Graphene Cathode Research Articles

Comparison of Waste Volumes on Power Generation and COD Removal in Solid Phase Microbial Fuel Cell (SMFC)

Energy demand rises significantly correlated to human activities in recent years. In contrary, energy supply from unrenewable resource decreases gradually from year to year. OMW as one of the renewable resources has not been expanded well in Indonesia. Therefore, SMFC will answer the alternative technology to generate electricity from OMW. The objectives of this study are conducted to compare of waste volumes on power generation and COD removal in SMFC and determine the optimum waste volume for SMFC application affected by river sediment microorganism source and mixed waste type. SMFC reactor as MFC single chamber was designed by 2.5-liter volume of plastic houseware utilized with single graphene anode and cathode to increase the power generation.The waste volume as the independent variable was adjusted 1/3; 1/2; 2/3 of the 2.5- liter volume of SMFC reactor, whereas river sediment microorganism source and mixed waste were dependent variables. The power density and COD removal percentage in 1/3VR, 1/2VR, and 2/3VR were compared on days 21 which was the typical day of the optimum performance of SMFC. The result shows that power density and COD removal of waste volume 2/3VR was higher than 1/3VR and 1/2VR. Power density of waste volume 2/3VR increased 1.5 - 3 times of power density of waste volume 1/3VR and 1/2VR, respectively. COD removal of waste volume 1/3, 1/2, and 2/3 remained stable. The optimum waste volume, the higher power density and COD removal, in addition to the result that 2/3 of the waste volume was the optimum result.

Low work function Ca doped graphene as a transparent cathode for organic opto-electronics and OLEDs

Graphene is an excellent candidate for a transparent electrode since it has high lateral conductivity and optical transparency, but due to its high work function, between 4.5 and 5eV, it can serve as a good transparent anode but poor transparent cathode due to a barrier for electrons injection. Reducing graphene’s work function is thus essential to make it an ideal transparent cathode as well. Naturally, n-type doping of graphene increases its Fermi level and thus reduces the work function. Among many choices of n-type dopants alkaline element can be good candidate, here we present a study of calcium (Ca) n-doped graphene to be serve as a transparent cathode. Several measurements were carried out on Ca doped graphene and compared them with pristine graphene as a reference, such as: Raman spectroscopy, x-ray photoelectron spectroscopy (XPS) Field effect transistor (FET), transparent electron microscopy (TEM), and photoemission spectroscopy. Our results show that doping graphene with 1 nm of evaporated Ca on the surface reduces its work function by nearly 1eV. We further performed current-voltage characteristics of graphene/Alq3/Ag structures having undoped and doped graphene cathodes. The structures with doped graphene showed an increase of two orders of magnitude in current under the same applied bias due to the contacts barrier reduction. The results confirm the effectiveness of Ca-doped graphene for reducing the barrier for electron injection from graphene to next adjacent organic layer. It demonstrates the feasibility of Ca doped graphene to serve as a transparent cathode in organic devices in general and in OLEDs in particular.

Capacitive charge storage enables an ultrahigh cathode capacity in aluminum-graphene battery

Aluminum-graphene battery is promising for its abundant raw materials, high power density, ultralong cycle life and superior safety. However, the development of aluminum-graphene battery is currently restricted by its insufficient cathode capacity, calling for a newly developed working mechanism. In addition, an irregular constant increase of the cathode capacity was always observed during cycling, but cannot be explained based on the current understanding. Here, we observed an increase of specific capacity by 60% with stable Coulombic efficiency of 98% during 7000 cycles life of Al-graphene batteries employing AlCl3/ET3NHCl electrolyte. We demonstrated this growing cathode capacity is attributed to an increasing contribution of capacitive charge storage during cycling, because a gradually enlarged surface area as capacitive active sites is enabled by the exfoliation of graphitic cathode during the periodic intercalation process. Moreover, the graphene cathode was exfoliated more significantly in AlCl3/ET3NHCl than 1-ethyl-3-methylimidazolium chloride-based electrolyte, which results from the heavier stress on the graphene layers caused by the larger intercalants in AlCl3/ET3NHCl. The common intercalation of cations with AlCl4− clusters was therefore supposed to occur during charging. This new proposed mechanism can offer the new thought for future design on high-capacity cathode of Al-ion battery.

Impulse-Breakdown Characteristics of a High-Power Gas Switch Based on Graphene Cathode

Graphene has attracted great interest for its distinctive band structure and physical properties. Results from previous studies show that a graphene cathode can provide stable field emission and intense emission in a vacuum. In this paper, a graphene cathode was fabricated using chemical vapor deposition (CVD) on copper electrodes, and the breakdown of the cathode in a high-pressure gas was studied. A low-jitter, self-breakdown gas spark switch based on a graphene cathode is proposed in this paper. The impulse-breakdown characteristics of this switch in a quasi-uniform electric field were studied. When the gap length is 5 mm, and the gas pressure is 0.6 MPa, the average breakdown voltage ( $U_{\mathrm {BD}}$ ) is nearly 85.9 kV, and the voltage jitter is only 3.2%; these values are much lower than those for pure copper cathodes and graphite cathodes. The graphene cathode is found to be a suitable choice for use as a high-power gas switch in applications requiring an intense emission source.

C-S Bonds in Sulfur-Embedded Graphene, Carbon Nanotubes, and Flake Graphite Cathodes for Lithium-Sulfur Batteries.

Lithium–sulfur (Li–S) batteries are excellent rechargeable battery candidates which are extraordinarily promising as they exhibit superior specific capacity and well-known energy density; they are cost-effective and environmentally benign. Nevertheless, a few technical issues pose a significant challenge on the path to industrial applications, namely, capacity fade and Coulombic efficiency decay, which are inherent in the soluble polysulfide shuttle effect during charge/discharge cycling. Carbon materials which have excellent conductive scaffold and flexible structure with a variety of morphologies can serve as a remedy to this issue. Herein, with a well-designed melt-diffusion procedure, we prepared three carbon-based sulfur-embedded cathodes with diverse structures [graphene, carbon nanotubes (CNTs), and flake graphite]. Sulfur loading varies between 60 and 73 wt %. Among these three carbon/S cathodes, beyond 100 cycles, the graphene/S cathode showed a discharge capacity of 840 mA h g–1 at 0.2 A g–1 current density and its average Coulombic efficiency was above 99.4%, demonstrating the best cycle stability and reversibility. While at a higher current rate, 1 A g–1, CNT/S reaches the best capacity of 518 mA h g–1 among these three cathodes, revealing excellent sulfur utilization under high rate conditions. The X-ray photo spectroscopy shows evidence for chemical bonding between graphene/CNTs surfaces and carbonyl, hydroxyl, and ether groups, resulting in well-confined polysulfides in the cathode side, which significantly restrain the movement of soluble polysulfide in the charging process and efficiently decreases the capacity fading of sulfur. This unique structure is a potential explanation for the outstanding electrochemical performance.

An Ultra-Fast and Ultra-Stable All-Graphene Lithium Ion Capacitor

Lithium ion capacitors (LICs) are considered as next generation of capacitive energy storage systems , due to their 3~5 times higher energy density than traditional electrochemical double-layer capacitors. However, the battery-type anode inevitably leads to scarified power density and cycling life, due to imbalanced electrochemical performance of two electrodes, which means achieving competitive power density and cycling life simultaneously is an extreme challenge involving in the whole system. We rationally design an ultra-fast and ultra-stable all-graphene LICs, for which various graphene electrode constructions are synthesized orienting in the distinct energy storage principles of two electrodes, and a novel match approach for two electrodes is proposed and applied. Mesoporous graphene (MP-G) cathode is capable to deliver much better high-rate properties and cycling stability, edge carboxyl graphene (G-COOH) anode with expanded graphitic layer spaces enable fast pseudocapacitive and insertion capacity, as well as durability, and an optimal reaction profiles range of G-COOH are systematically determined by a novel quasi-in-situ electrochemical impedance spectroscopy (EIS) to match with MP-G. Thereby, an ultra-fast and ultra-stable LIC system (MP-G//G-COOH) is fabricated and operated in the voltage range of 1.0 ~ 4.2V. As expectedly, MP-G//G-COOH is capable to deliver an ultra-high-power density of 53550 W kg-1and an unprecedented cycling stability of 98.9% retention after 50000 cycles. This result is promising in terms of pushing ultra-fast and ultra-stable LIC system by combining ideal electrode constructions and matching approaches.

Effect of nitrogen doping in the few layer graphene cathode of an aluminum ion battery

We examine the effect of nitrogen dopants in Few-layer graphene (FLG) cathodes on anion intercalation. Different nitrogen dopant configurations within the FLG were achieved by varying the synthesis parameters and their effects are compared. The dopant configurations of the samples were determined via X-ray photoelectron spectroscopy (XPS) and formation energies were calculated using density functional theory, allowing correlation between cell performance and dopant configuration. The reduced ion intercalation within the nitrogen doped FLG, and thus poor charge/discharge characteristics of nitrogen doped FLG cathodes, is attributed to the reduced mobility of the chloroaluminate ions in the presence of nitrogen dopants.

A 4 V Class Potassium Metal Battery with Extremely Low Overpotential.

K metal anodes usually have a low Coulombic efficiency and poor safety owing to their large volume variation and high chemical reactivity. In this study, a three-dimensional K (3D-K) anode is formed by plating metallic K into hollow N-doped C polyhedrons/graphene (HNCP/G). Then a Sn-based solid-electrolyte interphase layer is conformably coated onto the surface of 3D-K to construct Sn@3D-K. Compared with the typical K-foil anode, the Sn@3D-K anode can significantly reduce the interfacial resistance, improve the K+ ion transport mobility, reduce parasitic reactions, and suppress the formation of K dendrites. Meanwhile, HNCP/G serves as a chemically stable, conductive host to accommodate the volume expansion/shrinkage of Sn@3D-K. Owing to these merits, the symmetric Sn@3D-K cell exhibits low voltage hysteresis (9 mV at 0.2 mA cm-2 after 500 h; 31 mV at 1 mA cm-2 after 100 h). When paired with a Prussian blue (PB)/graphene cathode, the K1.56Mn[Fe(CN)6]1.08/G∥Sn@3D-K battery delivers an average discharge plateau of 4.02 V, an ultralow overpotential of 0.01 V, and a high specific capacity of 147.2 mAh g-1, approaching the theoretical value of K2MnFe(CN)6 (156 mAh g-1). A 4 V class K metal battery that exhibits extremely low overpotential and high specific capacity, which are the best among previously reported PB-based K batteries, is proposed.

Synthesis of carbon coated Fe3O4 grown on graphene as effective sulfur-host materials for advanced lithium/sulfur battery

Lithium/sulfur battery (LSB) is considered as one of the most promising battery systems due to its high energy density of 2600 Wh kg−1. Nevertheless, the LSB suffers from some inherent problems that impede its practical application. To circumvent these problems, we grow carbon-coated ferroferric oxide (Fe3O4) nanoparticles on graphene (Fe3O4@C-G) as an effective sulfur host for LSB via a facile hydrothermal method followed by calcination. Highly conductive graphene is utilized to homogeneously deposit the carbon-coated Fe3O4 nanoparticles (Fe3O4@C), which enable rapid and steady long-distance electron transport. Moreover, the carbon coated particles of Fe3O4@C exhibit a developed micro-mesoporous structure, which not only provide space for sulfur loading to prepare a composite Sulfur/carbon-coated Fe3O4 nanoparticles on graphene (S/Fe3O4@C-G) cathode, but also provide channels for the interaction between Fe3O4 and lithium polysulfides. Furthermore, a strong chemical affinity of Fe3O4 nanoparticles coated by micro-mesoporous carbon layers towards polysulfides can be strengthened through the polar-polar interaction. Owning these advantages, the S/Fe3O4@C-G composite cathode deliver a high initial capacity of 1425 mAh g−1 at 0.2 C and maintain a capacity of 1102 mAh g−1 after 100 cycles.

Effect of Anion on the Quantum Capacitance of Graphene Cathode in Lithium Ion Capacitor: A DFT Study

Lithium ion capacitor (LIC) is a kind of electrochemical energy storage device that can combine the power property of a supercapacitor and the energy property of a lithium ion battery simultaneously [1]. Graphene is widely employed as cathode because it can provide excellent capacitance, as well as constructing an effective conducting network [2, 3]. However, the detail understandings of electrode/electrolyte interface in graphene-based LIC is still limited. Based on our previous results, graphene with single vacant defect or pyridinic and pyrrolic doped N atom show much higher quantum capacitance (QC) than the pristine one [4]. This difference can be attributed to the presence of reactive σ state near the Fermi level, which is from the C or N atoms around the defect region. However, when it comes to the real LIC system, reactions may occur between the electrolyte and those reactive atoms in graphene cathode. Therefore, the presence of electrolyte will disturb the density of states (DOS) of graphene-based cathode, and hence the QC and the energy storage ability will vary accordingly. In this work, the interaction between the anion in the electrolyte and graphene cathode with high QC is investigated using First Principle calculation. The results suggest that the defect states of graphene cathode can enhance the adsorption energy towards anion, and hence the QC and electrical double layer (EDL) structure is different with that of pristine graphene cathode. Furthermore, this interaction also decrease the stability of the anion in electrolyte. The results from this work would help to further develop high energy graphene-based LIC and shed some light on its capacity fading mechanisms. Reference: [1] Cericola, et al., Electrochim. Acta, 72(2012), 1. [2] Chen, et al., Energ Environ Sci, 6(2013), 1623. [3] Yu, et al., Nano Energy, 15(2015), 43. [4] Su, et al., Catalysts 8(2018,) 444

Lithium‐Ion Batteries: In Situ Synthesis of Hierarchical Core Double‐Shell Ti‐Doped LiMnPO4@NaTi2(PO4)3@C/3D Graphene Cathode with High‐Rate Capability and Long Cycle Life for Lithium‐Ion Batteries (Adv. Energy Mater. 11/2019)

In article number 1802847 Changzhou Yuan and co-workers report a core double-shell Tidoped LMP@NaTi2(PO4)3@C/three-dimensional graphene (TLMP@NTP@C/3D-G) architecture via in-situ synthetic methodology. Benefiting from synergetic contributions from structural and componential rationales, the integrated TLMP@NTP@C/3D-G cathode yields superior high-rate electrochemical properties for advanced Li-ion batteries (LIBs) as a competitive cathode. More significantly, the electrode design developed here will exert significant impact upon constructing other advanced cathodes for high-energy/power LIBs.

Defect-free soft carbon as cathode material for Al-ion batteries

Al-ion batteries are proposed as promising energy storage candidates for beyond Li-ion technology due to the higher natural earth of Al metal. Recently, various graphite and graphene cathodes for Al-ion batteries have been studied in this regard, but their costs are not satisfactory. In this study, a novel cathode for Al-ion batteries is prepared by graphitizing inexpensive soft carbon materials (mesocarbon microspheres and petroleum coke) at 2800 °C. The charge and discharge process is showcased here for graphitized petroleum coke, which has a storage capacity of 77.7 mAh g−1 with two high discharge voltage (~ 2.25 and 1.80 V), higher than graphitized mesocarbon microspheres (51 mAh g−1). It also has excellent cycle stability and no reduction in specific capacity after 1000 cycles. Affordable cost of the graphitized petroleum coke cathode makes Al-ion battery more promising for large-scale chemical energy storage.

Rapid oxygen diffusive lithium–oxygen batteries using a restacking-inhibited, free-standing graphene cathode film

The rapid oxygen diffusion of corrugated 2D graphene sheets enhances the capacity and cycle life of lithium air batteries.

Metal-free energy storage systems: combining batteries with capacitors based on a methylene blue functionalized graphene cathode

Novel aqueous hybrid ion capacitors based on an MB functionalized graphene cathode and asymmetric electrolytes exhibited both improved energy density and power density.

Boron doped graphene cathode for capacitor via a new one-step method

The graphene cathode was doped with boron via a new and fast method of plasma enhanced chemical vapor deposition (PECVD) at room temperature. Various plasma species of BHx (x = 0–3) with high reactivity reacted with graphene electrode via surface re-reactions and gas-interface intersection. The cathode made of boron doping into graphene (BG) exhibited excellent electrochemical performances in Li-ion capacitors, including a large discharge capacity of 140 mAh g−1 (voltage range: 1.5–4.2 V vs. Li/Li+, current density: 100 mA g−1) and the coulombic efficiency of more than 99.6% within 1000 circles. The capacity, coulombic efficiency and circle performance of the BG electrode were more superior to the undoped graphene electrode owing to the uniform doping of boron plasma species. The PECVD method has the advantages of being simple, is conducted at room-temperature, is time efficient and uniform, thus making it a fast and effective way for doping hetero-atoms into the electrode.

Cover Feature: Enhanced Cycling Performance for Lithium–Sulfur Batteries by a Laminated 2D g‐C3N4/Graphene Cathode Interlayer (ChemSusChem 1/2019)

Cover Feature: Enhanced Cycling Performance for Lithium–Sulfur Batteries by a Laminated 2D g‐C₃N₄/Graphene Cathode Interlayer (ChemSusChem 1/2019)

Flat Monolayer Graphene Cathodes for Li-Oxygen Microbatteries.

Miniature batteries can accelerate the development of mobile electronics by providing sufficient energy to power small devices. Typical microbatteries commonly use thin-film inorganic electrodes based on Li-ion insertion reaction. However, they rely on the complicated thin-film synthesis method of inorganics containing many elements. Graphene, one atomic layer thick carbon sheet, has diverse physical and chemical properties and is compatible with conventional micron-scale device fabrication. Here, we study the use of chemical vapor deposition (CVD) grown monolayer graphene in a two-dimensional configuration, as a future Li-oxygen microbattery cathode. By maximizing the dissolution of discharge intermediates, we obtain 2610 Ah/ggraphene of capacity corresponding to 20% higher areal cathode energy density and 2.7 times higher cathode specific energy than that can be derived from the same volume or mass of conventional Li-ion battery cathode material. Furthermore, a clear observation on the discharge reaction on composite electrodes and their role in the charging reaction was made, thanks to the two-dimensional monolayer graphene Li-oxygen battery cathode. We demonstrate an easy integration of two-dimensional CVD graphene cathode into microscale devices by simply transferring or coating the target device substrate with flexible graphene layers. The ability to integrate and use monolayer graphene on arbitrary device substrates as well as precise control over a chemical derivation of the carbon interface can have a radical impact on future energy-storage devices.

Enhanced Cycling Performance for Lithium-Sulfur Batteries by a Laminated 2D g-C3 N4 /Graphene Cathode Interlayer.

Decay in electrochemical performance resulting from the "shuttle effect" of dissolved lithium polysulfides is one of the biggest obstacles for the realization of practical applications of lithium-sulfur (Li-S) batteries. To meet this challenge, a 2D g-C3 N4 /graphene sheet composite (g-C3 N4 /GS) was fabricated as an interlayer for a sulfur/carbon (S/KB) cathode. It forms a laminated structure of channels to trap polysulfides by physical and chemical interactions. The thin g-C3 N4 /GS interlayer significantly suppresses diffusion of the dissolved polysulfide species (Li2 Sx ; 2<x≤8) from the cathode to the anode, as proven by using an H-type glass cell divided by a g-C3 N4 /GS-coated separator. The S/KB cathode with the g-C3 N4 /GS interlayer (S/KB@C3 N4 /GS) delivers a discharge capacity of 1191.7 mAh g-1 at 0.1 C after 100 cycles, an increase of more than 90 % compared with an S/KB cathode alone (625.8 mAh g-1 ). The S/KB@C3 N4 /GS cathode shows good cycling life, delivering a discharge capacity as high as 612.4 mAh g-1 for 1 C after 1000 cycles. According to XPS results, the anchoring of the g-C3 N4 /GS interlayer to Li2 Sx can be attributed to a coefficient chemical binding effect of g-C3 N4 and graphene on long-chain polysulfides. Generally, the improvement in electrochemical performance originates from a coefficient of the enhanced Li+ diffusion coefficient, increased charge transfer, and the weakening of the shuttle effect of the dissolved Li2 Sx as a result of the g-C3 N4 /GS interlayer.

Carbon-nanotube/sulfur cathode with in-situ assembled Si3N4/graphene interlayer for high-rate and long cycling-life lithium-sulfur batteries

A Si3N4/graphene composite is designed as an interlayer for a carbon-nanotubes/sulfur cathode to improve electrochemical performance of lithium-sulfur batteries. In the interlayer, Si3N4 nanoparticles suppress the migration of the dissolved polysulfides and graphene sheets construct a 3-dimensional charge-transfer network. The carbon-nanotubes/sulfur@Si3N4/graphene cathode delivers an initial discharge capacity of 1334.7 mAh g−1 at 0.1 C and retains a capacity as high as 745.8 mAh g−1 after 200 cycles, with a capacity fade ratio of 0.22% per cycle. The cathode shows good cycling life, delivering a discharge capacity of 413.3 mAh g−1 for 1 C after 1000 cycles. According to the results of density functional theory calculation, the anchoring of the Si3N4/graphene interlayer to lithium polysulfide can be attributed to a coefficient chemical binding of Li-N and Si-S bonds generating from electronic conjugation effect between the Si3N4 supercell surface and the polysulfides. Generally, the improvement in electrochemical performance originates from the enhancements in Li+ diffusion coefficient and charge transfer, and from the restraining of the shuttle effect of the dissolved lithium polysulfide as a result of the Si3N4/graphene interlayer.

Graphene-based quasi-solid-state lithium\u2013oxygen batteries with high energy efficiency and a long cycling lifetime

An aprotic lithium–oxygen battery with an ultrahigh theoretical energy density has attracted significant attention as the next-generation electrochemical energy device demanded by all-electric vehicles and other high-energy devices. Extensive effort has recently been devoted to improving the performances of cathodes, anodes, and electrolytes. However, as an integrated system, the overall battery properties are not determined by the individual components but by the synergy of all components. Despite important progress in the development of cathodes, anodes, and electrolytes, the system-level design and assembly of lithium–oxygen batteries have not benefited from these recent advances. Here, we report a graphene-based quasi-solid-state lithium–oxygen battery consisting of a rationally designed 3D porous graphene cathode, redox mediator-modified gel polymer electrolyte, and porous graphene/Li anode. This integrated prototype battery simultaneously addresses the major challenges of lithium–oxygen batteries and achieves stable cycling at a large capacity, low charge overpotential and high rate in both coin-type and large-scale pouch-type batteries. For the first time, these lithium–oxygen batteries as a whole device deliver gravimetric and volumetric energy densities higher than those of a commercial Li-ion polymer battery. This study represents important progress toward the practical implementation of full-performance lithium–oxygen batteries.