Tunable nanoporous carbon
Encyclopedia
Ultracapacitors may have the potential to become key components for energy storage in the industrial market with the rising push for environmental technology
. There are several different approaches to creating ultracapacitors, as detailed here, and tunable nanoporous carbon is a relatively new approach in research dedicated to improving such technology. Researched and developed primarily by Ranjan Dash and Yury Gogotsi of Drexel University
, this approach maximizes the surface area of carbon
for ultracapacitor use. Dash and Gogotsi produce carbon materials known as Carbide
-Derived Carbons (CDCs) from metallic carbides by chemically removing the metallic element, leaving a systematic array of pores on the nanometer level. While ultracapacitors charge quicker than batteries they typically do not hold their charge as long, though materials produced by Dash and Gogotsi have yielded higher energy density, also known as volumetric uptake. According to research published by Dash, Gogotsi and a few other researchers they have been able to increase storage by 75% in some cases through adsorption
treatment with hydrogen in the synthesis
process as well as utilize almost 100% of the surface area exposed by the pores. Ten years of research into the process has provided a technology that may come to be a contender in the renewable energy
market as well as improve fuel storage, toxic gas handling, fuel cells and water desalination
and purification
.
. First CDCs are created by chlorinating the metallic carbides at high temperatures and then H2 is adsorbed into the porous material. According to “Carbide-Derived Carbons: Effect of Pore Size on Hydrogen Uptake”, a paper published by Dash and Gogotsi, “In order to maximize the H2 sorption at the desired temperature and pressure one needs not only to maximize the number of adsorption sites per unit mass and volume of the solid (which could indeed be proportional to SSA) but also tune the H2-solid interaction energy that would allow more sorption sites to adsorb H2 molecules”(where SSA stands for Specific Surface Area). The dissertation states that an increase in the volume of pores with diameter greater than 2 nm causes a decrease in hydrogen adsorption, further demonstrating that a higher volume of small pores correlates with an increase in storage capacity. Experiments were conducted on four CDCs: titanium carbide
(TiC), zirconium carbide
(ZrC), silicon carbide
(SiC), and boron carbide
(B4C). These materials exhibited the best results for fine tuning the pore size distribution (PSD) and are inexpensive, giving much potential to commercialization. Research has also shown that there are several influences to the pore size of CDCs, including “the spatial distribution of carbon atoms in the precursor carbide, the synthesis temperature, the size of the chloride molecules, the presence of catalytic particles, and the effect of optional post-treatments, such as purification or activation
”.
By varying the temperature at which the precursor carbides are chlorinated, the size and distribution of pores across the surface of the resulting carbon material may be systematically controlled. Temperatures up to 600°C, considered low temperatures for chlorination
, tend to produce common and uniform pore sizes on an object and increasing beyond that threshold creates larger size pores and broader distribution. Dash and Gogotsi believe that smaller pores are more efficient in H2 sorption because there is a strong reaction with hydrogen molecules and state that, “The total interaction between the adsorbate molecule and a solid is greater if the molecule can interact with a larger number of surface atoms, as happens in small curved pores (Fig. 4a and b) or narrow slit pores”. This is because the carbide has a larger surface area for hydrogen adsorption. It is possible that there are other factors involved with the carbide structure that may affect or influence sorption properties such as “pore shape, degree of disorder, or internal surface chemistry”. Through research TiC-derived CDC (TiC-CDC) has shown the greatest potential storage capacity after testing TiC-CDCs synthesized at temperatures of 400°C, 600°C, 800°C, and 1000°C and compared to TiC-CDCs treated in hydrogen at temperatures of 400°C and 800°C.
According to a Doctoral dissertation submitted by Dash in 2006, CDCs have been proven to have a greater volumetric and gravimetric storage capacity compared to other carbon-based storage technologies such as single-walled carbon nanotubes (SWCNTs), multi-walled CNTs (MWCNTs), and metal-organic framework
s (MOFs). Because TNPC works with gas for energy storage pressure may affect the capacity of the material. Dash writes, “Considering that only 30% of the total CDC pore volume accessible to Ar
is currently used by H2 at ambient pressure, there is a large potential for increasing capacity at elevated pressure”. The dissertation also states that an increase in the volume of pores with diameter greater than 2 nm causes a decrease in hydrogen adsorption, further demonstrating that a higher volume of small pores correlates with an increase in storage capacity.
Environmental technology
Environmental technology or green technology or clean technology is the application of one or more of environmental science, green chemistry, environmental monitoring and electronic devices to monitor, model and conserve the natural environment and resources, and to curb the negative impacts of...
. There are several different approaches to creating ultracapacitors, as detailed here, and tunable nanoporous carbon is a relatively new approach in research dedicated to improving such technology. Researched and developed primarily by Ranjan Dash and Yury Gogotsi of Drexel University
Drexel University
Drexel University is a private research university with the main campus located in Philadelphia, Pennsylvania, USA. It was founded in 1891 by Anthony J. Drexel, a noted financier and philanthropist. Drexel offers 70 full-time undergraduate programs and accelerated degrees...
, this approach maximizes the surface area of carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
for ultracapacitor use. Dash and Gogotsi produce carbon materials known as Carbide
Carbide
In chemistry, a carbide is a compound composed of carbon and a less electronegative element. Carbides can be generally classified by chemical bonding type as follows: salt-like, covalent compounds, interstitial compounds, and "intermediate" transition metal carbides...
-Derived Carbons (CDCs) from metallic carbides by chemically removing the metallic element, leaving a systematic array of pores on the nanometer level. While ultracapacitors charge quicker than batteries they typically do not hold their charge as long, though materials produced by Dash and Gogotsi have yielded higher energy density, also known as volumetric uptake. According to research published by Dash, Gogotsi and a few other researchers they have been able to increase storage by 75% in some cases through adsorption
Adsorption
Adsorption is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or dissolved solids to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid...
treatment with hydrogen in the synthesis
Chemical synthesis
In chemistry, chemical synthesis is purposeful execution of chemical reactions to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions...
process as well as utilize almost 100% of the surface area exposed by the pores. Ten years of research into the process has provided a technology that may come to be a contender in the renewable energy
Renewable energy
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...
market as well as improve fuel storage, toxic gas handling, fuel cells and water desalination
Desalination
Desalination, desalinization, or desalinisation refers to any of several processes that remove some amount of salt and other minerals from saline water...
and purification
Water purification
Water purification is the process of removing undesirable chemicals, materials, and biological contaminants from contaminated water. The goal is to produce water fit for a specific purpose...
.
Concept
Carbon-based materials have been popular with researchers and developers of ultracapacitors and are useful for the process of physisorptionPhysisorption
Physisorption, also called physical adsorption, is a process in which the electronic structure of the atom or molecule is barely perturbed upon adsorption...
. First CDCs are created by chlorinating the metallic carbides at high temperatures and then H2 is adsorbed into the porous material. According to “Carbide-Derived Carbons: Effect of Pore Size on Hydrogen Uptake”, a paper published by Dash and Gogotsi, “In order to maximize the H2 sorption at the desired temperature and pressure one needs not only to maximize the number of adsorption sites per unit mass and volume of the solid (which could indeed be proportional to SSA) but also tune the H2-solid interaction energy that would allow more sorption sites to adsorb H2 molecules”(where SSA stands for Specific Surface Area). The dissertation states that an increase in the volume of pores with diameter greater than 2 nm causes a decrease in hydrogen adsorption, further demonstrating that a higher volume of small pores correlates with an increase in storage capacity. Experiments were conducted on four CDCs: titanium carbide
Titanium carbide
Titanium carbide, TiC, is an extremely hard refractory ceramic material, similar to tungsten carbide.It is commercially used in tool bits. It has the appearance of black powder with NaCl-type face centered cubic crystal structure...
(TiC), zirconium carbide
Zirconium carbide
Zirconium carbide is an extremely hard refractory ceramic material, commercially used in tool bits for cutting tools. It is usually processed by sintering. It has the appearance of a gray metallic powder with cubic crystal structure...
(ZrC), silicon carbide
Silicon carbide
Silicon carbide , also known as carborundum, is a compound of silicon and carbon with chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive...
(SiC), and boron carbide
Boron carbide
Boron carbide is an extremely hard boron–carbon ceramic material used in tank armor, bulletproof vests, and numerous industrial applications...
(B4C). These materials exhibited the best results for fine tuning the pore size distribution (PSD) and are inexpensive, giving much potential to commercialization. Research has also shown that there are several influences to the pore size of CDCs, including “the spatial distribution of carbon atoms in the precursor carbide, the synthesis temperature, the size of the chloride molecules, the presence of catalytic particles, and the effect of optional post-treatments, such as purification or activation
Activation
Activation in chemical sciences generally refers to the process whereby something is prepared or excited for a subsequent reaction.- Chemistry :...
”.
By varying the temperature at which the precursor carbides are chlorinated, the size and distribution of pores across the surface of the resulting carbon material may be systematically controlled. Temperatures up to 600°C, considered low temperatures for chlorination
Chlorination
Chlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water...
, tend to produce common and uniform pore sizes on an object and increasing beyond that threshold creates larger size pores and broader distribution. Dash and Gogotsi believe that smaller pores are more efficient in H2 sorption because there is a strong reaction with hydrogen molecules and state that, “The total interaction between the adsorbate molecule and a solid is greater if the molecule can interact with a larger number of surface atoms, as happens in small curved pores (Fig. 4a and b) or narrow slit pores”. This is because the carbide has a larger surface area for hydrogen adsorption. It is possible that there are other factors involved with the carbide structure that may affect or influence sorption properties such as “pore shape, degree of disorder, or internal surface chemistry”. Through research TiC-derived CDC (TiC-CDC) has shown the greatest potential storage capacity after testing TiC-CDCs synthesized at temperatures of 400°C, 600°C, 800°C, and 1000°C and compared to TiC-CDCs treated in hydrogen at temperatures of 400°C and 800°C.
According to a Doctoral dissertation submitted by Dash in 2006, CDCs have been proven to have a greater volumetric and gravimetric storage capacity compared to other carbon-based storage technologies such as single-walled carbon nanotubes (SWCNTs), multi-walled CNTs (MWCNTs), and metal-organic framework
Metal-organic framework
Metal-Organic Frameworks are crystalline compounds consisting of metal ions or clusters coordinated to often rigid organic molecules to form one-, two-, or three-dimensional structures that can be porous. In some cases, the pores are stable to elimination of the guest molecules and can be used for...
s (MOFs). Because TNPC works with gas for energy storage pressure may affect the capacity of the material. Dash writes, “Considering that only 30% of the total CDC pore volume accessible to Ar
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
is currently used by H2 at ambient pressure, there is a large potential for increasing capacity at elevated pressure”. The dissertation also states that an increase in the volume of pores with diameter greater than 2 nm causes a decrease in hydrogen adsorption, further demonstrating that a higher volume of small pores correlates with an increase in storage capacity.