In Situ Exfoliated, Edge‐Rich, Oxygen‐Functionalized Graphene from Carbon Fibers for Oxygen Electrocatalysis

Lee

Advanced Energy Materials

2017

152

103

In the pursuit of better electrode kinetics and mass transportation for electrochemical energy applications, 3D graphene‐based electrodes have been receiving increasing research interest. Distinguished from other kinds of 3D graphene structures, the well‐developed, vertically aligned graphene nanosheet arrays (VAGNAs) could be grown on a variety of substrates by plasma‐enhanced chemical vapor deposition (PECVD), forming a 3D interconnected structure with intimate contact with substrates and largely exposed edges, and easily accessible open surfaces of the graphene nanosheets. Ascribing to the combined superior inherent properties of graphene and the special structure configuration, e.g., large surface area, excellent electron transfer capability, outstanding mechanical strength, great chemical and thermal stabilities, and enhanced electrochemical activity, VAGNAs have demonstrated promising applications in supercapacitors, batteries, and fuel cell catalysts. This progress report provides a brief review on the nucleation and growth of VAGNAs, their growth mechanism and properties, and highlights the recent important progress in their electrochemical energy conversion and storage applications, in the views of their pros and cons in comparison with other 3D graphene‐based structures. Challenges and perspectives for future advance are discussed in the end.

Section: Synthesis Of Vagnasmentioning

confidence: 99%

Vertically Aligned Graphene Nanosheet Arrays: Synthesis, Properties and Applications in Electrochemical Energy Conversion and Storage

Lee

Advanced Energy Materials

2017

152

103

Advanced Energy Materials

“…[6][7][8][9][10] However, it remains challenging for nitrogen-doped carbon materials to achieve competitive performance to precious metal catalysts due to low nitrogen concentration.Graphitic carbon nitrides (g-C 3 N 4 ) have shown promising performance to replace nitrogen-doped carbon as a highly efficient catalyst, owing to its ultrahigh nitrogen content (theoretically estimated to be ≈60%) and easily tailored structure. [11][12][13][14][15] It is also well-known that the electrocatalytic performance is determined by catalyst structure and accessibility of active sites.…”

mentioning

confidence: 99%

“…[6][7][8][9][10] However, it remains challenging for nitrogen-doped carbon materials to achieve competitive performance to precious metal catalysts due to low nitrogen concentration.…”

mentioning

confidence: 99%

Surface‐Modified Porous Carbon Nitride Composites as Highly Efficient Electrocatalyst for Zn‐Air Batteries

Niu

Marcus

et al. 2017

142

efficient and earth-abundant catalysts have been successfully developed including nitrogen-doped carbon materials that possess promising electrocatalytic performance for ORR and OER. [6][7][8][9][10] However, it remains challenging for nitrogen-doped carbon materials to achieve competitive performance to precious metal catalysts due to low nitrogen concentration.Graphitic carbon nitrides (g-C 3 N 4 ) have shown promising performance to replace nitrogen-doped carbon as a highly efficient catalyst, owing to its ultrahigh nitrogen content (theoretically estimated to be ≈60%) and easily tailored structure. [11][12][13][14][15] It is also well-known that the electrocatalytic performance is determined by catalyst structure and accessibility of active sites. It is of significant importance to maximize the electrochemical surface area to better facilitate the transport of reactants (OH − and O 2 ), and therefore enhance catalytic activity. [16][17][18] For this aim, various methods have been reported in preparation of porous g-C 3 N 4 . Conventionally, rigid templates (SiO 2 , Al 2 O 3 , and ZnO) are used to fabricate porous g-C 3 N 4 , [19,20] which can effectively improve accessibility and catalytic activity of g-C 3 N 4 . However, these rigid template-based synthesis methods are complicated, involving several steps such as template formation, template dispersion, template removal, and catalyst purification. These time-consuming processes increase the fabrication cost and can even damage the g-C 3 N 4 active sites during template removal by the use of strong acidic or basic etching. Addressing these challenges will require facile and strategic developments to synthesize porous g-C 3 N 4 without using templates.Herein, we developed a top-down and template-free strategy for the fabrication of porous g-C 3 N 4 (PCN) by controlled pyrolysis of Co 2+ /melamine networks in O 2 atmosphere. After mixing PCN with graphene oxide (GO) and thermal treating in sulfur atmosphere, CoS x @PCN/rGO catalyst was synthesized. The developed CoS x @PCN/rGO catalyst exhibited outstanding electrocatalytic activity and stability toward both OER and ORR. The CoS x @PCN/rGO also showed long cyclability as an air electrode in a zinc-air battery system, outperforming Pt and other precious metal electrocatalysts. The remarkable electrocatalytic performance of CoS x @PCN/rGO is attributed to the internally accessible nitrogen sites and the facilitated transport of intermediates in the porous structure.A typical synthesis route of PCN is schematically depicted in Figure 1a: First, cobalt(II) nitrate hexahydrate was mixed with Porous carbon nitride (PCN) composites are fabricated using a top-down strategy, followed by additions of graphene and CoS x nanoparticles. This subsequently enhances conductivity and catalytic activity of PCN (abbreviated as CoS x @PCN/rGO) and is achieved by one-step sulfuration of PCN/ graphene oxides (GO) composite materials. As a result, the as-prepared CoS x @PCN/rGO catalysts display excellent activity and stability towa...

Electrochem. Energ. Rev.

“…Inplane topological defects (e.g., pentagons and heptagons, instead of hexagonal rings) usually exist in graphitic carbon skeletons. These defects can also locally induce Gaussian curvatures to alter bond lengths and rehybridize electron orbitals [114], leading to electron redistribution and therefore high ORR activities [115]. In addition, the ORR performance of N-doped graphene can also be greatly enhanced by Stone-Wales defects, which decrease the HOMO-LUMO energy gap of nanoscale graphene domains and change reaction pathways [116,117].…”

Section: Defect-induced Charge Transfermentioning

confidence: 99%

Carbon-Based Metal-Free Electrocatalysis for Energy Conversion, Energy Storage, and Environmental Protection

Xiao

Zou

et al. 2018

166

103

Carbon-based metal-free catalysts possess desirable properties such as high earth abundance, low cost, high electrical conductivity, structural tunability, good selectivity, strong stability in acidic/alkaline conditions, and environmental friendliness. Because of these properties, these catalysts have recently received increasing attention in energy and environmental applications. Subsequently, various carbon-based electrocatalysts have been developed to replace noble metal catalysts for low-cost renewable generation and storage of clean energy and environmental protection through metal-free electrocatalysis. This article provides an up-to-date review of this rapidly developing field by critically assessing recent advances in the mechanistic understanding, structure design, and material/device fabrication of metal-free carbon-based electrocatalysts for clean energy conversion/storage and environmental protection, along with discussions on current challenges and perspectives. Graphical AbstractKeywords Metal-free electrocatalysis · Carbon-based catalysts · Energy conversion and storage · Environmental protection