The advancement of modern electronic devices depends strongly on the highly efficient energy sources possessing high energy density and power density. In this regard, supercapacitors show great promise. Due to the unique hierarchical structure, excellent electrical and mechanical properties, and high specific surface area, carbon nanomaterials (particularly, carbon nanotubes, graphene, mesoporous carbon and their hybrids) have been widely investigated as efficient electrode materials in supercapacitors. This review article summarizes progress in high-performance supercapacitors based on carbon nanomaterials with an emphasis on the design and fabrication of electrode structures and elucidation of charge-storage mechanisms. Recent developments on carbon-based flexible and stretchable supercapacitors for various potential applications, including integrated energy sources, self-powered sensors and wearable electronics, are also discussed.

Sustainable and cost-effective energy generation has become crucial for fulfilling present energy requirements. For this purpose, development of cheap, scalable, efficient, and reliable catalysts is essential. Carbon based heteroatom doped, three dimensional and mesoporous electrodes are very promising as catalysts for electrochemical energy conversion and storage. Various carbon allotropes doped with variety of heteroatoms can be utilized for cost-effective mass production of electrode materials. 3D porous carbon electrodes provide multiple advantages, such as, large surface area, maximized exposure to active sites, 3D conductive pathways for efficient electron transport, and porous channels to facilitate electrolyte diffusion. However, it is challenging to synthesize and functionalize isotropic 3D carbon WILEY-VCH This article is protected by copyright. All rights reserved. 2 structures. Here, various synthesis processes of 3D porous carbon materials are summarized to understand how their physical and chemical properties together with heteroatom doping dictate the electrochemical catalytic performance. Prospects of attractive 3D carbon structural materials for energy conversion, and efficient integrated energy systems are also discussed.This article is protected by copyright. All rights reserved. 12Recently, 3D carbon electrodes, including MOF-derived mesoporous carbon structures and carbide derived carbon and onion-like carbon structures, [133] have been prepared by solution based chemical processes, condensation and coordination reactions. Other major printing techniques, such as inkjet printing, screen printing, and transfer printing, have also been commonly used for depositing nanostructured carbons onto substrates of varying size, surface energy, and flexibility for energy applications, though 3D printing is an emerging technology. [134][135][136][137][138][139][140][141][142][143][144] 3D printing can offer porous carbon structures of 10 m thick or thicker with very quick drying time (few sec). [133][134][135][136][137] Carbon allotropic nanomaterials combined with various polymers have been used as highly viscous inks for fabricating 3D printed carbon structures for Li-ion batteries, supercapacitors, water splitting electrolyzers, fuel cells, and environmental protection applications. [136][137][138][139][140] Figure 4 illustrates various electrodes fabricated by different 3D printing methods.

Graphene is a one atom thick carbon allotrope with all surface atoms that has attracted significant attention as a promising material as the conduction channel of a field-effect transistor and chemical field-effect transistor sensors. However, the zero bandgap of semimetal graphene still limits its application for these devices. In this work, ethanol-chemical vapor deposition (CVD) grown p-type semiconducting large-area monolayer graphene film was patterned into nanomesh by the combination of nanosphere lithography and reactive ion etching and evaluated as field-effect transistor and chemiresistor gas sensors. The resulting neck-width of the synthesized nanomesh was about ~20 nm comprised of the gap between polystyrene spheres that was formed during the reactive ion etching process. The neck-width and the periodicities of the graphene nanomesh could be easily controlled depending the duration/power of RIE and the size of PS nanospheres. The fabricated GNM transistor device exhibited promising electronic properties featuring high drive current and ION/IOFF ratio of about 6, significantly higher than its film counterpart. Similarly, when applied as chemiresistor gas sensor at room temperature, the graphene nanomesh sensor showed excellent sensitivity towards NO2 and NH3, significantly higher than their film counterparts. The ethanol-based graphene nanomesh sensors exhibited sensitivities of about 4.32%/ppm in NO2 and 0.71%/ppm in NH3 with limit of detections of 15 ppb and 160 ppb, respectively. Our demonstrated studies on controlling the neck width of the nanomesh would lead to further improvement of graphene-based transistors and sensors.

Precious noble metals (such as, Pt, Ir) and non-precious transition metals (e.g., Fe, Co), including their compounds (e.g., oxides, nitrides), have been widely investigated as efficient catalysts for energy generation, energy conversion, energy storage, important chemical productions, and many industrial processes. However, they often suffer from high cost, low selectivity, poor durability, and susceptibility to gas poisoning with adverse environmental issues. As a low-cost alternative, the first carbon-based metal-free catalyst (i.e., C-MFC based on N-doped carbon nanotubes) was discovered in 2009. Since then, various C-MFCs have been demonstrated to show similar or even better catalytic performance than their metal-based counterparts, attractive for energy conversion and storage (e.g., fuel cells, metalair batteries, water splitting), environmental remediation, and chemical production. Enormous progress has been achieved while the number of publications still rapidly increases every WILEY-VCH This article is protected by copyright. All rights reserved. 2 year. Herein, a critical overview of the very recent advances in this rapidly developing field during the last couple of years is presented.Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff)) Published online: ((will be filled in by the editorial staff))This article is protected by copyright. All rights reserved.62Carbon-based metal-free catalysts (CMFCs), being introduced in 2009, have emerged as low-cost alternative to commercial metal catalysts with similar or even better catalytic performance for energy conversion and storage (e.g., fuel cells, metal-air batteries, water splitting), environmental remediation, and chemical production. A timely critical review of the enormous amount of recent progress in this exciting field is presented.

This article provides a timely and critical review on carbon-based metal-free catalysts for various electrocatalytic reactions, along with the mechanistic and structure–property relationship understanding, current challenges, and future perspectives.