Utilizing resources and design inspiration from nature can help create more sustainable and cost-effective strategies for manufacturing cost-effective, sustainable, and robust electrochemical materials and devices. This review spans from materials to device engineering; we initially discuss the design of carbon-based materials with bioinspired features (such as enzyme active sites), the utilization of biomass resources to construct tailored carbon materials, and their activity in aqueous electrocatalysis for water splitting, oxygen reduction, and CO₂ reduction. We then delve in the applicability of bioinspired features in electrochemical devices, such as the engineering of bioinspired mass transport and electrode interfaces. Finally, we address remaining challenges, such as the stability of bioinspired active sites or the activity of metal-free carbon materials, and discuss new potential research directions that can open the gates to the implementation of bioinspired sustainable materials in electrochemical devices.

Nitrogen and high oxygen-containing metal-free porous carbon nanosheets for supercapacitor and oxygen reduction reaction applications

Herein, the synthesis of heteroatom-containing graphene-like carbon nanosheets (HA-GCNs) by chemical activation of waste biomass, namely peanut shells. As characterized by a variety of analytical and spectroscopy techniques, the as-synthesized HA-GCNs material carbonized at 900 °C was found to possess sheet-like porous nanosheet morphology with high surface areas (>800 m2 g−1) and desirable of heteroatom contents such as nitrogen (N; 0.84 atom%), and oxygen (O) as high as 20.25 atom%, which greatly improved the electronic properties of the carbon substrate for prospective applications as metal-free electrodes and electrocatalytic materials. The HA-GCNs were found to exhibit a superior specific capacitance of 148, 145, 125, and 105 F g−1 corresponding to the KOH, NaOH, LiOH, and H2SO4 electrolyte solutions, respectively. Although, the HA-GCNs electrode exhibited extraordinary electrochemical performances and cyclic charge-discharge stabilities. Moreover, these novel HA-GCNs exhibited excellent electrocatalytic activities and cyclic stabilities for oxygen reduction reaction (ORR) with a desirable current density of 1.17 mA cm−2 in O2-saturated 0.1 M KOH solution, surpassing that of noble metal-incorporated activated carbons. The superior electrochemical and electrocatalytic performances observed for the HA-GCNs were attributed to the unique pseudocapacitive behavior of the oxygen surface functional groups as well as their unique textural properties, rendering practical applications as low-cost electrodes for supercapacitors and metal-free electrocatalysts for ORR.

Blotting Paper-Derived Activated Porous Carbon/Reduced Graphene Oxide Composite Electrodes for Supercapacitor Applications

A facile strategy, engineered for low-cost mass production, to synthesize biomass-derived activated carbon/reduced graphene oxide composite electrodes (GBPCs) by one-pot carbonization of blotting papers containing graphene oxide (GO) and zinc chloride (ZnCl₂) was proposed. Benefitting from the water absorption characteristic of blotting papers in which the voids between the celluloses can easily absorb the GO/ZnCl₂ solution, the chemical activation and reduction of GO can synchronously achieve via one-step carbonization process. As a result, the GBPCs deliver a large specific surface area to accumulate charge. Simultaneously, it provides high conductivity for electron transfer. The symmetric supercapacitor assembled with the optimal GBPCs in 6 M KOH electrolyte exhibits an excellent specific capacitance of 204 F g⁻¹ (0.2 A g⁻¹), outstanding rate capability of 100 F g⁻¹ (20 A g⁻¹). Meanwhile, it still keeps 90% of the initial specific capacitance over 10,000 cycles. The readily available raw material, effective chemical activation, simple rGO additive, and resulting electrochemical properties hold out the promise of hope to achieve low-cost, green, and large-scale production of practical activated carbon composite materials for high-efficiency energy storage applications.

Nile Blue Functionalized Graphene Aerogel as a Pseudocapacitive Negative Electrode Material across the Full pH Range

The pursuit of new negative electrode materials for redox supercapacitors with a high capacitance, boosted energy, and high rate capability is still a tremendous challenge. Herein, we report a Nile Blue conjugated graphene aerogel (NB-GA) as a negative electrode material with excellent pseudocapacitive performance (with specific capacitance of up to 483 F g^-1 at 1 A g^-1) in all acidic, neutral, and alkaline aqueous electrolytes. The contribution from capacitive charge storage represents 93.4% of the total charge, surpassing the best pseudocapacitors known. To assess the feasibility of NB-GA as a negative electrode material across the full pH range, we fabricated three devices, namely, a symmetric NB-GA||NB-GA device in an acidic (1.0 M H₂SO₄) electrolyte, an NB-GA||MnO₂ device in a pH-neutral (1.0 M Na₂SO₄) electrolyte, and an NB-GA||LDH (LDH = Ni-Co-Fe layered double hydroxide) device in an alkaline (1.0 M KOH) electrolyte. The NB-GA||NB-GA device exhibits a maximum specific energy of 22.1 Wh kg^-1 and a specific power of up to 8.1 kW kg^-1; the NB-GA||MnO₂ device displays a maximum specific energy of 55.5 Wh kg^-1 and a specific power of up to 14.9 kW kg^-1, and the NB-GA||LDH device shows a maximum specific energy of 108.5 Wh kg^-1 and a specific power of up to 25.1 kW kg^-1. All the devices maintain excellent stability over 5000 charge-discharge cycles. The outstanding pseudocapacitive performances of the NB-GA nanocomposites render them a highly promising negative electrode material across the entire pH range.

Natural biomass derived hard carbon and activated carbons as electrochemical supercapacitor electrodes

With every moving day, the aspect that is going to be the most important for modern science and technology is the means to supply sufficient energy for all the scientific applications. As the resource of fossil fuel is draining out fast, an alternative is always required to satisfy the needs of the future world. Limited resources also force to innovate something that can utilise the resource more efficiently. This work is based on a simple synthesis route of biomass derived hard carbon and to exploring the possibility of using it as electrochemical supercapacitors. A cheap, eco-friendly and easily synthesized carbon material is utilized as electrode for electrochemical energy-storage. Four different hard carbons were synthesized from KOH activated banana stem (KHC), phosphoric acid treated banana stem derived carbons (PHC), corn-cob derived hard carbon (CHC) and potato starch derived hard carbons (SHC) and tested as supercapacitor electrodes. KOH-activated hard carbon has provided 479.23 F/g specific capacitance as calculated from its cycle voltammograms. A detailed analysis is done to correlate the results obtained with the material property. Overall, this work provides an in depth analysis of the science behind the components of an electrochemical energy-storage system as well as why the different characterization techniques are required to assess the quality and reliability of the material for electrochemical supercapacitor applications.

Highly Dispersible Hexagonal Carbon-MoS2 -Carbon Nanoplates with Hollow Sandwich Structures for Supercapacitors

MoS₂ , a typical layered transition-metal dichalcogenide, is promising as an electrode material in supercapacitors. However, its low electrical conductivity could lead to limited capacitance if applied in electrochemical devices. Herein, a new nanostructure composed of hollow carbon-MoS₂ -carbon was successfully synthesized through an l-cysteine-assisted hydrothermal method by using gibbsite as a template and polydopamine as a carbon precursor. After calcination and etching of the gibbsite template, uniform hollow platelets, which were made of a sandwich-like assembly of partial graphitic carbon and two-dimensional layered MoS₂ flakes, were obtained. The platelets showed excellent dispersibility and stability in water, and good electrical conductivity due to carbon provided by the calcination of polydopamine coatings. The hollow nanoplate morphology of the material provided a high specific surface area of 543 m²  g^-1 , a total pore volume of 0.677 cm³  g^-1 , and fairly small mesopores (≈5.3 nm). The material was applied in a symmetric supercapacitor and exhibited a specific capacitance of 248 F g^-1 (0.12 F cm^-2 ) at a constant current density of 0.1 A g^-1 ; thus suggesting that hollow carbon-MoS₂ -carbon nanoplates are promising candidate materials for supercapacitors.

Preparation and Application of Biochar-Based Catalysts for Biofuel Production

Firstly, this paper reviews two main methods for biochar synthesis, namely conventional pyrolysis and hydrothermal carbonization (HTC). The related processes are described, and the influences of biomass nature and reaction conditions, especially temperature, are discussed. Compared to pyrolysis, HTC has advantages for processing high-moisture biomass and producing spherical biochar particles. Secondly, typical features of biochar in comparison with other carbonaceous materials are summarized. They refer to the presence of inorganics, surface functional groups, and local crystalline structures made up of highly conjugated aromatic sheets. Thirdly, various strategies for biochar modification are illustrated. They include activation, surface functionalization, in situ heteroatom doping, and the formation of composites with other materials. An appropriate modification is necessary for biochar used as a catalyst. Fourthly, the applications of biochar-based catalysts in three important processes of biofuel production are reviewed. Sulfonated biochar shows good catalytic performance for biomass hydrolysis and biodiesel production. Biodiesel production can also be catalyzed by biochar-derived or -supported solid-alkali catalysts. Biochar alone and biochar-supported metals are potential catalysts for tar reduction during or after biomass gasification. Lastly, the merits of biochar-based catalysts are summarized. Biochar-based catalysts have great developmental prospects. Future work needs to focus on the study of mechanism and process design.

Heterogeneous Fenton-like catalysis of Fe-MOF derived magnetic carbon nanocomposites for degradation of 4-nitrophenol

Magnetic Fe–C_x as heterogeneous Fenton-like catalysts were synthesized by the pyrolysis of Fe-MOF, and the catalytic activity of Fe–C_x for removal of 4-NP was significantly affected by pyrolysis temperature.

A facile biomass based approach towards hierarchically porous nitrogen-doped carbon aerogels

Nitrogen-doped carbon aerogels with hierarchically porous architectures (NHCAs) are prepared via the hydrothermal treatment of cantaloupe and the following activation with potassium hydroxide.