Author Archive

Designing next-generation activated carbons for advanced energy storage applications

Activated carbons for energy storage

Activated carbons for energy storage

In this interesting and informative article, M. Sevilla and R. Mokaya review state-of-the-art synthesis methods for the preparation of activated carbons and their application in energy storage systems. Specifically, the authors detail recent developments in the control of properties such as pore size distribution, surface area and structural and chemical characteristics – and how such properties relate to performance in hydrogen storage and supercapacitors.

Activated carbons have a number of desirable features that make them attractive for use in advanced energy-storage systems. As well as being relatively light-weight, low-cost and chemically inert, they also have very large surface areas (> 1000 m2/g) and high micropore volumes in which to interact with other species. This makes activated carbons particularly useful as supercapacitor electrodes and hydrogen storage materials – where performance is strongly related to surface area and pore characteristics.

In this review, recent developments in the fabrication of activated carbons are discussed, focusing particularly on methods which allow the control of features, such as pore size distribution, surface area and physical and chemical characteristics such as texture, morphology and heteroatom-doping. The relationship between these properties and the performance of these materials as supercapacitor electrodes and their use in hydrogen storage is also looked at in detail, providing a guide for the direction of future research in this very active field.

Interested? Read the full article here:

Energy storage applications of activated carbons: supercapacitors and hydrogen storage

Marta Sevilla and Roberts Mokaya

Energy Environ. Sci., 2014, 7, 1250–1280

DOI: 10.1039/C3EE43525C

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Egg-white derived activated carbons display an eggs-tremely high pseudocapacitance in asymmetric supercapacitors

Scientists in Canada have employed a novel template-free approach to prepare so-called Highly Functionalized Activated Carbons (HFACs) derived from common chicken egg-whites. When employed as the anode in an aqueous asymmetric supercapacitor, the materials display a colossal pseudocapacitance of > 550 F g-1, and double the specific energy in comparison to standard activated carbon.

Supercapacitors are energy-storage devices which, unlike batteries, have the phenomenal ability to charge and discharge within a matter of seconds. This makes them useful for high-power applications such as regenerative breaking in electric vehicles, but their low specific energy (energy per unit mass) limits their use in other applications where batteries are preferred.

Conventional supercapacitors typically employ activated carbon (AC) as both the positive and negative electrodes, and are therefore regarded as symmetric. Asymmetric supercapacitors on the other hand often replace the positive electrode with a nanostructured metal oxide – and, in doing so, can show an improved capacitance and energy density.

In their recent paper, David Mitlin and co-workers found that nitrogen-rich Highly Functionalized Activated Carbons (HFACs) – derived from chicken egg-whites – displayed a colossal pseudocapacitance of > 550 F g-1 when employed as an anode in an aqueous asymmetric supercapacitor system, and had double the specific energy in comparison to standard activated carbon.  This performance rivals that of other state-of-the-art carbons, despite the simple template-free approach and abundance and renewable nature of egg-white precursors.

Find out more about their egg-citing work in their full article:

Colossal pseudocapacitance in a high functionality–high surface area carbon anode doubles the energy of an asymmetric supercapacitor
Zhi Li, Zhanwei Xu, Huanlei Wang, Jia Ding, Beniamin Zahiri, Chris M. B. Holt, Xuehai Tanab and David Mitlin
Energy Environ. Sci., 2014, Advance Article
DOI: 10.1039/c3ee43979h

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Multi-shelled hematite microspheres: high-performance anode materials for the Li-ion battery

Researchers from the University of Science and Technology Beijing, China, have developed a novel technique for the fabrication of multi-shelled α-Fe2O3 microspheres. The spheres, when tested as anode materials for Li-ion batteries (LIB), give ultra-high specific capacity values of up to 1702 mAhg-1, which is about 5 times higher than that of graphite (372 mAhg-1) – the currently employed material for LIB anodes.

The performance of the current generation of LIBs is fundamentally limited by the properties of their material components. The charge stored per gram, or specific capacity, of the anode is one such limiting factor; with graphite restricted to a maximum capacity of 372 mAhg-1. Numerous other materials are capable of exceeding this value, however they typically suffer from poor rechargeability (or cycle stability) owing to the fact they expand/contract considerably upon charge/discharge cycling – which causes the electrodes to crumble.

One such material is α-Fe2O3, or hematite, which, as well as being low-cost, abundant and non-toxic, has a high theoretical capacity of 1000 mAhg-1, however it suffers from a destructive volume change of about 90 % upon cycling. A group led by Dan Wang has managed to overcome this problem by preparing α-Fe2O3 as hollow, thin-shelled, concentric microspheres, which are capable of buffering the mechanical stresses upon cycling and therefore prevent crumbling.

In their paper, they reported stable reversible capacities as high as 1702 mAhg-1, which is record-breaking performance for additive-free α-Fe2O3 – and even beats the maximum theoretical capacity of 1000 mAhg-1. What’s more, the materials also display excellent high-current performance; maintaining a high capacity of about 1100 mAhg-1 at a current rate of 1 Ag-1. The authors attributed this excellent performance to the novel concentric shell structure of the hollow microspheres, which is capable of buffering mechanical stresses whilst providing a high surface area for rapid Li-ion transfer kinetics.

So could Dan Wong’s α-Fe2O3 spheres the next big thing for Li-ion batteries? He-matite just be on to something…

Interested? Read the full article here:

α-Fe2O3 multi-shelled hollow microspheres for lithium ion battery anodes with superior capacity and charge retention

Simeng Xu, Colin M. Hessel, Hao Ren, Ranbo Yu, Quan Jin, Mei Yang, Huijun Zhao and Dan Wang
Energy Environ. Sci., 2014, Advance Article
DOI: 10.1039/C3EE43319F

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

High capacity electrochemical supercapacitors derived from human hair

Researchers from China have demonstrated a simple method to fabricate high-capacity electrode materials from an abundant and low-cost precursor: human hair. The materials display impressive capacitance values of up to 340 Fg-1 – beating commercial devices by a significant margin.

Developing high-performance and low-cost energy storage systems is a key goal in renewable energy research; such devices are required for numerous green-technologies such as electric vehicles and smart grids. In comparison to batteries, supercapacitors have, at the expense of energy density, relatively high power densities, short charging times and long cycle lives. A key goal of supercapacitor research has therefore been to enhance the energy density whilst maintaining these merits, and at the same time minimising cost.

In their recent article, researchers from Soochow University, China, have demonstrated a simple method whereby porous carbon materials can be prepared by high-temperature treatment of an abundant and renewable resource – human hair. When employed as supercapacitor electrodes, the materials displayed excellent performance, with energy densities up to 340 Fg-1 and negligible capacity loss even after 20,000 charge-discharge cycles.

The authors attributed the enhanced performance to the high surface area and porosity of the materials, along with the naturally high abundance of nitrogen and sulphur found in human hair, which dope the resulting carbon after heat-treatment. So will this be the future of energy storage, or is it just a hair-brained idea?

Find out for yourself, read the full article here:

Human Hair-Derived Carbon Flakes for Electrochemical Supercapacitors
Wenjing Qian, Fengxia Sun, Yanhui Xu, Lihua Qiu, Changhai Liu, Suidong Wang, and Feng Yan
Energy Environ. Sci. 2013, Accepted Manuscript
DOI: 10.1039/C3EE43111H, Paper

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)