Advanced carbons for gas and energy storage

This thesis describes the synthesis and the characterization of novel porous carbon materials with properties tailored for energy storage or gas sorption applications. The study of carbon-based materials with different texture and porosity properties has focused on improving the performance of electrode materials for electric double-layer capacitors (EDLCs), and also the performance for CO2 and H2 uptakes. The performance of high-power and high-energy EDLCs containing novel activated-carbon electrodes derived from carbon nanotubes (CNTs) with unprecedented high surface areas and specific capacitances is described. The CNTs were synthesised from CCl4 and ferrocene at 180°C, and chemically activated using KOH at a range of temperatures (600 - 900°C). The activated CNTs had surface areas of 1479-2925 m2 g−1 and Brauner-Emmett-Teller (BET) analysis showed that the samples activated at 900°C contained a mix of micropores and small mesopores, while samples activated at lower temperatures were microporous only. In aqueous H2SO4, the highest specific capacitance (172 F g−1) was achieved using a mix of pore sizes and not necessarily the CNTs with the highest surface areas. In EDLCs containing the ionic liquids 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), capacitances of up to 150 F g−1 and wide electrochemical windows (3.0 V) were achieved. The CNT-based EDLCs showed higher specific energies (15 Wh kg−1) and higher power densities (1.5 kW kg−1) than state-of-the-art carbon electrodes for EDLCs and batteries respectively, thus bridging a long-standing performance gap in the Ragone plot describing the relative power and energy densities of these energy storage devices. This thesis is also concerned with CO2 storage, to reduce this greenhouse gas present in the atmosphere with a direct link to global climate change. To this end, a series of novel activated carbons (ACs) from jujun grass and Camellia japonica for CO2 storage were prepared by hydrothermal carbonization of the raw materials, which yielded hydrochars. These were then chemically activated using KOH as the activating agent. The samples were activated at KOH/hydrochar ratios of 2 and 4, and at activating temperatures ranging between 600 °C and 800 °C. The resulting ACs had high surface areas and were predominantly microporous, with moderate to high surface areas (1050 – 3537 m2 g-1). CO2 adsorption by these ACs was investigated in the pressure range 0 - 20 bar at room temperature. The ACs activated at a KOH/hydrochar ratio of 2 were predominantly microporous with surface areas of up to 2,750 m2 g-1. 95% of their surface area was attributed to micropores, while 84% of the pore volume was taken up by micropores, with pore sizes between 5 and 7 Å, and exhibited very promising CO2 uptake capacity of 5.0 mmol g-1 at 1 bar. This is amongst the highest reported so far for biomass-derived carbons. On the other hand, activation at KOH/hydrochar ratio of 4 generates carbons with surface area and pore volume of up to 3,537 m2 g-1 and 1.85 cm3 g-1, respectively, and which, depending on the level of activation, simultaneously exhibit high CO2 uptake at both 1 bar (4.1 mmol g-1) and 20 bar (21.1 mmol g-1), i.e. under conditions that mimic both post combustion and pre combustion CO2 capture from flue gas streams. These observations confirm that CO2 is predominantly adsorbed within the micropores of porous carbons at 1 bar, while the CO2 uptake at 20 bar is proportional to the total surface area. The samples activated at a KOH/carbon ratio of 4, exhibited a H2 uptake capacity up to 6.2 %wt at 20 bar and -196 °C. Considering that the carbon precursors are readily available, cheap and renewable, and that the synthesis of the ACs is simple, the results indicate that these activated carbons are very promising for CO2 and H2 uptake and storage. Nitrogen/sulfur co-doped ACs prepared from polypyrrole and polythiophene as a nitrogen and sulfur precursor, followed by chemical activation using KOH as activating agent were prepared. The ACs have surfaces areas up to 3000 m2 g−1 and the pore size distribution of the ACs depends on the PPY/PTh ratio in the precursor mixture. The ACs are predominantly microporous, but those prepared from 1:2 PPy/PTh mixtures contain a significant proportion of large mesopores (up to 27 Å in diameter). These materials have been tested for their CO2 uptake capabilities, presenting attractive uptake capacities at higher pressures, up to 45 bar. In addition, the materials were tested as electrode materials for supercapacitors in aqueous and ionic liquid electrolytes. In the cell containing an ionic liquid electrolyte, this specific capacitance results in a specific energy, Es, of 107.4 W h kg−1 at a specific power, Ps, of 9.9 kW kg−1, which is unprecedented for ACs in contact with ionic liquids. The study of these nitrogen/sulfur co-doped materials showed promising performance as gas adsorbents and high specific capacitance as electrode materials in EDLCs. Overall, this study showed how to tailor the properties of carbon-based materials for high capacitive performance as electrode materials for supercapacitors as well as for high adsorption behaviour for gas uptake applications. The work revealed in this thesis provides promising results for novel materials for both supercapacitors and gas uptake

Biomass-derived activated carbon with simultaneously enhanced CO2 uptake for both pre and post combustion capture applications

We report on the synthesis and CO2 uptake capabilities of a series of activated carbons derived from biomass raw materials, Jujun grass and Camellia japonica. The carbons were prepared via hydrothermal carbonization of the raw materials, which yielded hydrochars that were activated with KOH at temperature between 600 and 800 °C. Carbons activated at KOH/hydrochar ratio of 2 have moderate to high surface area (1050 – 2750 m2 g-1), are highly microporous (95% of surface area arises from micropores, and 84% of pore volume from micropores of size between 5 and 7 Å), and exhibit excellent CO2 uptake capacity at 25 oC of up to 1.5 mmol g-1 at 0.15 bar and 5.0 mmol g-1 at 1 bar, which is amongst the highest reported so far for biomass-derived carbons. On the other hand, activation at KOH/hydrochar ratio of 4 generates carbons with surface area and pore volume of up to 3,537 m2 g-1 and 1.85 cm3 g-1, and which, depending on level of activation, simultaneously exhibit high CO2 uptake at both 1 bar (4.1 mmol g-1) and 20 bar (21.1 mmol g-1), i.e. under conditions that mimic, respectively, post combustion and pre combustion CO2 capture from flue gas streams. The present carbons are the first examples of biomass derived porous materials with such allround CO2 uptake performance, which arises due to the pore size distribution of the carbons being shifted towards small micropores even for samples with very high surface area. Thus the carbons satisfy the requirements for both low pressure (presence of small micropores) and high pressure (high surface area) CO2 uptake

Bridging the performance gap between electric double-layer capacitors and batteries with high-energy/high-power carbon nanotube-based electrodes

Electric double-layer capacitors (EDLCs) store electrical energy at the interface between charged electrodes and electrolytes and are higher-power devices than batteries. However, the amount of energy stored in EDLCs cannot compete with that in batteries. In this contribution, we describe the development of new EDLCs that can store about as much energy as lead-acid and nickel metal hydride (NiMH) batteries but operate at much higher power densities than achievable using batteries. The electrode materials are derived from carbon nanotubes (CNTs) synthesised from CCl4 and ferrocene at 180 °C, which is drastically lower than the temperatures usually used to synthesise CNTs. By chemically activating the CNTs using KOH, Bruneuer-Emmett-Teller (BET) surface areas reach ~3000 m2/g, which is orders of magnitude higher than those typical of CNTs, and exceeds even that of pristine graphene. Gas sorption analysis shows that the samples activated at 900 °C contain a mix of micropores and small mesopores, while the samples activated at lower temperatures are predominantly microporous. In EDLCs containing aqueous H2SO4 as the electrolyte, the mesoporous carbons exhibit mass-specific capacitances up to 172 F/g, while in the presence of the ionic liquids 1-ethyl-3-methylimidazolium tetrafluoroborate, [EMIM][BF4], and 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4], capacitances up to 150 F/g are measured. Due to the wide potential window of the ionic liquid electrolytes and the unique morphology of the electrode materials, 3-V devices with volume-specific energy densities of the order of 6 Wh/L and mass specific energy densities up to about 15 Wh/kg can be fabricated. The energy stored can be delivered at power densities >1 kW/kg meaning that the performance of these devices bridges the performance gap between those of EDLCs and batteries. The use of this novel electrode material not only allows the fabrication of high- energy/high-power energy storage systems, the methods used to fabricate the electrode materials are inexpensive and can readily be scaled to industrial levels

Advanced carbons for gas and energy storage

This thesis describes the synthesis and the characterization of novel porous carbon materials with properties tailored for energy storage or gas sorption applications. The study of carbon-based materials with different texture and porosity properties has focused on improving the performance of electrode materials for electric double-layer capacitors (EDLCs), and also the performance for CO2 and H2 uptakes. The performance of high-power and high-energy EDLCs containing novel activated-carbon electrodes derived from carbon nanotubes (CNTs) with unprecedented high surface areas and specific capacitances is described. The CNTs were synthesised from CCl4 and ferrocene at 180°C, and chemically activated using KOH at a range of temperatures (600 - 900°C). The activated CNTs had surface areas of 1479-2925 m2 g−1 and Brauner-Emmett-Teller (BET) analysis showed that the samples activated at 900°C contained a mix of micropores and small mesopores, while samples activated at lower temperatures were microporous only. In aqueous H2SO4, the highest specific capacitance (172 F g−1) was achieved using a mix of pore sizes and not necessarily the CNTs with the highest surface areas. In EDLCs containing the ionic liquids 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), capacitances of up to 150 F g−1 and wide electrochemical windows (3.0 V) were achieved. The CNT-based EDLCs showed higher specific energies (15 Wh kg−1) and higher power densities (1.5 kW kg−1) than state-of-the-art carbon electrodes for EDLCs and batteries respectively, thus bridging a long-standing performance gap in the Ragone plot describing the relative power and energy densities of these energy storage devices. This thesis is also concerned with CO2 storage, to reduce this greenhouse gas present in the atmosphere with a direct link to global climate change. To this end, a series of novel activated carbons (ACs) from jujun grass and Camellia japonica for CO2 storage were prepared by hydrothermal carbonization of the raw materials, which yielded hydrochars. These were then chemically activated using KOH as the activating agent. The samples were activated at KOH/hydrochar ratios of 2 and 4, and at activating temperatures ranging between 600 °C and 800 °C. The resulting ACs had high surface areas and were predominantly microporous, with moderate to high surface areas (1050 – 3537 m2 g-1). CO2 adsorption by these ACs was investigated in the pressure range 0 - 20 bar at room temperature. The ACs activated at a KOH/hydrochar ratio of 2 were predominantly microporous with surface areas of up to 2,750 m2 g-1. 95% of their surface area was attributed to micropores, while 84% of the pore volume was taken up by micropores, with pore sizes between 5 and 7 Å, and exhibited very promising CO2 uptake capacity of 5.0 mmol g-1 at 1 bar. This is amongst the highest reported so far for biomass-derived carbons. On the other hand, activation at KOH/hydrochar ratio of 4 generates carbons with surface area and pore volume of up to 3,537 m2 g-1 and 1.85 cm3 g-1, respectively, and which, depending on the level of activation, simultaneously exhibit high CO2 uptake at both 1 bar (4.1 mmol g-1) and 20 bar (21.1 mmol g-1), i.e. under conditions that mimic both post combustion and pre combustion CO2 capture from flue gas streams. These observations confirm that CO2 is predominantly adsorbed within the micropores of porous carbons at 1 bar, while the CO2 uptake at 20 bar is proportional to the total surface area. The samples activated at a KOH/carbon ratio of 4, exhibited a H2 uptake capacity up to 6.2 %wt at 20 bar and -196 °C. Considering that the carbon precursors are readily available, cheap and renewable, and that the synthesis of the ACs is simple, the results indicate that these activated carbons are very promising for CO2 and H2 uptake and storage. Nitrogen/sulfur co-doped ACs prepared from polypyrrole and polythiophene as a nitrogen and sulfur precursor, followed by chemical activation using KOH as activating agent were prepared. The ACs have surfaces areas up to 3000 m2 g−1 and the pore size distribution of the ACs depends on the PPY/PTh ratio in the precursor mixture. The ACs are predominantly microporous, but those prepared from 1:2 PPy/PTh mixtures contain a significant proportion of large mesopores (up to 27 Å in diameter). These materials have been tested for their CO2 uptake capabilities, presenting attractive uptake capacities at higher pressures, up to 45 bar. In addition, the materials were tested as electrode materials for supercapacitors in aqueous and ionic liquid electrolytes. In the cell containing an ionic liquid electrolyte, this specific capacitance results in a specific energy, Es, of 107.4 W h kg−1 at a specific power, Ps, of 9.9 kW kg−1, which is unprecedented for ACs in contact with ionic liquids. The study of these nitrogen/sulfur co-doped materials showed promising performance as gas adsorbents and high specific capacitance as electrode materials in EDLCs. Overall, this study showed how to tailor the properties of carbon-based materials for high capacitive performance as electrode materials for supercapacitors as well as for high adsorption behaviour for gas uptake applications. The work revealed in this thesis provides promising results for novel materials for both supercapacitors and gas uptake

La botiga pedagògica com a projecte interdisciplinari i transversal al CFGM d'elaboració de productes alimentaris

El marc del TFM està centrat en el projecte de la Botiga Pedagògica que s'ha creat en el cicle formatiu de grau mitjà d'elaboració de productes alimentaris. Consisteix en vendre els productes elaborats per part de l'alumnat durant les pràctiques. Un projecte interdisciplinari, complex i agent motivador per a tot el grup d'alumnes. Aquest projecte ha incorporat la transversalitat al cicle, i és un projecte que involucra a tots els membres de l'institut. Es va construir basant-se amb els resultats d'aprenentatge d'un mòdul professional per poder dur a la pràctica tot el coneixement que reben, relacionar els continguts tractats en diferents mòduls, potenciar les capacitats clau que marca el currículum, fomentar el treball i les relacions cooperatives i promoure la xarxa de comunicació de tots els membres de l'Institut. A més a més, la botiga pedagògica permet donar a conèixer el cicle i generar uns ingressos que s'utilitzen per la compra de matèries primeres per a les pràctiques i algun extra com sortides o material necessari. Per tant, s'ha aconseguit que fos un projecte estès tant a l'alumnat, al professorat, com al personal no docent. A través del TFM s'analitzaran els paràmetres del projecte i s'estudiarà per veure com influeix a l'alumnat

A slurry electrode based on reduced graphene oxide and poly(sodium 4-styrenesulfonate) for applications in microbial electrochemical technologies

A reduced graphene oxide slurry electrode was prepared via electrochemical reduction of graphene oxide, using anionic surfactant poly(sodium 4-styrenesulfonate) to stabilise the suspension. The slurry electrode was characterised for its electrochemical and rheological properties and tested for its application in a microbial electrochemical system under both static and fluidised conditions. Thanks to the high ratio of lateral dimension to thickness, reduced graphene oxide allowed electronic percolation at a particles loading of only 2% (wt.), which is significantly lower than typically applied with other graphitic materials such as activated carbon. The slurry displayed shear thinning behaviour, which is advantageous in real scale applications to guaranteeing homogeneity during fluidisation and to prevent sedimentation under static conditions. When tested under fluidised conditions in a microbial electrochemical device seeded with a mixed microbial consortium, the slurry enabled a 4.7x improvement of catalytic current production compared to static conditions. This approach may represent an important step toward increasing competitiveness and applicability of microbial electrochemical technologies