- Manipulating the optical properties of carbon dots via fine tuning their structural features
As a new class of sustainable carbon material, “carbon dots” is an umbrella term covering many types of materials. Herein, a broad range of techniques was used to develop the understanding of hydrothermally synthesized carbon dots, and it is shown how fine‐tuning the structural features by simple reduction/oxidation reactions can drastically affect their excited‐state properties. Structural and spectroscopic studies found that photoluminescence originates from direct excitation of localized fluorophores involving oxygen functional groups, whereas excitation at graphene‐like features leads to ultrafast phonon‐assisted relaxation and largely quenches the fluorescent quantum yields. This is arguably the first study to identify the dynamics of photoluminescence including Stokes shift and allow the relaxation pathways in these carbon dots to be fully resolved. This comprehensive investigation sheds light on how understanding the excited‐state relaxation processes in different carbon structures is crucial for tuning the optical properties for any potential commercial applications.
- High-power nitrided TiO2 carbon felt as the negative electrode for all-vanadium redox flow batteries
Abstract –We have discovered a very simple method to address the challenge associated with the low volumetric energy density of free-standing carbon nanofiber electrodes for supercapacitors by electrospinning Kraft lignin in the presence of an oxidizing salt (NaNO3) and subsequent carbonization in a reducing atmosphere. The presence of the oxidative salt decreases the diameter of the resulting carbon nanofibers doubling their packing density from 0.51 to 1.03 mg cm−2 and hence doubling the volumetric energy density. At the same time, the oxidative NaNO3 salt eletrospun and carbonized together with lignin dissolved in NaOH acts as a template to increase the microporosity, thus contributing to a good gravimetric energy density. By simply adjusting the process parameters (amount of oxidizing/reducing agent), the gravimetric and volumetric energy density of the resulting lignin free-standing carbon nanofiber electrodes can be carefully tailored to fit specific power to energy demands. The areal capacitance increased from 147 mF cm−2 in the absence of NaNO3 to 350 mF cm−2 with NaNO3 translating into a volumetric energy density increase from 949 μW h cm−3 without NaNO3 to 2245 μW h cm−3 with NaNO3. Meanwhile, the gravimetric capacitance also increased from 151 F g−1 without to 192 F g−1 with NaNO3.
- Edge-Rich MoS2 Grown on Edge-Oriented Three-dimensional Graphene Glass for High-Performance Hydrogen Evolution, Xuanhua Li, Shaohui Guo, Wei Li, Xingang Ren, Jie Su, Qiang Song, Ana Jorge Sobrido, Bingqing Wei
Abstract – The more exposures of the photocatalytically active sites are one of the essential elements to achieve high photocatalytic efficiency. Through the architecture designs, we have proposed an edge-rich MoS2 nanoarray grown on an edge-oriented three-dimensional (3D) graphene (termed as the 3D-graphene/E-MoS2) via chemical vapor deposition. Unlike the two-dimensional (2D) graphene, the highly conductive and transparent 3D graphene film has been grown at oblique angles on glass (i.e., a graphene glass), providing the large exposed surface area for the loading of more photocatalysts. Then, the abundant photocatalytically active sites can be achieved in the subsequently deposited edge-rich MoS2 nanoarrays, which are significantly beneficial for photocatalytic hydrogen production. The theoretical and experimental studies have revealed the new finding in the substantial improvements of both optical and electrical properties based on the geometrically designed 3D-graphene/E-MoS2 structures. Optically, the excellent light absorption (wavelength range: 300–800 nm) is observed, which is attributed to the favorable energy band for the efficient charge transfer between the electronically interconnected graphene and MoS2, and orientation of the MoS2 crystal face array. Electrically, the edge-rich MoS2 grown on the edge-oriented 3D graphene glass can achieve the optimized charge transport along the 2D vector plane from MoS2 layers to graphene. Consequently, the new hybrid nanostructures exhibit excellent performance as an effective photocatalyst for hydrogen generation from photocatalytic water splitting. The measured hydrogen evolution rate (2232.7 μmol/g/h) under white-light illumination is one of the highest among those photocatalysts reported to date.
- One-Step Synthesis, Structure, and Band Gap Properties of SnO2 Nanoparticles Made by a Low Temperature Nonaqueous Sol–Gel Technique, Mohamed Karmaoui, Ana Belen Jorge, Paul F. McMillan, Abil E. Aliev, Robert C. Pullar, João António Labrincha, David Maria Tobaldi
Abstract – Because of its electrically conducting properties combined with excellent thermal stability and transparency throughout the visible spectrum, tin oxide (SnO2) is extremely attractive as a transparent conducting material for applications in low-emission window coatings and solar cells, as well as in lithium-ion batteries and gas sensors. It is also an important catalyst and catalyst support for oxidation reactions. Here, we describe a novel nonaqueous sol–gel synthesis approach to produce tin oxide nanoparticles (NPs) with a low NP size dispersion. The success of this method lies in the nonhydrolytic pathway that involves the reaction between tin chloride and an oxygen donor, 1-hexanol, without the need for a surfactant or subsequent thermal treatment. This one-pot procedure is carried out at relatively low temperatures in the 160–260 °C range, compatible with coating processes on flexible plastic supports. The NP size distribution, shape, and dislocation density were studied by powder X-ray powder diffraction analyzed using the method of whole powder pattern modeling, as well as high-resolution transmission electron microscopy. The SnO2 NPs were determined to have particle sizes between 3.4 and 7.7 nm. The reaction products were characterized using liquid-state 13C and 1H nuclear magnetic resonance (NMR) that confirmed the formation of dihexyl ether and 1-chlorohexane. The NPs were studied by a combination of 13C, 1H, and 119Sn solid-state NMR as well as Fourier transform infrared (FTIR) and Raman spectroscopy. The 13C SSNMR, FTIR, and Raman data showed the presence of organic species derived from the 1-hexanol reactant remaining within the samples. The optical absorption, studied using UV–visible spectroscopy, indicated that the band gap (Eg) shifted systematically to lower energy with decreasing NP sizes. This unusual result could be due to mechanical strains present within the smallest NPs perhaps associated with the organic ligands decorating the NP surface. As the size increased, we observed a correlation with an increased density of screw dislocations present within the NPs that could indicate relaxation of the stress. We suggest that this could provide a useful method for band gap control within SnO2 NPs in the absence of chemical dopants.
- New insights into the electrochemical behaviour of porous carbon electrodes for supercapacitors, Dina Ibrahim Abouelamaiem, María José Mostazo-López, Guanjie He, Drasti Patela, Tobias P. Neville, Ivan P. Parkin, Dolores Lozano-Castelló, Emilia Morallón, Diego Cazorla-Amorós, Ana Belen Jorge, Rongfang Wang, Shan Ji, Maria-Magdalena Titirici, Paul R. Shearing, Daniel J.L. Brett
Abstract – Activated carbons, with different surface chemistry and porous textures, were used to study the mechanism of electrochemical hydrogen and oxygen evolution in supercapacitor devices. Cellulose precursor materials were activated with different potassium hydroxide (KOH) ratios, and the electrochemical behaviour was studied in 6 M KOH electrolyte. In situ Raman spectra were collected to obtain the structural changes of the activated carbons under severe electrochemical oxidation and reduction conditions, and the obtained data were correlated to the cyclic voltammograms obtained at high anodic and cathodic potentials. Carbon-hydrogen bonds were detected for the materials activated at high KOH ratios, which form reversibly under cathodic conditions. The influence of the specific surface area, narrow microporosity and functional groups in the carbon electrodes on their chemical stability and hydrogen capture mechanism in supercapacitor applications has been revealed.
- Correlating electrochemical impedance with hierarchical structure for porous carbon-based supercapacitors using a truncated transmission line model, Dina Ibrahim Abouelamaiem, Guanjie He, Tobias P Neville, Drasti Patel, Shan Ji, Rongfang Wang, Ivan P Parkin, Ana Belen Jorge, Maria-Magdalena Titirici, Paul R Shearing, Daniel JL Brett
Abstract – This work considers the relationship between the morphology of porous carbon materials used for supercapacitors and the electrochemical impedance spectroscopy (EIS) response. EIS is a powerful tool that can be used to study the porous 3-dimensional electrode behavior in different electrochemical systems. Porous carbons prepared by treatment of cellulose with different compositions of potassium hydroxide (KOH) were used as model systems to investigate the form vs. electrochemical function relationship. A simple equivalent circuit that represents the electrochemical impedance behavior over a wide range of frequencies was designed. The associated impedances with the bulk electrolyte, Faradaic electrode processes and different pore size ranges were investigated using a truncated version of the standard transmission line model. The analysis considers the requirements of porous materials as electrodes in supercapacitor applications, reasons for their non-ideal performance and the concept of ‘best capacitance’ behavior in different frequency ranges.
- Integration of supercapacitors into printed circuit boards, Dina Ibrahim Abouelamaiem, Lara Rasha, Guanjie He, Tobias P. Neville, Jason Millichamp, Tom J. Mason, A. Belen Jorge, Ivan P. Parkin, Maria-Magdalena Titirici, Rongfang Wang, Shan Ji, Paul R. Shearing, Daniel J.L. Brett
Abstract – Physically integrated energy storage devices are gaining increasing interest due to the rapid development of flexible, wearable and portable electronics technology. For the first time, supercapacitor components have been integrated into a printed circuit board (PCB) construct. This proof-of-concept study paves the way for integrating supercapacitors into power electronics devices and hybridising with PCB fuel cells. Commercial Norit activated carbon (NAC) was used as the electrode material and was tested in two types of electrolytes, sodium sulfate (Na2SO4) aqueous electrolyte, and Na2SO4-polyvinyl alcohol (Na2SO4-PVA) gel electrolyte. Electrochemical measurements compare the SC-PCBs to standard two-electrode button-cell supercapacitors. A volumetric energy density of 0.56 mW h cm−3 at a power density of 26 mW cm−3 was obtained in the solid-state SC-PCB system, which is over twice the values acquired in the standard cell configuration. This is due to the removal of bulky components in the standard cell, and/or decreased thickness of the overall device, and thus a decrease in the total volume of the SC-PCB configuration. The results show great potential for embedding supercapacitors into PCBs for a broad range of applications. In addition, further advantages can be realised through close physical integration with other PCB-based electrochemical power systems such as fuel cells.
High performance N‐doped carbon electrodes obtained via hydrothermal carbonization of macroalgae for supercapacitor applications, M. Ren, Z. Jia, Z. Tian, D. Lopez, J. Cai, M. M. Titirici, A. Belen Jorge, ChemElectroChem, just accepted.
The conversion of bio‐waste into useful porous carbons constitutes a very attractive approach to contribute to the development of sustainable energy economy, even more as they can be used in energy storage devices. Here we report the synthesis of N‐doped carbons from hydrothermal carbonization of macroalgae, Enteromorpha prolifera (EP), followed by a mild KOH activation step. The obtained N‐doped carbon microspheres exhibited surface areas of up to ~2000 m2/g with N‐loadings varied in the ranges of 1.4~2.9 at%. By modifying activation temperature, we were able to tune surface chemistry and porosity, achieving excellent control of their properties. The specific capacitance reached value of up to 200 F/g at 1 A/g in 6M KOH, for the sample (AHC‐700) obtained at activation temperature of 700 ºC. The as‐assembled symmetric supercapacitor using the sample (AHC‐800) activated at 800 ºC as the electrodes exhibited superior cycling stability with capacitance retention of up to 96% at 10 A/g even after 10,000 cycles, constituting the highest reported so far for biomass‐derived carbon electrodes. These results show the great potential of N‐doped carbons as electrodes for supercapacitors and confirm the excellent electrochemical properties of biomass‐derived carbons in energy storage technologies.
- Carbon Nitride Materials as Efficient Catalyst Supports for Proton Exchange Membrane Water Electrolyzers, AB Jorge, I Dedigama, TS Miller, P Shearing, DJL Brett, PF McMillan, Nanomaterials, 2018, 8,
Carbon nitride materials with graphitic to polymeric structures (gCNH) were investigated as catalyst supports for the proton exchange membrane (PEM) water electrolyzers using IrO₂ nanoparticles as oxygen evolution electrocatalyst. Here, the performance of IrO₂nan o particles formed and deposited in situ onto carbon nitride support for PEM water electrolysis was explored based on previous preliminary studies conducted in related systems. The results revealed that this preparation route catalyzed the decomposition of the carbon nitride to form a material with much lower N content. This resulted in a significantenhancement of the performance of the gCNH-IrO₂ (or N-doped C-IrO₂) electrocatalyst that was likely attributed to higher electrical conductivity of the N-doped carbon support.
- Freestanding Non-Precious Metal Electrocatalysts for Oxygen Evolution and Reduction Reactions, H-F. Wang, R. Chen, J. Feng, M. Qiao, S. Doczcezczo, Q. Zhang, M. M. Titirici, A. Belen Jorge, ChemElectroChem, 2018, DOI: 10.1002/celc.201800292R1.
Carbon and transition metals have emerged as promising candidates for many energy storage and conversion devices. They facilitate charge transfer reactions whilst showing a good stability. These materials, fabricated as freestanding electrodes pose the potential of simplified electrode manufacturing procedures whilst demonstrating excellent electrocatalytic, mechanical, and structural properties, resulting from interconnected (via chemical or van der Waals force bonded) network structures. In such freestanding configuration, the lack of a binder leads to a better conductivity, ease in the manufacturing processing, and allows a lower catalyst mass loading, all of which lead to obvious benefits. This Minireview summarizes different fabrication techniques of freestanding non‐precious‐metal oxygen electrocatalysts along with their performance towards the oxygen evolution reaction (OER) and/or oxygen reduction reaction (ORR). Here, we discuss electrocatalysts produced by using freestanding substrates and those obtained through the self‐assembly of different precursors. The advantages of using freestanding versus non‐freestanding configurations are also pondered. Challenges and perspectives for freestanding electrocatalysts are presented at the end of the Minireview as a guideline for future studies in the field. This work is expected to serve as inspiration for science colleagues to develop further studies into design, processing and testing strategies of freestanding low‐cost oxygen electrocatalysts.
- Determination of specific capacitance of modified candlenut shell based carbon as electrode material for supercapacitor, Zakir, P. Budi, I. Raya, A. Karim, R. Wulandarai, A. Belen Jorge, J. Phys.: Conf. Ser. 2018, 979, 012024 (1-7).
Surface modification of candlenut shell carbon (CSC) using three chemicals: nitric acid (HNO3), hydrogen peroxide (H2O2), and sulfuric acid (H2SO4) has been carried out. Activation of CSC was performed using H3PO4 solution with different ratio between CSC and activator. Carbon surface area was determined by methylene blue adsorption method. Surface characterization was performed using FTIR spectroscopy and Boehm titration method. Specific capacitance of electrode prepared from CSAC (candlenuts shell activated carbon) materials was quantified by Cyclic Voltammetry (CV) measurement. The surface area before and after activation are 105,127 m2/g, 112,488 m2/g, 124,190 m2/g, and 135,167 m2/g, respectively. Surface modification of CSAC showed the improvement in the chemical functionality of CSAC surface. Analyses using FTIR spectroscopy and Boehm titration showed that modifications with HNO3, H2SO4 and H2O2 on the surface of the CSAC increased the number of oxygen functional groups. As a consequence, the specific capacitance of CSAC modified with 65% HNO3 attained the highest value (127 μF/g). There is an incredible increase by a factor of 298% from electrode which was constructed with un-modified CSAC material. This increase correlates to the largest number of oxygen functional groups of CSAC modified with nitric acid (HNO3).
- Synergistic Relationship between the Three-Dimensional Nanostructure and Electrochemical Performance in Biocarbon Supercapacitor Electrode Materials, Dina Ibrahim Abouelamaiem, Guanjie He, Ivan P Parkin, Tobias Neville, A Belen Jorge, Shan Ji, Rongfang Wang, Magdalena Titirici, Dan Shearing, Paul and Brett, Sustainable Energy & Fuels, just accepted, 2018. doi: 10.1039/C7SE00519A.
A novel study presented herein correlates the multidimensional morphology with the electrochemical performance of activated bio-carbon materials, for supercapacitor devices over multiple length scales. The optimization of the potassium hydroxide (KOH) / cellulose ratio for supercapacitor electrode materials is related to morphological characteristics and corresponding electrochemical performance, as described in terms of porosity, specific surface area, specific capacitance and electrochemical impedance. KOH / cellulose samples with ratios 0.5:1 and 1:1 exhibited the best performance, characterized by a hierarchal porous network structure, high surface area and low cell resistance. Compared with the rest of the manufactured samples and commercial activated carbons, Ketjen Black (KB), Norit activated carbon (NAC) and bead-shaped activated carbon (BAC), the former two samples showed better results in three-electrode systems and coin cells, with specific gravimetric capacitances as high as 187 F g-1 at a current density of 1 A g-1. The high performance is attributed to the morphology of the samples that constituted a combination of micro-, meso- and macro-porosity which consequently gave high specific surface area, high porosity, low cell resistance and high specific capacitance. This further corroborates the structure-performance relationship observed in the author’s model KOH/cellulose system, highlighting that the work can be extended to other similar systems. It is clear that the three-dimensional nanostructure of a material must be understood in its entirety in order to optimize the electrochemical performance.
- Biomass-derived electrodes for flexible supercapacitors. Servann Herou, Philipp Schlee, Ana Belen Jorge, Magdalena Titirici, Current Opinions in Green and Sustainable Chemistry, 2017, 9, 18-24.
- The Importance of Using Alkaline Ionomer Binders for Screening Electrocatalysts in Alkaline Electrolyte, Rhodri Jervis, Noramalina Mansor, A. Belen Jorge, Simon Jones, Christopher Gibbs, Tobias P. Neville, Jason Millichamp, Paul R. Shearing, Daniel J. L. Brett, Journal Electrochemical Society, 2017, 164, F1551-F1555.
Many electrochemical studies exist using the acidic ionomer Nafion as a binder in the ink formulation when operating in high pH systems. However, Nafion acts as an ionic insulator for OH−, and for reactions such as the hydrogen oxidation reaction, the transport of OH− to the catalyst surface is of utmost importance when elucidating the performance of a catalyst. This work demonstrates that when using an alkaline polymer binder in the ink, the apparent activity of a commercially synthesized Pt/C catalyst is increased due to a lower diffusion resistance for the reaction. In order to obtain accurate values for kinetic data in alkaline media, the use of the acidic binder should be avoided.
- Carbon nitrides: synthesis and characterization of a new class of functional materials, Thomas Miller, Ana Belen Jorge, Theo Suter, Andrea Sella, Furio Cora, Paul McMillan, Phys. Chem.Chem.Phys., 2017, 19, 15613–15638.
AbstractCarbon nitride compounds with high N : C ratios and graphitic to polymeric structures are beinginvestigated as potential next-generation materials for incorporation in devices for energy conversion and storage as well as for optoelectronic and catalysis applications. The materials are built from C- and N-containing heterocycles with heptazine or triazine rings linked via sp2-bonded N atoms (N(C)3 units) or –NH– groups. The electronic, chemical and optical functionalities are determined by the nature of the local to extended structures as well as the chemical composition of the materials. Because of their typically amorphous to nanocrystalline nature and variable composition, significant challenges remain to fully assess and calibrate the structure–functionality relationships among carbon nitride materials. It is also important to devise a useful and consistent approach to naming the different classes of carbon nitride compounds that accurately describes their chemical and structural characteristics related to their functional performance. Here we evaluate the current state of understanding to highlight key issues in these areas and point out new directions in their development as advanced technological materials.
- Correlation between the proton conductivity and diffusion coefficient of sulfonic acid functionalized chitosan and Nafion composites via impedance spectroscopy measurements. I. Ressam, M. Lahcini, A. Belen Jorge, H Perrot, O. Sel, Ionics, 2017, 23, 2221-2227.
AbstractElectrochemical Impedance Spectroscopy (EIS) was employed to estimate the global transverse proton diffusion coefficient, DH+, in sulfonic acid functionalized sustainable chitosan (CS-SO3H)/Nafion composite films. In contrast to conventional conductivity measurements, EIS measurements were performed at room temperature with a film/liquid interface. In this configuration, the measure of the bulk proton transport is correlated to the DH+ of the membranes which is close to 1.1 × 10−6 cm2 s−1 and 0.33 × 10−6 cm2 s−1 with and without CS-SO3H, respectively. These DH+ values permitted the proton conductivity (σH+) ratio (∼3.9) between the Nafion/CS-SO3H composite and pristine Nafion films to be estimated by using the Nernst-Einstein relationship. This ratio presents a good agreement with that obtained for the σH+ of bulk membranes (∼3.2) measured at 30 °C and 90% RH. The agreement between the σH+ ratios validates our methodology for DH+ estimation by EIS and suggests that the more than three times enhanced σ+H is governed by the ∼3 times higher DH+ in the presence of CS-SO3H.
- Graphitic Carbon Nitride as a Catalyst Support in Fuel Cells and Electrolyzers, Noramalina Mansor, Thomas S Miller, Ishanka Dedigama, Ana Belen Jorge, Jingjing Jia, Veronika Brázdová, Cecilia Mattevi, Chris Gibbs, David Hodgson, Paul R Shearing, Christopher A Howard, Furio Corà, Milo Shaffer, Daniel JL Brett, Paul F McMillan, Electrochim. Acta, 2016, 222, 44-57.
AbstractElectrochemical power sources, such as polymer electrolyte membrane fuel cells (PEMFCs), require the use of precious metal catalysts which are deposited as nanoparticles onto supports in order to minimize their mass loading and therefore cost. State-of-the-art/commercial supports are based on forms of carbon black. However, carbon supports present disadvantages including corrosion in the operating fuel cell environment and loss of catalyst activity. Here we review recent work examining the potential of different varieties of graphitic carbon nitride (gCN) as catalyst supports, highlighting their likely benefits, as well as the challenges associated with their implementation. The performance of gCN and hybrid gCN-carbon materials as PEMFC electrodes is discussed, as well as their potential for use in alkaline systems and water electrolyzers. We illustrate the discussion with examples taken from our own recent studies.For a complete list of publications, please follow this link.