Carbon-based Cathode Research Articles

A compact, membrane-less, easy-to-use soil microbial fuel cell: Generating electricity from household rice washing wastewater

The soil microbial fuel cell (SMFC) is a potential technology for bioelectricity generation. An SMFC can convert chemical energy from organic compounds to electrical energy by utilizing exoelectrogenic bacteria existing in the soil. However, the conventional SMFC configuration is hard to set up and inconvenient to use. In addition, rice is one of the main staple foods worldwide, especially in Asia. Rice washing wastewater (RWW) contains various organic compounds with starch, minerals, and vitamins. In this study, a new design of a compact, portable, membrane-less SMFC is proposed. The SMFC is low-cost, easy-to-use, and can generate bioelectricity from abundant household RWW. The SMFC with double carbon-based anode and cathode electrodes was evaluated in muddy soil (total carbon (TC): 85,200 mg/kg, pH: 4.5, and electrical conductivity (EC): 1.36 dS/m) and sandy soil (TC: 1970 mg/kg, pH: 6.6, and EC: 0.01 dS/m) in an incubator at 30 ± 2 ℃. Household RWW was used as a carbon source to feed bacteria in the soil to power the SMFC. For comparison, a control experiment was also conducted, where only water was added to maintain the soil humidity. 15 mL of RWW or water was added to the SMFCs every 48 h. The result showed that when muddy soil was used, the maximum power density of the SMFC with RWW supplied was 485.2 mW/m2, which was 2.4 times higher than the controlled SMFC (202.9 mW/m2). When sandy soil was used, the SMFC with RWW supplied generated the maximum power density of 112 mW/m2, while that of the controlled SMFC was almost zero. These results imply that the proposed SMFC can operate in different types of soil and effectively generate bioelectricity from RWW.

Nanostructured Carbon-based Cathode Materials for Non-aqueous Li-O2 Batteries

Carbon-based materials have enabled the fabrication of various energy conversion and storage devices with enhanced performances. In this paper, we review in detail different nanostructured carbon-based materials (such as commercial carbon, carbon nanotube/nanofibre, graphene, porous carbon, functionalised carbon, and composite carbon materials with noble metals and metal oxides) as cathodes for non-aqueous Li-O2 batteries. From a materials point of view, the latest trends (mostly since 2012) in the design of catalysts for non-aqueous Li-O2 batteries are discussed. Finally, a summary and outlook for nanostructured carbon-based materials for non-aqueous Li-O2 batteries are presented, including the challenges that lie ahead.

A conductive and ordered macroporous structure design of titanium oxide-based catalytic cathode for lithium–sulfur batteries

The application of lithium–sulfur (Li–S) batteries is hindered by the insulating characteristic of sulfur and slow reaction kinetics of lithium polysulfides. Here, we propose a three-dimensionally ordered macroporous (3DOM) structured conductive polar Ta-doped TiO2 framework with supported Co active site (CoTa@TiO2) to enhance the conversion kinetics of polysulfides. The 3DOM structure serves as an efficient sulfur host for the active sulfur through abundant pores and adsorption site. At the same time, the macropores can buffer the volume expansion of sulfur and enlarged mass transfer. The strong electrostatic attraction between Ti–O bond and polysulfide also promotes the adsorption of polysulfides. Moreover, the doped-Ta improves the conductivity of TiO2 by narrowing the band gap, whereas the supported Co can accelerate the catalytic transformation. Benefited from advanced structural design and synergistic effect of Co and Ta doped TiO2, the Li–S cell with 3DOM CoTa@TiO2 cathode exhibits an impressive areal capacity of 3.4 mAh cm−2 under a high sulfur loading of 5.1 mg cm−2. This work provides an alternative strategy for the development of carbon-based cathode materials for Li–S batteries.

Long-term evaluation of an air-cathode microbial fuel cell with an anion exchange membrane in a 226L wastewater treatment reactor

Although the treatment of municipal wastewater using microbial fuel cells (MFCs) has been extensively studied, scaling the systems up for practical use remains challenging. In this study, a 226 L sewage treatment reactor was equipped with 27 MFC units, and its chemical oxygen demand (COD) removal and electricity production were evaluated. The MFC units were tubular air cores with a diameter of 5 cm and length of 100 cm, which were wrapped with a carbon-based cathode, anion exchange membrane (AEM), and nonwoven graphite fabric. The air-cathode–AEM MFC generated 0.12–0.30 A/m2, 0.072–0.51 W/m3, and 1.7–4.6 Wh/m3 in a chemostat reactor with a COD of 140–36 mg/L and hydraulic retention time (HRT) of 9–42 h throughout a year. The decrease in the COD was represented as the first-order rate constant of 0.038. The rate constant was comparable to that of other air-cathode MFCs with cation exchange membranes, indicating the necessity of a posttreatment to meet the discharge standard. It has been estimated that the MFC operation for 24 h before post-aeration can reduce the energy required to meet the discharge standard by 70%, suggesting the potential applicability of MFC in long HRT-treatments such as oxidation ditch. The resistances of the anode, cathode, and AEM were 15, 7.0, and 0.51 mΩ m2, respectively, and surface dirt rather than deterioration primarily increased the AEM resistance. A current exceeding 0.2 A/m2 significantly increases the anode potential, indicating that the current was limited by low COD. Increasing the anode-specific surface area can improve air–AEM MFCs used for practical applications.

Understanding the role of lithium bonds in doped graphene nanoribbons as cathode hosts for Li‐S batteries: A first‐principles study

Using first-principles calculations, we investigate a family of doped graphene nanoribbons (GNRs) for their suitability as cathode hosts in lithium-sulfur batteries. We probe the role played by the lone pairs of the dopants in confining the lithium polysulfides (LiPS) to understand the mechanism of binding. Our results show that the Li bond between the polysulfides and the doped GNRs is analogous to a hydrogen bond and also dipole-dipole interactions play a key role in anchoring the polysulfides. A critical donor-Li-acceptor angle of 180° is found to be essential for proper adsorption of LiPS, highlighting the importance of the directionality of lone pairs. The charge lost by the sulfur atom of the polysulfide upon adsorption and shape of the lone pair basins and the value of Electron Localization Function (ELF) at the dopant position can provide a quick estimate of the strength of the bond. Significant contractions in the ELF profiles are also observed upon Li2S adsorption, further providing evidence for the hydrogen bond-like nature of the Li bond. Our results corroborate the fact that all acceptors capable of forming hydrogen bonds can be employed as suitable dopants for carbon-based cathode hosts in Li-S batteries.

Targeted Lead and Copper Removal from Aqueous Streams Using Carbon Electrodes in an Electrochemical Filter

Lead contamination in drinking water is a pervasive health problem across the US, brought into the public spotlight by the 2014 water crisis in Flint, Michigan. The Environmental Protection Agency (EPA) established The Lead and Copper Rule in 1991 to limit exposure of these elements and set the action level to 15 ppb; however, there is no safe level of lead consumption.1 Despite corrosion prevention measures taken by public water authorities, lead concentrations in drinking water are routinely elevated nationwide.2 A reliable long-lasting water filter that can specifically target lead and other metals is currently lacking in the marketplace. Metals removal from wastewater is also a major concern for many industries, where water reuse is becoming commonplace, regulations are getting more stringent, and discharge limits must be met. Much of this current work has focused on lead and copper removal from drinking water and industrial wastewater, with a specific focus on commercializing a technology that can provide clean water in a sustainable manner. Applying this technology to other metals of interest has also been demonstrated.Conventional and electrochemical methods for metals removal from water cannot effectively distinguish between many dissolved species and behaves more as a bulk removal process. In order to obtain a purified or concentrated stream of a desired metal, additional separation steps need to be used, making the overall process more expensive and complicated. PowerTech Water has developed carbon electrodes in an electrochemical filter that can target specific metals in a water stream to either remove or recover them, depending on the application. The device uses activated carbon electrodes and a small applied voltage (<2.0 V) to induce Faradaic reactions at both the carbon-based anode and cathode within the cell. By tuning the device configuration and operating parameters, a targeted metal will precipitate out of solution, generally according to its Pourbaix diagram, and be trapped within the porous electrode matrix.Electrochemical water treatment was performed at a constant applied voltage with lead spiked tap water, achieving >90% removal of the target metal, while leaving other species (eg. Na+ and Ca2+) in solution. SEM and EDX analysis of the used anodes and cathodes confirmed the presence of lead species (Figure 1, right panel). To further understand the mechanisms at play, the near electrode pH and voltage distribution were measured. By varying the applied potential, the pH and voltage at the anode and cathode were recorded, along with the concentration of lead at the inlet and outlet. This information, when combined with the Pourbaix diagram, can be used to help identify the lead speciation at each electrode and optimize device performance. Additional experiments were performed with copper spiked tap water, demonstrating the versatility of the electrochemical filter described here.

Primary insights into the effects of organic pollutants and carbon-based cathode materials in a double chambered microbial fuel cell integrated electrocatalytic process

Cathode plays an important role on the oxygen reduction reaction (ORR) reactivity in the microbial fuel cell integrated electrocatalytic process for the effective degradation of organic pollutants. Comparative study of caffeine and phenol as the organic pollutants in the cathodic chamber was investigated in terms of removal efficiency and bioelectricity generation. Results revealed that the highest removal efficiency of phenol (96.89 ± 1.26%) and maximum power density (33.37 ± 4.62 mW m−2) were attained by copper (II) oxide loaded carbon felt (CuO/CF) cathode. Besides, the removal efficiency of phenol was nearly 12-fold higher (24.85 ± 1.36%) using CuO/CF cathode compared with that of caffeine (2.14 ± 0.36%) at the first 24 h. The effect of carbon-based cathode materials on the mineralization of caffeine in the cathodic chamber was evaluated using carbon felt (CF) and carbon plate (CP). Both CuO/CP and bare CP cathodes surpassed CuO/CF and bare CF cathodes in the chemical oxygen demand (COD) removal and bioelectricity generation. Higher crystallinity nature and electrical conductivity (3.57 × 105 Ω−1 m−1) of CP compared with that of amorphous structure and lower electrical conductivity of bare CF (3.33 × 104 Ω−1 m−1) contributed to higher ORR reactivity and efficient transport of electrons for bioelectricity generation. The COD removal efficiency of synthetic wastewater in the anodic chamber and bioelectricity generation of this integrated system were affected by the types of organic pollutants and carbon-based cathode materials in the cathodic chamber.

Advanced oxidation treatment of amaranth dye synchronized with electricity generation using carbon-based cathodes in a sustainable photocatalytic fuel cell integrated electro-fenton system

Cathodes are key components in the photocatalytic fuel cell (PFC) integrated electro-Fenton (EF) system (PFC-EF system) as they play significant role in connecting PFC and EF for the external transfer of electrons. In this study, three ubiquitous carbon-based materials (carbon felt (CF), carbon plate (CP) and carbon cloth (CC) were used as cathodes in the PFC-EF system to explore the efficiency of these materials in Amaranth degradation and electricity generation synchronously. Interestingly, the dye decolourisation efficiency in both PFC and EF decreased in the sequence of CF > CP > CC. The highest concentration of hydrogen peroxide (0.289 mM) was electro-generated on CF in the EF process of the integrated system. CF achieved the highest voltage output of 202.6 mV and maximum power density (Pmax) of 3.560 μW cm-2, which was 2.5-fold and 12.1-fold higher than that of CP and CC, respectively. The photolysis reaction of UV contributed to the higher oxidizing power of PFC integrated photo-electro-Fenton (PEF) system in dye degradation compared with that of the existing PFC-EF system. Enhanced decolourisation efficiencies of 98.97% and 96.46% were respectively achieved in PFC and PEF with Pmax of 4.017 μW cm-2.

Effect of Sodium Penetration on Microscopic Deformation of Carbon-Based Cathode Materials During Aluminum Electrolysis

Effect of Sodium Penetration on Microscopic Deformation of Carbon-Based Cathode Materials During Aluminum Electrolysis

Response Surface Methodology to Investigate the Comparison of Two Carbon-based Air Cathodes for Bio-electrochemical Systems

: Bio-electrochemical technologies can generate renewable electrical bioenergy from oxidation of organic materials through the catalytic reactions of the microorganisms while treating the wastewater. In this study, the use of carbon aerogel as a novel catalyst with high porosity(the total pore volume of 1.84 cm3g-1) and high surface area (491.7 m2/g) for improving the oxygen reduction reaction (ORR) performance was compared to that of the conventional activated carbon, employed as an air cathode catalyst in bio-electrochemical systems, with the indigenous bacterial consortium. The electrochemical studies revealed the higher power efficiency in the use of carbon aerogel (with the maximum power density and current density of a 675 mWm-2 and 33.1 mAm-2, respectively), as compared to the activated carbon (with the maximum power density and current density of 668.98 mWm-2 and 23.2 mAm-2, respectively). The performance of the two materials and optimum conditions for electricity production were examined using the Response Surface Method (RSM) as an optimal design method. Statistical analysis confirmed that the carbon aerogel performed better than the activated carbon in power production and facilitated cathodic redox reactions. Comparison of two catalysts showed that the redox reactions occurred in the presence of carbon aerogel more facilitated and in a wider range, produced 1.2 times more current (the maximum 2.1 mA and 1.69 mA current). Carbon aerogel, with a suitable load absorbance and resistance to oxidation at urban wastewater pH can be, therefore, coated on electrodes to facilitate the oxidation-reduction reactions and electricity transmission.

Boosting zinc-ion storage capability by engineering hierarchically porous nitrogen-doped carbon nanocage framework

In virtue of combining superb power of supercapacitors and high energy of batteries, zinc-ion hybrid supercapacitors become a competitive candidate in current energy storage systems. However, the cell chemistry related to carbon cathode still suffers from the obstacles of reaction kinetics and charge storage efficiency. Herein, a three-dimensional framework of N-doped carbon nanocages is constructed through pyrolyzing and activating polypyrrole on the platform of ZIF-8, synchronously achieving hierarchical porosity and high N-doping content. Thanks to the comprehensive modulation of the morphology, pore structure, and surface chemistry, the obtained carbon shows the significant enhancement in active site exposure and diffusion kinetics. Therefore, the zinc-ion hybrid supercapacitor using this carbon cathode achieves the remarkably improved Zn-ion storage capability (124 mAh g−1 at 0.25 A g−1 with a 65.9% capacity retention at 20 A g−1, and nearly no capacity decay after 10000 cycles at 10 A g−1). Moreover, this device exhibits superior energy/power densities of 107.3 Wh kg−1/16647.7 W kg−1, together with a low self-discharge rate of 3 mV h−1. Our work presents a good design strategy to develop advanced carbon-based cathodes to accelerate the development of Zn-based devices.

Porous Carbon Architecture Assembled by Cross-Linked Carbon Leaves with Implanted Atomic Cobalt for High-Performance Li–S Batteries

HighlightsSiO2-mediated ZIF-L is developed to prepare Co–N4@2D/3D carbon.Co–N4@2D/3D integrates the advantages of 0D Co single atom and 2D/3D carbon support.Co–N4@2D/3D carbon-based sulfur cathode enables a high reversible specific capacity and low capacity fading rate.

Beyond the farm: Making edible protein from CO2 via hybrid bioinorganic electrosynthesis

Beyond the farm: Making edible protein from CO2 via hybrid bioinorganic electrosynthesis

Mechanism and Performance of a CO2-Driven Li-O2 Battery Containing LiBr

The environmental friendly aprotic lithium–oxygen (Li–O2) battery with high theoretical energy density has received great attention in the past years. A necessary shift to a direct exploitation of atmospheric air to assure the practicality of these devices has, however, demonstrated that the presence of CO2 and moisture fundamentally alters the O2 electrochemistry of the cell. The uncovered effect of CO2 in Li–O2 cells in a tetraglyme-electrolyte under a wide O2:CO2 mixture range revealed that with up to 30% CO2, the latter acts as an O2 − scavenger during discharge steps, leading to the formation of representative CO4 −/C2O6 2−-based species correlated with enhanced full capacity and cell cyclability. The CO2-driven Li–O2 device suffers, however, from unpractical recharge potentials at ~4.5 V required for the decomposition of Li2CO3. In this work, we investigate the performance of these devices in cells containing LiBr acting as a redox mediator. The electrochemically-generated Br3 –/Br2 redox couple offers a promising pathway to facilitate the decomposition of Li2CO3. We show that hindered overcharges (~0.5 V) are not only a function of the introduced LiBr concentration, but also depend on the crystallinity and morphology of the insulating Li2CO3 discharge product. Coupled electrochemical and spectroscopic analyses shed light on the redox shuttling steps at progressive states-of-recharge, revealing the presence of Br2···Br3 − loosely-bound anionic complexes in the electrolyte. As opposed to discrete polar Br2 irreversibly precipitated on the carbon-based cathode surface, the facile diffusion of the soluble Br2···Br3 − complex pinpoints these species as operating redox mediators. These findings offer insight toward the rational design of efficient mobile mediators beyond an overcharge decrease in the CO2-driven Li–O2 device.

Surface Modification Effect and Electrochemical Performance of LiOH-High Surface Activated Carbon as a Cathode Material in EDLC.

This study aimed to improve the performance of the activated carbon-based cathode by increasing the Li content and to analyze the effect of the combination of carbon and oxidizing agent. The crystal structure and chemical structure phase of Li-high surface area activated carbon material (Li-HSAC) was analyzed by X-ray diffraction (XRD) and Raman spectroscopy, the surface state and quantitative element by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and the surface properties with pore-size distribution by Brunauer–Emmett–Teller (BET), Barrett–Joyner–Halenda (BJH) and t-plot methods. The specific surface area of the Li-YP80F is 1063.2 m2/g, micropore volume value is 0.511 cm3/g and mesopore volume is 0.143 cm3/g, and these all values are higher than other LiOH-treated carbon. The surface functional group was analyzed by a Boehm titration, and the higher number of acidic groups compared to the target facilitated the improved electrolyte permeability, reduced the interface resistance and increased the electrochemical properties of the cathode. The oxidizing agent of LiOH treated high surface area of activated carbon was used for the cathode material for EDLC (electric double layer capacitor) to determine its electrochemical properties and the as-prepared electrode retained excellent performance after 10 cycles and 100 cycles. The anodic and cathodic peak current value and peak segregation of Li-YP80F were better than those of the other two samples, due to the micropore-size and physical properties of the sample. The oxidation peak current value appeared at 0.0055 mA/cm2 current density and the reduction peak value at –0.0014 mA/cm2, when the Li-YP80F sample used to the Cu-foil surface. The redox peaks appeared at 0.0025 mA/cm2 and –0.0009 mA/cm2, in the case of using a Nickel foil, after 10 cycling test. The electrochemical stability of cathode materials was tested by 100 recycling tests. After 100 recycling tests, peak current drop decreased the peak profile became stable. The LiOH-treated high surface area of activated carbon had synergistically upgraded electrochemical activity and superior cycling stability that were demonstrated in EDLC.

A review of carbon-based cathode materials for zinc-ion capacitors

A review of carbon-based cathode materials for zinc-ion capacitors

Removal of organic compounds from shale gas fracturing flowback water by an integrated electrocoagulation and electro-peroxone process

This study investigated the removal of organic compounds from shale gas fracturing flowback water (FFW) by an integrated electro-coagulation and electro-peroxone (EC-EP) process in a divided electrochemical reactor. During the EC-EP process, electricity was efficiently utilized to produce both aluminum ion (Al3+) from electrochemical oxidation of an aluminum anode in the anodic compartment and hydrogen peroxide (H2O2) from oxygen reduction at a carbon-based cathode in the cathodic compartment. The in-situ generated H2O2 then reacted with ozone (O3) sparged in the cathodic compartment to produce hydroxyl radicals (•OH) for pollutant oxidation. The results showed that by sequentially treating the selected FFW by the EC and EP process in the anodic and cathodic compartment for 30 min, respectively, the EC-EP process effectively removed ~95% of total organic carbon (TOC) from the FFW, meeting the wastewater discharge standard for TOC (≤30 mg/L) with a low specific energy consumption of 0.11–0.21 kWh/g TOC removed. In contrast, individual EC and EP process, as well as the previously investigated ECP process that combined the EC and EP process in an undivided reactor, removed only ~76%, 32%, and 80% TOC from the FFW under similar reaction conditions, and thus could not meet the wastewater discharge standard. These results demonstrate that the EC-EP process successfully integrates the merit of the EC and EP process and may thus provide a cost-effective way to remove organic compounds for FFW disposal and reuses.

Carbon-based cathodes degradation during electro-Fenton treatment at pilot scale: Changes in H2O2 electrogeneration

Autopsy of carbon-PTFE cathodes was performed by addressing their degradation in a commercial plate-and-frame cell equipped with a Nb-BDD anode. Cell is arranged within an electrochemical pilot plant designed for treating wastewaters by electrochemical Fenton-like processes, thus an efficient electrocatalytic production of H2O2 is necessary to guarantee Fenton’s reaction. Significant decrease in H2O2 electrogeneration occurred during pilot plant operation, hindering the efficient performance of Fenton-like processes. Two cathodes were studied, first was operated at pH 3 and second at neutral pH by using EDDS as complexing agent to maintain iron in solution. Electrogenerated H2O2 decreased from 43 mg L−1 to 16 mg L−1 in the first cathode after 50 h of operation and from 49 mg L−1 to 24 mg L−1 in the second one after 26 h of operation. Both were cleaned with 30% (v/v) solution of HCl/water for 24 h and H2O2 production was recovered only in the second cathode (able to generate 39 mg L−1). Autopsy of the cathodes was tackled by scanning electron microscopy (SEM) and X-ray energy dispersive (EDX), evidencing a strong degradation of first cathode surface and iron oxide inlays in second one due to the decomposition of Fe3+:EDDS and consequent iron precipitation at neutral pH.

A review of carbon-based cathode materials for zinc-ion capacitors

Zinc-ion capacitors are high-performance hybrid capacitors that have great advantages because of the abundance of zinc resources and their high theoretical capacitance. As a result they have become a hot research topic in the field of energy storage devices. Carbon-based materials are usually used as the cathode materials for these capacitors because of the wide range of available materials, and their easily tuned surface properties and simple fabrication. This review summarizes recent research progress on carbon cathode materials for flexible/non-flexible zinc ion capacitors, and gives a concise description of their novel structures and outstanding performance. It then discusses research on the energy storage mechanisms in the cathode materials and suggests directions for the development of carbon cathodes for zinc-ion capacitors.

Effect of surface characteristics of carbon host on electrochemical performance of nonaqueous Li–O2 batteries

Carbon-based air cathodes are considered the ideal choice for Li–O2 batteries. However, the parasitic reaction on the carbon surface remains a critical hurdle to progress toward practical Li–O2 batteries. To address this issue, an in-depth understanding of the effect of surface chemistry is needed as it is a key factor determining the electrochemical performance of Li–O2 batteries. In this study, to elucidate the relationship between the surface characteristics of carbon and the electrochemical performance of a Li–O2 battery, we prepared a series of porous carbon nanoweb electrodes with systematically controlled surface properties. We then closely investigated the effect of the surface chemistry of carbon on the electrochemical performance of the Li–O2 battery. The key factors greatly contributing to the performance were determined to be the degree of graphitization and the density of oxygen functional groups on the carbon surface. These factors have a strong effect on the initial reaction route for Li2O2 formation, naturally resulting in large differences in the electrochemical properties such as the capacity, cyclability, efficiency, and Li2O2 yield. We define the relationship between the surface properties and key performance factors, and suggest the ideal conditions for a carbon electrode for Li–O2 batteries. Our demonstration will help guide the future design of ideal carbon-based air cathodes for practical Li–O2 batteries.