Publications | Anjali Jayakumar

2023

Nature-Based Solution to Eliminate Cyanotoxins in Water Using Biologically Enhanced Biochar

Jane Moore, Anjali Jayakumar, Sylvia Soldatou, and 3 more authors

Environmental Science & Technology, Oct 2023

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Climate change and high eutrophication levels of freshwater sources are increasing the occurrence and intensity of toxic cyanobacterial blooms in drinking water supplies. Conventional water treatment struggles to eliminate cyanobacteria/cyanotoxins, and expensive tertiary treatments are needed. To address this, we have designed a sustainable, nature-based solution using biochar derived from waste coconut shells. This biochar provides a low-cost porous support for immobilizing microbial communities, forming biologically enhanced biochar (BEB). Highly toxic microcystin-LR (MC-LR) was used to influence microbial colonization of the biochar by the natural lake-water microbiome. Over 11 months, BEBs were exposed to microcystins, cyanobacterial extracts, and live cyanobacterial cells, always resulting in rapid elimination of toxins and even a 1.6–1.9 log reduction in cyanobacterial cell numbers. After 48 h of incubation with our BEBs, the MC-LR concentrations dropped below the detection limit of 0.1 ng/mL. The accelerated degradation of cyanotoxins was attributed to enhanced species diversity and microcystin-degrading microbes colonizing the biochar. To ensure scalability, we evaluated BEBs produced through batch-scale and continuous-scale pyrolysis, while also guaranteeing safety by maintaining toxic impurities in biochar within acceptable limits and monitoring degradation byproducts. This study serves as a proof-of-concept for a sustainable, scalable, and safe nature-based solution for combating toxic algal blooms.
@article{doi:10.1021/acs.est.3c05298, author = {Moore, Jane and Jayakumar, Anjali and Soldatou, Sylvia and Mašek, Ondřej and Lawton, Linda A and Edwards, Christine}, title = {Nature-Based Solution to Eliminate Cyanotoxins in Water Using Biologically Enhanced Biochar}, journal = {Environmental Science \& Technology}, volume = {0}, number = {0}, pages = {null}, month = oct, year = {2023}, doi = {10.1021/acs.est.3c05298}, https://doi.org/10.1021/acs.est.3c05298 }, eprint = { https://doi.org/10.1021/acs.est.3c05298 }, }
Unlocking the Power of Woody and Non-Woody Biochar: Maximising Supercapacitor Performance Through Feedstock and Activation Treatment Selection

Jiacheng Sun, Anjali Jayakumar, Carlos Díaz-Maroto, and 3 more authors

Aug 2023

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This study investigates the influence of feedstocks and activation methods on the electrochemical properties of activated biochars, which are promising electrode materials for energy storage devices. Two categories of lignocellulosic biomasses (woody and non-woody) and three activation methods (CO2, steam, and KOH) were used to produce biochars, and the physicochemical and electrochemical properties were evaluated. The results showed that biochars derived from non-woody had higher specific capacitance than woody biochars, despite lower electrical conductivity and porosity. Chemical activation was found to increase volatile matter and porosity of the biochar material, resulting in improved electrochemical performance compared to physical activation. However, chemical activation can cause low electrical conductivity. KOH activated Miscanthus straw pellet biochar exhibited best specific capacitance of 468 F g-1. The study highlights the importance of carefully selecting the feedstocks and activation methods to optimise the electrochemical properties of biochar for potential commercial use as a sustainable supercapacitor material.
@misc{sun_unlocking_2023, address = {Rochester, NY}, type = {{SSRN} {Scholarly} {Paper}}, title = {Unlocking the {Power} of {Woody} and {Non}-{Woody} {Biochar}: {Maximising} {Supercapacitor} {Performance} {Through} {Feedstock} and {Activation} {Treatment} {Selection}}, shorttitle = {Unlocking the {Power} of {Woody} and {Non}-{Woody} {Biochar}}, doi = {10.2139/ssrn.4556356}, language = {en}, urldate = {2023-09-05}, author = {Sun, Jiacheng and Jayakumar, Anjali and Díaz-Maroto, Carlos and Moreno, Inés and Fermoso, Javier and Mašek, Ondřej}, month = aug, year = {2023}, keywords = {Agriculture waste, Biochar, Supercapacitor, Activation, Carbon material}, }
Systematic evaluation of pyrolysis processes and biochar quality in the operation of low-cost flame curtain pyrolysis kiln for sustainable biochar production

Anjali Jayakumar, David Morrisset, Vasileios Koutsomarkos, and 5 more authors

Current Research in Environmental Sustainability, Aug 2023

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Low-cost pyrolysis units such as flame curtain pyrolysis kilns are gaining popularity for biochar production. However, the processes that govern the working of such units are not well understood. Here, emissions, temperatures and mass loss are monitored in real-time during kiln operation, followed by extensive biochar sampling. We found that by adjusting the layering rates of feedstock during kiln operation, we can obtain a biochar yield (28 wt% with a fixed carbon content of 65 wt%) comparable to that produced from the same feedstock in a continuous-scale pyrolysis unit, highlighting the importance of systematic guidelines for optimal kiln operation.
@article{JAYAKUMAR2023100213, title = {Systematic evaluation of pyrolysis processes and biochar quality in the operation of low-cost flame curtain pyrolysis kiln for sustainable biochar production}, journal = {Current Research in Environmental Sustainability}, volume = {5}, pages = {100213}, year = {2023}, issn = {2666-0490}, doi = {10.1016/j.crsust.2023.100213}, author = {Jayakumar, Anjali and Morrisset, David and Koutsomarkos, Vasileios and Wurzer, Christian and Hadden, Rory M. and Lawton, Linda and Edwards, Christine and Mašek, Ondřej}, keywords = {Flame curtain pyrolysis, Low-cost homogeneous biochar, Combustion science, Emissions, Operating guidelines} }

2022

Chapter 24 - Sequential biochar systems in a circular economy

Christian Wurzer, Anjali Jayakumar, and Ondřej Mašek

In Biochar in Agriculture for Achieving Sustainable Development Goals, Aug 2022

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Despite the immense development of biochar technology during the last decade, we still await its widespread adoption in agriculture and beyond. Current obstacles for biochar are based on limited economic attractiveness arising from its dual nature as a renewable, multifunctional material in competition with fossil-based, single-use alternatives, and its parallel purpose as a carbon negative emission technology. While the combination of these properties makes biochar unique, monetising these double benefits presents difficulties. In this chapter, we evaluate the perception of biochar as a product and identify intrinsic problems of underlying concepts. Sequential biochar systems are introduced as a novel utilization strategy, based on the identification of biochar as a carrier for environmental services rather than a product. The proposed service-oriented concept enables changes in biochar’s pricing mechanism and increases its economic competitiveness without the need for further improvements in production or application. Recycling of biochar is used as a novel way to utilize biochar’s multifunctional properties while connecting different industrial sectors and resource streams. We discuss the transformation and transfer of resources with biochar, the integration of sequential biochar systems into circular economy concepts, and arising synergies from this novel area of research. Two examples of sequential biochar systems, based in an industrial and an agrarian context, are proposed and explained in detail.
@incollection{WURZER2022305, title = {Chapter 24 - Sequential biochar systems in a circular economy}, editor = {Tsang, Daniel C.W. and Ok, Yong Sik}, booktitle = {Biochar in Agriculture for Achieving Sustainable Development Goals}, publisher = {Academic Press}, pages = {305-319}, year = {2022}, isbn = {978-0-323-85343-9}, doi = {10.1016/B978-0-323-85343-9.00016-1}, author = {Wurzer, Christian and Jayakumar, Anjali and Mašek, Ondřej}, keywords = {Biochar systems, biochar economics, recycling, circular economy, resource recovery, carbon sequestration} }

2021

Modulation of Single Atomic Co and Fe Sites on Hollow Carbon Nanospheres as Oxygen Electrodes for Rechargeable Zn–Air Batteries

Vishal Jose, Huimin Hu, Eldho Edison, and 9 more authors

Small Methods, Aug 2021

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Abstract Efficient bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are required for metal air batteries, to replace costly metals, such as Pt and Ir/Ru based compounds, which are typically used as benchmarks for ORR and OER, respectively. Isolated single atomic sites coordinated with nitrogen on carbon supports (M-N-C) have promising performance for replacement of precious metal catalysts. However, most of monometallic M-N-C catalysts demonstrate unsatisfactory bifunctional performance. Herein, a facile way of preparing bimetallic Fe and Co sites entrapped in nitrogen-doped hollow carbon nanospheres (Fe,Co-SA/CS) is explored, drawing on the unique structure and pore characteristics of Zeolitic imidazole frameworks and molecular size of Ferrocene, an Fe containing species. Fe,Co-SA/CS showed an ORR onset potential and half wave potential of 0.96 and 0.86 V, respectively. For OER, (Fe,Co)-SA/CS attained its anodic current density of 10 mA cm–2 at an overpotential of 360 mV. Interestingly, the oxygen electrode activity (ΔE) for (Fe,Co)-SA/CS and commercial Pt/C-RuO2 is calculated to be 0.73 V, exhibiting the bifunctional catalytic activity of (Fe,Co)-SA/CS. (Fe,Co)-SA/CS evidenced desirable specific capacity and cyclic stability than Pt/C-RuO2 mixture when utilized as an air cathode in a homemade Zinc-air battery.
@article{https://doi.org/10.1002/smtd.202000751, author = {Jose, Vishal and Hu, Huimin and Edison, Eldho and Manalastas Jr., William and Ren, Hao and Kidkhunthod, Pinit and Sreejith, Sivaramapanicker and Jayakumar, Anjali and Nsanzimana, Jean Marie Vianney and Srinivasan, Madhavi and Choi, Jinho and Lee, Jong-Min}, title = {Modulation of Single Atomic Co and Fe Sites on Hollow Carbon Nanospheres as Oxygen Electrodes for Rechargeable Zn–Air Batteries}, journal = {Small Methods}, volume = {5}, number = {2}, pages = {2000751}, keywords = {single atoms, oxygen electrocatalysis, zinc–air battery}, doi = {10.1002/smtd.202000751}, year = {2021} }
New directions and challenges in engineering biologically-enhanced biochar for biological water treatment

Anjali Jayakumar, Christian Wurzer, Sylvia Soldatou, and 3 more authors

Science of The Total Environment, Aug 2021

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Cost-effective, efficient, and sustainable water treatment solutions utilising existing materials and technology will make it easier for low and middle-income countries to adopt them, improving public health. The ability of biochar to mediate and support microbial degradation of contaminants, combined with its carbon-sequestration potential, has attracted attention in recent years. Biochar is a possible candidate for use in cost-effective and sustainable biological water treatment, especially in agrarian economies with easy access to abundant biomass in the form of crop residues and organic wastes. This review evaluates the scope, potential benefits (economic and environmental) and challenges of sustainable biological water treatment using ‘Biologically-Enhanced Biochar’ or BEB. We discuss the various processes occurring in BEB systems and demonstrate the urgent need to investigate microbial degradation mechanisms. We highlight the need to correlate biochar properties to biofilm development, which can eventually determine process efficiency. We also demonstrate the various opportunities in adopting BEB as a cheaper and more viable alternative in Low and Middle Income Countries and compare it to the current benchmark, ‘Biological Activated Carbon’. We focus on the recent advances in the areas of data science, mathematical modelling and molecular biology to systematically and sustainably design BEB filters, unlike the largely empirical design approaches seen in water treatment. ‘Sequential biochar systems’ are introduced as specially designed end-of-life techniques to lower the environmental impact of BEB filters and examples of their integration into biological water treatment that can fulfil zero waste criteria for BEBs are given.
@article{JAYAKUMAR2021148977, title = {New directions and challenges in engineering biologically-enhanced biochar for biological water treatment}, journal = {Science of The Total Environment}, volume = {796}, pages = {148977}, year = {2021}, issn = {0048-9697}, doi = {10.1016/j.scitotenv.2021.148977}, author = {Jayakumar, Anjali and Wurzer, Christian and Soldatou, Sylvia and Edwards, Christine and Lawton, Linda A. and Mašek, Ondřej}, keywords = {Biologically-enhanced biochar, Biological water treatment, Biochar-microbial interactions, Sequential biochar systems} }

2020

Hydrogels for Medical and Environmental Applications

Anjali Jayakumar, Vishal K. Jose, and Jong-Min Lee

Small Methods, Aug 2020

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Abstract Hydrogels are heavily-hydrated 3D microliths having loose, porous structures. Unlike organogels, elastomers, and carbohydrates, hydrogels are structures with water as a continuous phase/solvent. Being water-based, they provide a lot of scope for facile improvizations in their structure and in introducing chemical functionalities. They can house various functional materials in their highly porous networks, making them potential candidates for diverse applications. Various possibilities in using different starting materials for hydrogels are described herein, and it is shown how choosing and optimizing these components that make up the hydrogel can modify their properties. Studying hydrogels and their formulations will enable the understanding of their multifunctional properties. External stimuli-responsive and functional systems can be designed out of these microliths to suit a wide range of applications like biosensing, cancer therapy, regenerative medicine, drug delivery, environmental parameter sensing, water desalination, heavy-metal adsorption, and water treatment. Environmental degradation is occurring at an alarming rate, cascading the adverse effects on the environment but also causing detrimental effects in public health. In this review, multiple perspectives from state-of-the-art literature are brought together to examine hydrogels as very powerful, sustainable, cost-effective, and simple solutions for the betterment of the environment and subsequently, public health.
@article{https://doi.org/10.1002/smtd.201900735, author = {Jayakumar, Anjali and Jose, Vishal K. and Lee, Jong-Min}, title = {Hydrogels for Medical and Environmental Applications}, journal = {Small Methods}, volume = {4}, number = {3}, pages = {1900735}, keywords = {biosensing, chemical sensing, drug delivery, hydrogels, public health, regenerative medicine, water remediation}, doi = {10.1002/smtd.201900735}, year = {2020} }
Biochar characterization methods

Ondřej Mašek, Anna Bogush, Anjali Jayakumar, and 2 more authors

Aug 2020

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This chapter will focus on reviewing some of the most commonly used characterization techniques, highlighting their main areas of application, as well as discussing potential challenges and limitations. In addition, selected advanced characterization methods and methods relevant to emerging biochar applications will also be introduced.While the aim of the chapter is not to provide an exhaustive introduction and discussion of all possible ways to characterize biochar in all its aspects, it will provide readers with useful pointers to navigate this complex area.
@incollection{10.1088/978-0-7503-2660-5ch5, author = {Mašek, Ondřej and Bogush, Anna and Jayakumar, Anjali and Wurzer, Christian and Peters, Clare}, title = {Biochar characterization methods}, booktitle = {Biochar}, publisher = {IOP Publishing}, year = {2020}, series = {2053-2563}, type = {Book Chapter}, pages = {5-1 to 5-19}, doi = {10.1088/978-0-7503-2660-5ch5}, isbn = {978-0-7503-2660-5} }
Safe water for all: A nature-based approach for cyanotoxin elimination from potable water

Sylvia Soldatou, Anjali Jaykumar, Abeysiri H.A.S.N, and 4 more authors

Aug 2020

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Cyanobacterial blooms are a serious threat to public health and water quality due to the production of cyanotoxins as a result of nutrient pollution from industry, agriculture, domestic waste as well as global warming. The microcystins (MCs) are the most abundant cyanotoxins consisting of >200 analogues causing both acute and chronic toxicity, sometimes resulting in death. In Asian countries, such as Sri Lanka, reports of kidney disease are constantly increasing. Although no direct link between metal and pesticide contamination in water and kidney disease has been found, high concentration of cyanobacteria cells in drinking water wells implies that the nephrotoxic effects of cyanotoxins might play a key factor in the reports of Chronic Kidney Disease of unknown aetiology (CKDu) in Sri Lanka. Therefore, we propose a nature-based approach for water treatment which will study the hypotheses that cyanotoxins can cause CKDu. Sri Lankan bacterial isolates (Alcaligens sp., Roseateles sp., Bacillus sp., and Micrococcus sp.) known to degrade microcystins, were used to form biofilm on biochar from Sri Lankan crop residues, such as coconut shells. The immobilisation of the microbes was assessed via a high-throughput colourimetric assay, followed by monitoring the biodegradation rate of microcystins when added to the immobilised cultures. Biodegradation products were analysed and identified through molecular networking and quantified via LC-MS/MS. Ultimately, this project will provide safe water in line with UN Sustainable Development Goal 6.1 as well contributing in sustainable goals 7 (Affordable and Clean Energy), 11 (Sustainable Cities and Communities) and 12 (Responsible Production and Consumption).
@article{mbs:/content/journal/acmi/10.1099/acmi.ac2020.po0574, author = {Soldatou, Sylvia and Jaykumar, Anjali and H.A.S.N, Abeysiri and M. Manage, Pathmalal and Mašek, Ondřej and A. Lawton, Linda and Edwards, Christine}, title = {Safe water for all: A nature-based approach for cyanotoxin elimination from potable water}, journal = {Access Microbiology}, year = {2020}, volume = {2}, number = {7A}, doi = {10.1099/acmi.ac2020.po0574}, publisher = {Microbiology Society}, issn = {2516-8290}, type = {Journal Article}, eid = {676} }

2019

Bimetal/Metal Oxide Encapsulated in Graphitic Nitrogen Doped Mesoporous Carbon Networks for Enhanced Oxygen Electrocatalysis

Vishal Jose, Anjali Jayakumar, and Jong-Min Lee

ChemElectroChem, Aug 2019

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Abstract In this study, Fe doped, Co and CoO encapsulated N doped carbon frameworks were prepared from simple hybrid zeolite imidazole frameworks (ZIF) with extra N enrichment. The facile strategy included preparation of ZIF-8 core and ZIF-67 shell and later replacing the metal centers of ZIF with Fe ions and increasing the N content with N rich melamine. The metal and metal oxide components got captured and encapsulated in the N doped mesoporous carbon frameworks through a pyrolysis process at different temperatures. Fe, Co and CoO were trapped in the N doped mesoporous carbon networks through annealing and denoted as FCNCx. The activity and electrochemical stability of such prepared materials towards ORR and OER were tested in basic media. After analyzing rotating disk electrode studies, FCNC900 was seen to perform superior bifunctional electrocatalytic performance for both ORR and OER which was higher than Pt/C catalyst. Promising ORR performance of FCNC900 can be simply be judged from E1/2=0.868 V (vs. RHE) and Eonset=1.01 V (vs. RHE) while OER overpotential for same catalyst was 360 mV much smaller than others. Longer stability and high methanol tolerance of this catalyst was also investigated.
@article{https://doi.org/10.1002/celc.201801508, author = {Jose, Vishal and Jayakumar, Anjali and Lee, Jong-Min}, title = {Bimetal/Metal Oxide Encapsulated in Graphitic Nitrogen Doped Mesoporous Carbon Networks for Enhanced Oxygen Electrocatalysis}, journal = {ChemElectroChem}, volume = {6}, number = {5}, pages = {1485-1491}, keywords = {bifunctional electrocatalysts, metal/metaloxide, N-doped carbon, oxygen reduction reaction, oxygen evolution}, doi = {10.1002/celc.201801508}, year = {2019} }

2018

Bifunctional Sulfonated MoO3–ZrO2 Binary Oxide Catalysts for the One-Step Synthesis of 2,5-Diformylfuran from Fructose

Jun Zhao, Anjali Jayakumar, and Jong-Min Lee

ACS Sustainable Chemistry & Engineering, Aug 2018

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Sulfonated MoO3–ZrO2 binary oxides (MZS) with different Mo/Zr ratios were synthesized and applied as bifunctional catalysts for the simple one-pot transformation of fructose to 2,5-diformylfuran (DFF). The presence of Brønsted acid sites and the molybdenum oxide species in the catalysts is responsible for the high efficiency and good activity of the catalysts. The former contributes to a high yield of 5-hydroxymethylfurfural (HMF) in the fructose dehydration, and the latter has the role of catalyzing the selective aerobic oxidation of the resulted HMF into DFF. In optimized reaction conditions, DFF yield of 74% with fructose of 100% can be achieved in a one-step reaction. The catalyst can be separated, simply regenerated, and reused without any significant loss in activity, indicating its great potential for the industrial mass production of DFF from fructose.
@article{doi:10.1021/acssuschemeng.7b02671, author = {Zhao, Jun and Jayakumar, Anjali and Lee, Jong-Min}, title = {Bifunctional Sulfonated MoO3–ZrO2 Binary Oxide Catalysts for the One-Step Synthesis of 2,5-Diformylfuran from Fructose}, journal = {ACS Sustainable Chemistry \& Engineering}, volume = {6}, number = {3}, pages = {2976-2982}, year = {2018}, doi = {10.1021/acssuschemeng.7b02671}, eprint = {https://doi.org/10.1021/acssuschemeng.7b02671}, }
MoO3-Containing Protonated Nitrogen Doped Carbon as a Bifunctional Catalyst for One-Step Synthesis of 2,5-Diformylfuran from Fructose

Jun Zhao, Anjali Jayakumar, Zhong-Ting Hu, and 3 more authors

ACS Sustainable Chemistry & Engineering, Aug 2018

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Fabricating 3D Macroscopic Graphene-Based Architectures with Outstanding Flexibility by the Novel Liquid Drop/Colloid Flocculation Approach for Energy Storage Applications

Meng Han, Anjali Jayakumar, Zongheng Li, and 9 more authors

ACS Applied Materials & Interfaces, Aug 2018

PMID: 29939002

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Inspired by “water ripples” in nature and the flocculation phenomenon in colloid chemistry, a novel liquid drop/colloid flocculation approach is developed to fabricate an extremely flexible and compressible 3D macroscopic graphene-based architecture (hydrogels or aerogels), via a new coagulation-induced self-assembly mechanism. This facile and universal technique can be achieved in a neutral, acidic, or basic coagulation bath, producing microsized hydrogels with various structures, such as mushroom, circle, disc shapes, etc. The method also allows us to introduce various guest materials in the graphene matrix using transition metal salts as the coagulating bath. A mushroom-shaped NiCo oxide/GS hybrid aerogel (diameter: 3 mm) is prepared as an example, with ultrathin NiCo oxide nanosheets in situ grown onto the surface of graphene. By employing as binder-free electrodes, these hybrid aerogels exhibit a specific capacitance of 858.3 F g–1 at 2 A g–1, as well as a good rate capability and cyclic stability. The asymmetric supercapacitor, assembling with the hybrid aerogels as cathode and graphene hydrogels as anode materials, could deliver an energy density of 21 Wh kg–1 at power density of 4500 W kg–1. The ease of synthesis and the feasibility of obtaining highly flexible aerogels with varied morphologies and compositions make this method a promising one for use in the field of biotechnology, electrochemistry, flexible electronics, and environment applications.
@article{doi:10.1021/acsami.8b02942, author = {Han, Meng and Jayakumar, Anjali and Li, Zongheng and Zhao, Qiannan and Zhang, Junming and Jiang, Xiaoping and Guo, Xiaolong and Wang, Ronghua and Xu, Chaohe and Song, Shufeng and Lee, Jong-Min and Hu, Ning}, title = {Fabricating 3D Macroscopic Graphene-Based Architectures with Outstanding Flexibility by the Novel Liquid Drop/Colloid Flocculation Approach for Energy Storage Applications}, journal = {ACS Applied Materials \& Interfaces}, volume = {10}, number = {26}, pages = {21991-22001}, year = {2018}, doi = {10.1021/acsami.8b02942}, note = {PMID: 29939002}, eprint = {https://doi.org/10.1021/acsami.8b02942} }
A Coconut Leaf Sheath Derived Graphitized N-Doped Carbon Network for High-Performance Supercapacitors

Anjali Jayakumar, Jun Zhao, and Jong-Min Lee

ChemElectroChem, Aug 2018

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Abstract A highly graphitized nitrogen-doped carbon network is synthesized from biomass, obtained from coconut tree leaf sheath and successfully demonstrates high energy storage properties for use in supercapacitors. A simple thermal physical activation in carbon dioxide atmosphere also enables the electrochemical activity of the carbon to be improved. A detailed study is carried out to understand the dependence of the electrochemical performance on parameters such as the concentration of urea used for doping, the activation temperature, and time of activation. An optimized sample is obtained to give a very high electrochemical performance. Our best sample, obtained by using a 0.5 M urea solution for doping, annealed at 700 °C under a N2 atmosphere and activated at an activation temperature of 800 °C under a CO2 atmosphere, named 0.5 M-700 N-800C, gave a very high specific capacitance of 360.9 F g−1 in 2 M KOH in the potential window of 0 to −1.1 V. This performance as a negative electrode exceeds the specific capacitance of graphene hydrogels (305 F g−1) that we prepared and is more than that of commercially available activated carbon 218.18 F g−1. Thus, it brings to light the possibility of using our material as an efficient, cheap substitute for negative electrode materials like graphene, carbon nanotubes, and activated carbon. This process is facile, extremely cheap, and environmental friendly, which utilizes urea, a non-hazardous nitrogen dopant.
@article{https://doi.org/10.1002/celc.201701133, author = {Jayakumar, Anjali and Zhao, Jun and Lee, Jong-Min}, title = {A Coconut Leaf Sheath Derived Graphitized N-Doped Carbon Network for High-Performance Supercapacitors}, journal = {ChemElectroChem}, volume = {5}, number = {2}, pages = {284-291}, keywords = {coconut leaf sheath, biomass-derived, negative electrode, supercapacitors}, doi = {10.1002/celc.201701133}, year = {2018} }

Carbon-based nanomaterial hybrids energy storage applications

Anjali Jayakumar

Nanyang Technological University, Aug 2018

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@phdthesis{jayakumar_carbon-based_2018,
  title = {Carbon-based nanomaterial hybrids energy storage applications},
  urldate = {2023-09-05},
  school = {Nanyang Technological University},
  author = {Jayakumar, Anjali},
  year = {2018},
  doi = {10.32657/10220/47651}
}

2017

MOF-Derived Hollow Cage NixCo3−xO4 and Their Synergy with Graphene for Outstanding Supercapacitors

Anjali Jayakumar, Rajini P. Antony, Ronghua Wang, and 1 more author

Small, Aug 2017

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Highly optimized nickel cobalt mixed oxide has been derived from zeolite imidazole frameworks. While the pure cobalt oxide gives only 178.7 F g−1 as the specific capacitance at a current density of 1 A g−1, the optimized Ni:Co 1:1 has given an extremely high and unprecedented specific capacitance of 1931 F g−1 at a current density of 1 A g−1, with a capacitance retention of 69.5% after 5000 cycles in a three electrode test. This optimized Ni:Co 1:1 mixed oxide is further used to make a composite of nickel cobalt mixed oxide/graphene 3D hydrogel for enhancing the electrochemical performance by virtue of a continuous and porous graphene conductive network. The electrode made from GNi:Co 1:1 successfully achieves an even higher specific capacitance of 2870.8 F g−1 at 1 A g−1 and also shows a significant improvement in the cyclic stability with 81% capacitance retention after 5000 cycles. An asymmetric supercapacitor is also assembled using a pure graphene 3D hydrogel as the negative electrode and the GNi:Co 1:1 as the positive electrode. With a potential window of 1.5 V and binder free electrodes, the capacitor gives a high specific energy density of 50.2 Wh kg−1 at a high power density of 750 W kg−1.
@article{https://doi.org/10.1002/smll.201603102, author = {Jayakumar, Anjali and Antony, Rajini P. and Wang, Ronghua and Lee, Jong-Min}, title = {MOF-Derived Hollow Cage NixCo3−xO4 and Their Synergy with Graphene for Outstanding Supercapacitors}, journal = {Small}, volume = {13}, number = {11}, pages = {1603102}, keywords = {asymmetric supercapacitors, energy storage, graphene, nickel cobalt mixed oxide, optimization}, doi = {10.1002/smll.201603102}, year = {2017} }
MOF-Derived Hollow Cage NixCo3−xO4 and Their Synergy with Graphene for Outstanding Supercapacitors

Anjali Jayakumar, Rajini P. Antony, Ronghua Wang, and 1 more author

Small, Aug 2017

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Highly optimized nickel cobalt mixed oxide has been derived from zeolite imidazole frameworks. While the pure cobalt oxide gives only 178.7 F g−1 as the specific capacitance at a current density of 1 A g−1, the optimized Ni:Co 1:1 has given an extremely high and unprecedented specific capacitance of 1931 F g−1 at a current density of 1 A g−1, with a capacitance retention of 69.5% after 5000 cycles in a three electrode test. This optimized Ni:Co 1:1 mixed oxide is further used to make a composite of nickel cobalt mixed oxide/graphene 3D hydrogel for enhancing the electrochemical performance by virtue of a continuous and porous graphene conductive network. The electrode made from GNi:Co 1:1 successfully achieves an even higher specific capacitance of 2870.8 F g−1 at 1 A g−1 and also shows a significant improvement in the cyclic stability with 81% capacitance retention after 5000 cycles. An asymmetric supercapacitor is also assembled using a pure graphene 3D hydrogel as the negative electrode and the GNi:Co 1:1 as the positive electrode. With a potential window of 1.5 V and binder free electrodes, the capacitor gives a high specific energy density of 50.2 Wh kg−1 at a high power density of 750 W kg−1.
@article{https://doi.org/10.1002/smll.201603103, author = {Jayakumar, Anjali and Antony, Rajini P. and Wang, Ronghua and Lee, Jong-Min}, title = {MOF-Derived Hollow Cage NixCo3−xO4 and Their Synergy with Graphene for Outstanding Supercapacitors}, journal = {Small}, volume = {13}, number = {11}, pages = {1603102}, keywords = {asymmetric supercapacitors, energy storage, graphene, nickel cobalt mixed oxide, optimization}, doi = {10.1002/smll.201603102}, year = {2017} }
Cr-MIL-101-Encapsulated Keggin Phosphomolybdic Acid as a Catalyst for the One-Pot Synthesis of 2,5-Diformylfuran from Fructose

Jun Zhao, Jayakumar Anjali, Yibo Yan, and 1 more author

ChemCatChem, Aug 2017

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Abstract The conversion of fructose into 2,5-diformylfuran (DFF) is a tandem reaction that consists of the dehydration of fructose to 5-hydroxymethylfurfural (HMF) catalyzed by an acid catalyst and subsequent oxidation of HMF to DFF by a redox catalyst. Phosphomolybdic acid encapsulated in MIL-101 (PMA–MIL-101), with high Brønsted acidity and moderate redox potential, was evaluated as a promising catalyst for the one-pot synthesis of DFF directly from fructose. The results demonstrated that PMA–MIL-101 was an efficient and recyclable bifunctional catalyst for the production of DFF from fructose in DMSO; it showed high activity and selectivity towards the direct transformation of fructose into DFF, and it could be reused. A satisfactory DFF yield of 75.1 % was obtained over 2 PMA–MIL-101 in a one-pot, one-step reaction under optimal reaction conditions.
@article{https://doi.org/10.1002/cctc.201601546, author = {Zhao, Jun and Anjali, Jayakumar and Yan, Yibo and Lee, Jong-Min}, title = {Cr-MIL-101-Encapsulated Keggin Phosphomolybdic Acid as a Catalyst for the One-Pot Synthesis of 2,5-Diformylfuran from Fructose}, journal = {ChemCatChem}, volume = {9}, number = {7}, pages = {1187-1191}, keywords = {acidity, biomass, carbohydrates, dehydration, metal–organic frameworks}, doi = {10.1002/cctc.201601546}, year = {2017} }

2016

Ni(OH)2 Nanoflowers/Graphene Hydrogels: A New Assembly for Supercapacitors

Ronghua Wang, Anjali Jayakumar, Chaohe Xu, and 1 more author

ACS Sustainable Chemistry & Engineering, Aug 2016

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A novel structure of graphene-based hybrid hydrogels was constructed, in which α-Ni(OH)2 nanoflowers with nanopetals thicknesses of approximately 20 nm were uniformly anchored on a three-dimensional graphene framework. Benefiting from the unique morphological nickel hydroxide nanoflowers and hydrogels, the nickel hydroxide nanoflowers/graphene hydrogels exhibited great specific capacitances (1 A·g–1; 1632 F·g–1), great rate capabilities, and longer cycle life (after 1000 cycles, 95.2% capacitance retention) when used as electrodes in supercapacitors.
@article{doi:10.1021/acssuschemeng.6b00362, author = {Wang, Ronghua and Jayakumar, Anjali and Xu, Chaohe and Lee, Jong-Min}, title = {Ni(OH)2 Nanoflowers/Graphene Hydrogels: A New Assembly for Supercapacitors}, journal = {ACS Sustainable Chemistry \& Engineering}, volume = {4}, number = {7}, pages = {3736-3742}, year = {2016}, doi = {10.1021/acssuschemeng.6b00362}, eprint = {https://doi.org/10.1021/acssuschemeng.6b00362}, }
Ni(OH)2 Nanoflowers/Graphene Hydrogels: A New Assembly for Supercapacitors

Ronghua Wang, Anjali Jayakumar, Chaohe Xu, and 1 more author

ACS Sustainable Chemistry & Engineering, Aug 2016

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A novel structure of graphene-based hybrid hydrogels was constructed, in which α-Ni(OH)2 nanoflowers with nanopetals thicknesses of approximately 20 nm were uniformly anchored on a three-dimensional graphene framework. Benefiting from the unique morphological nickel hydroxide nanoflowers and hydrogels, the nickel hydroxide nanoflowers/graphene hydrogels exhibited great specific capacitances (1 A·g–1; 1632 F·g–1), great rate capabilities, and longer cycle life (after 1000 cycles, 95.2% capacitance retention) when used as electrodes in supercapacitors.
@article{doi:10.1021/acssuschemeng.6b00363, author = {Wang, Ronghua and Jayakumar, Anjali and Xu, Chaohe and Lee, Jong-Min}, title = {Ni(OH)2 Nanoflowers/Graphene Hydrogels: A New Assembly for Supercapacitors}, journal = {ACS Sustainable Chemistry \& Engineering}, volume = {4}, number = {7}, pages = {3736-3742}, year = {2016}, doi = {10.1021/acssuschemeng.6b00362}, eprint = {https://doi.org/10.1021/acssuschemeng.6b00362} }

2015

Novel graphene/polyaniline/MnOx 3D-hydrogels obtained by controlled morphology of MnOx in the graphene/polyaniline matrix for high performance binder-free supercapacitor electrodes

Anjali Jayakumar, Yong-Jin Yoon, Ronghua Wang, and 1 more author

RSC Adv., Aug 2015

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A novel three dimensional ternary composite graphene-based hydrogel was prepared using a simple hydrothermal reaction. The graphene/polyaniline/MnOx hydrogel named as PGM-HCl, obtained by the controlled morphology of MnOx by preparing it in an acidic environment using hydrochloric acid (HCl), offered an extremely high specific capacitance of 955 F g−1 at a current density of 1 A g−1 and a capacitance retention of 89% after 1000 cycles and 69.1% after 5000 cycles at 20 A g−1. The synergistic effects created by the pseudocapacitance of PANI, MnOx and the electrochemical double layer capacitance of graphene highly improved the overall electrochemical performance of these hydrogels compared to the performances of the individual constituents. The electrode prepared from this material gave an extremely high specific energy density of 61.2 W h kg−1 even at a high power density of 4.5 kW kg−1. The composite had the superior advantage of being used directly for binder free supercapacitor electrodes and made use of low cost raw materials making it a very promising candidate for cost effective, large scale and high energy applications. A hydrogel PGM was also prepared in the absence of HCl using a purely hydrothermal reaction under the same reaction conditions, for comparison. Thus, this study opens the exciting untapped potential in engineering and synthesizing such composites with existing low cost materials for high performance energy storage devices like supercapacitors.
@article{C5RA16884H, author = {Jayakumar, Anjali and Yoon, Yong-Jin and Wang, Ronghua and Lee, Jong-Min}, title = {Novel graphene/polyaniline/MnOx 3D-hydrogels obtained by controlled morphology of MnOx in the graphene/polyaniline matrix for high performance binder-free supercapacitor electrodes}, journal = {RSC Adv.}, year = {2015}, volume = {5}, issue = {114}, pages = {94388-94396}, publisher = {The Royal Society of Chemistry}, doi = {10.1039/C5RA16884H}, }