Bare Carbon Paper Research Articles

Enhancing reaction interface with modified microporous layers for high-efficiency hydrogen production in PEM water electrolysis

Improving the reaction interface is imperative for increasing catalyst utilization and enhancing overall cell performance in proton exchange membrane electrolyzer cells (PEMECs). Herein, a thin Nafion-carbon-mixed microporous layer coated carbon paper (Nafion-C MPL/CP) is first developed as an efficient cathode liquid/gas diffusion layer for PEMECs. With the Nafion-C MPL/CP, low cell voltages of 1.64, 1.74 and 1.84 V are delivered, which are 50, 80 and 140 mV lower than those of the conventional bare carbon paper at 2, 4 and 6 A/cm2, respectively, achieving about 3-fold higher catalyst utilization. Meanwhile, superior performance is also demonstrated compared to the commercial PTFE-C MPL/CP. The remarkable performance of the Nafion-C MPL/CP should be attributed to the enhanced reaction interface, which not only provides rich active sites with abundant electron and proton transport pathways for the electrochemical reaction but also reduces the interfacial contact resistance and mass transport losses. Moreover, excellent stability of the Nafion-C MPL/CP is demonstrated at a current density of 1.8 A/cm2 with no performance degradation during over 100-h operation. Due to the enhanced reaction interface with significantly improved catalyst utilization, the developed Nafion-C MPL/CP shows great potential to reduce the hydrogen production cost and accelerate PEMEC commercialization.

Turbostratic Carbon Nano Onion Electrode for High Power Density Vanadium Redox Flow Battery

The redox flow battery (RFB) is one of the most promising technologies for stationary energy storage. It consists of a voltaic cell whose electrolytes are stored in tanks outside the system. Whilst the chemistries of the anodic and cathodic electrolytes define the energy density of a RFB system, its power density is determined primarily by its electrodes. These are typically porous carbon media on the surface of which the redox reactions occur. They are a critical component since they require a detailed engineering of electrocatalytically active surface area and mass transport. Still today, they remain the main cause of RFB low power density. In this work, we are showing a novel deposition method to improve the performance of commercially available carbon paper already used in RFB.The gain is thanks to the deposition of turbostratic carbon nano-onion (TCNO) nanoparticles on the carbon fibers of the paper. This process is performed with a proprietary technology called NanoJeD: a CVD in supersonic flow, which promises easy industrial scalability and a fine tunability of the nanoparticle properties. Moreover, with this system is possible to deposit over any substrate.NanoJeD consists in two chambers separated by a high aspect ratio slit. A precursor gas is injected through a porous plug from the top and a vacuum system is connected from the bottom. The slit allows the establishment of a high-pressure ratio between the two chambers and hence the formation of a supersonic jet. The precursor gas, a mixture of Argon (98.4%) and Acetylene (1.6%) flows between two electrodes where a radio frequency (RF) signal is fed (13.56 MHz). The RF ignites a non-thermal plasma in which the precursor molecules are ionized and dissociated into radicals, which polymerize forming hydrogenated carbon clusters and nanoparticles (NPs) of different sizes. Once formed, NPs are dragged through the slit by the gas stream and finally impact on the substrate. Therefore, it is possible to achieve a high throughput (500 mg h-1) and to deposit on a large area of 100 cm2 while precisely controlling the properties of the film. The resulting film has hundreds of squared meters per gram of surface area. For TCNO formation, the NP film is further annealed in vacuum at 1000°C for 2 hours. Using in situ transmission electron microscopy (TEM) and energy electron loss spectroscopy (EELS), we were able to visualize the progression of graphitization and changes in structural properties during annealing. The graphitization process starts in the outer layer and proceeds into the interior of the particle. The geometrical constrains of the NP (average diameter of 20nm) and shrinkage of the NP, allow the formation of curved, turbostratic, defective graphitic sheets. UV photoelectron spectroscopy (UPS) and Raman spectroscopy performed ex-situ allow the analysis of valence bands and structural defects. The high presence of defects and general disorder structure are accompanied with a remarkable increase in catalytic activity. Moreover, the annealing process leads to the sintering of the nanoparticles and the formation of an interface between the carbon fibre and the nanoparticles, as demonstrated by the increased thermal stability tested by. Both phenomena improve the adhesion between nanoparticles and with the surface, making the electrode suitable to be adopted in fluxed systems.The TCNO deposited on a carbon paper was tested as electrode in a Vanadium RFB. The kinetic activity and electrochemical properties were tested via in-situ Raman and in a three-electrode cell set-up. The results reveal an increased kinetic activity with respect to the untreated paper. Using in situ Raman we were able to show differences in redox mechanism between TCNO and bare carbon paper. A chronoamperometry test was used to obtain the transfer coefficient from a Tafel plot. These studies allow the correlation of the catalytic activity with the defectiveness of the TCNO nanoparticle. Vanadium RFB full cell measurements of the TCNO electrode show a drastic increase in performance, reaching an energy efficiency of 70.8% and 86.2% at current densities of 600 mA cm-2 and 200 mA cm-2, respectively. The electrolyte utilisation for these current densities is 59% for the former and 80% for the latter. To investigate the chemical and mechanical stability a stability test was performed. Results showed a low degradation rate of 0.004% EE per cycle. Moreover, TCNO can be used for other electrochemical applications only by adjusting the deposition and annealing parameters.

Exploring Conductive Polymer Coatings to Target Reaction Selectivity in Aqueous All-Iron Redox Flow Batteries

An energy grid that relies on wind and solar farms requires the installation of large-scale energy storage systems to balance their fluctuating output. Especially for developing countries, wide adoption of renewables is coupled to progress in sustainable and cost-effective storage technologies.1 From this perspective, aqueous all-iron redox flow batteries (AIRFBs) stand out as a promising technology, owing to the earth-abundance and low-cost of iron, along with its environmental and operational safety. In this battery, iron is utilized in its three oxidation states (Fe0, Fe2+ and Fe3+) and the negative electrode leverages the iron plating/stripping reactions to sustain charge and discharge. However, the standard potential of iron plating is 0.44 V below the hydrogen evolution reaction (HER), which causes faradaic losses during the charging stage and increases the pH of the solution.2 The catalytic activity of iron towards hydrogen evolution and the precipitation of iron hydroxide at pH above 3.5 further complicates the operation of AIRFBs. Thus, the reaction selectivity of the negative electrode should be targeted to improve the operational time and efficiency. So far, research has focused on electrolyte engineering to hinder adsorption of hydrogen on surfaces or excluding water from the solvent shell of iron.2,3 Alternatively, interfacial engineering of electrode surfaces can be a promising strategy to tune the reaction selectivity, given that hydrogen adsorption and iron nucleation are interfacial phenomena. The challenge here is to prevent a new interface from being created by the plated iron as that would render the modified interface obsolete. We hypothesize that polymeric layers where iron deposition can take place within or underneath the polymer (akin to a solid electrolyte interphase of a Li-ion battery anode) would preserve the HER-inhibiting characteristics of the surface.Here, we propose conductive polymer interfaces to target reaction selectivity during the iron plating reaction. Conductive polymers have been used to engineer HER-inhibiting interfaces and as corrosion protection layers for metals.4,5 Furthermore, they can be conformally coated on porous electrodes, enabling their use in flow reactors.6 We selected two conductive polymer systems: poly(pyrrole) (PPy) owing to its iron-coordinating nitrogen moieties and poly(3,4-ethylenedioxythiophene) (PEDOT) owing to its high conductivity and stability.7 Furthermore, we employed three counterions of different size, chlorine (Cl-), p-toluenesulfonate (pTS-) and poly(styrenesulfonate) (PSS-), to direct the morphology of the coating, resulting in six different polymer systems. On glassy carbon electrodes, all polymers significantly hinder HER at potentials as low as -1.5 V (vs Ag/AgCl) where heavy bubble formation is observed on bare electrodes (Figure 1). To assess the selectivity of the coatings on carbon paper substrates, we are developing an electrochemical protocol with successive plating/stripping cycles that is representative of battery operation. Preliminary results show that all polymer systems hinder the HER, but also the Fe-plating reaction, resulting in lower plating currents than the bare carbon paper electrodes. To validate the methodology, we compare the electrochemically obtained reaction selectivity values with the ones from gravimetric analysis. The ideal polymeric interfaces should inhibit the HER without largely impacting the Fe-plating kinetics, which motivates research into the relationship between the coating thickness, conductivity, and the faradaic efficiency. To understand the plating morphology on polymeric coatings, we investigate the spatial distribution of iron on the surface and the cross-section of plated electrodes using microscopic methods. Hydrogen evolution and limited durability due to complex plating reactions hamper the broad implementation of all-iron redox flow batteries and we hope to tackle these challenges through interfacial electrode engineering. References Rahman et al., in Renewable Energy and Sustainability, Elsevier, 2022, pp. 347–376. Hawthorne et al., J. Electrochem. Soc. 2014, 162, A108.Liu et al., ACS Cent. Sci. 2022, 8, 729.Tian et al., J. Electrochem. Soc. 2013, 161, E23. Deshpande et al., J Coat Technol Res 2014, 11, 473. Boz et al., Adv Materials Inter 2023, 2202497. Mao et al., Energy Environ. Sci. 2011, 4, 3442. Figure 1

Lithiophilic Nanowire Architectures as Hosts for Lithium Metal Anodes

Lithium (Li) metal is considered the ‘holy grail’ of battery anodes and has attracted enormous interest due to its low density (0.59 g cm-3), high theoretical capacity (3860 mAh g-1) and lowest electrochemical potential (-3.07 V vs. standard hydrogen electrode - SHE) [1-2]. However, several issues during its cycling in a Li-metal battery (LMB) have hindered its commercialization. Some notable problems include the formation of an unstable solid electrolyte interphase (SEI), excessive dendrite growth and subsequent short-circuiting during the Li stripping/plating process [3-4].In our poster presentation, we will detail the design of a hierarchical nanowire (NW) – Carbon paper (CP) host for dendrite-free and stable cycling in LMBs. These NWs were grown on high surface area carbon paper substrate via a modified Vapour-Liquid-Solid (VLS) approach. The lithiophilic NWs enabled quick Li infusion (< 10 sec) in the NW-CP substrate whereas no Li infusion was possible in lithiophobic bare CP substrate (without the presence of NWs). Additionally, the NW morphology helped in reducing the localized current density on the surface of the NW-CP host, thereby promoting uniform Li deposition during plating/stripping process. With careful design of the NW-CP host, symmetric cell performance with high current density (3 mA cm-2) and areal capacity (3 mAh cm-2) was achieved for up to 500 h while a typical Li metal anode failed within 200 h. High loading NMC811 and high specific capacity Sulfur (S) cathodes demonstrated superior performance using NW-CP host as compared to pristine Li anodes.In addition, we will also present some new concepts of NW decorated lithiophilic interlayers, which can be integrated with pristine Li metal anodes for uniform Li deposition. These lithiophilic interlayers can promote ‘bottom-up’ Li infilling between the Li-interlayer interface such that dendrite formation near the separator and eventual short-circuit is avoided. Detailed electrochemical as well as density functional theory (DFT) analysis shedding light on the improved lithiophilic properties of NW use in stabilizing Li metal anodes will also be presented. Overall, our work is aimed to develop high energy density (ED) Li metal anodes to meet the rising ED demands of electric vehicle (EV) industry.

Ultrasonic Spray Coating to Optimize Performance of Bio-Electrochemical Systems.

This work investigates the optimization of carbon-based electrodes employed in bio-electrochemical systems (BES) through the deposition of nanostructured layers of poly(3,4-ethylene-dioxy-thiophene) poly(styrene-sulfonate) (PEDOT:PSS) on commercial carbon paper electrodes via ultrasonic spray coating (USC). This innovative application of USC demonstrated that uniform and controlled depositions of PEDOT:PSS can be successfully performed on carbon-based electrodes. To this end, the morphology and spatial uniformity of depositions were verified via scanning electron microscopy and Raman spectroscopy. Electrochemical characterizations of fabricated electrodes demonstrated a more than two-fold increase in the electrochemical active surface area with respect to bare carbon paper. A lab-scale experiment on BES was performed, selecting microbial fuel cells (MFCs) as the reference devices. Devices featuring USC-deposited PEDOT:PSS electrodes showed a three-fold-higher energy recovery with respect to control cells, reaching a maximum value of (13 ± 2) J·m-3. Furthermore, the amount of PEDOT:PSS required to optimize MFCs' performance is in line with values reported in the literature for other deposition methods. In conclusion, this work demonstrates that USC is a promising technique for application in BES.

Electrocatalytic Nitrate Reduction to Ammonia at Atomically Dispersed Titanium Sites on Carbon Nanoflowers

Active nitrogen species are widely acknowledged as pollutants that are both harmful to the environment as well as human health. Emissions from wastewater and agricultural applications contain nitrogen in many forms, but in soils and waterways nitrate (NO3 -) predominates due to the presence of nitrifying bacteria. In comparison to more reduced forms of nitrogen such as total ammonia (NH3/NH4 +), nitrate is not only a less versatile species from a chemical manufacturing and energy standpoint; it is also more difficult to selectively separate from wastewater streams. For instance, we have conducted considerable work on electrochemical ammonia stripping, achieving high selectivities and even enabling concentration of ammonia in the form of strong ammonium salt solutions.1 Moreover, it is estimated that recovery of active nitrogen species from municipal and agricultural wastewaters could offset the need for ~30% of Haber-Bosch ammonia synthesis. From this perspective, it is desirable to develop catalysts that are active and selective for the conversion of nitrate to ammonia. Titanium metal has been demonstrated as a relatively active and selective catalyst for nitrate reduction to ammonia in acid;2 however, similarly active and selective catalysts under neutral-to-alkaline conditions are a subject of active research.3–6 Here we report on the performance of atomically dispersed titanium sites on carbon nanoflowers7 for the reduction of nitrate to ammonia under alkaline conditions. The dispersity of these catalysts was supported by XAS (little/negligible Ti-Ti scattering, putative Ti-N and Ti-N-C scattering), STEM (visual confirmation of atoms), and XRD (no crystalline Ti phases observed). We contrast the performance of these atomically dispersed catalysts with that of bulk titanium foil, which shows comparably low activity and selectivity for nitrate reduction at similar pHs and potentials. In addition, we compare the atomically dispersed titanium catalysts with titanium nanoparticles, as a first-order check for catalyst aggregation under reductive reaction conditions. Moreover, the performances of all of these catalysts are compared with the baseline/controls of bare carbon paper, as well as carbon nanoflowers supported on carbon paper without titanium dopant. Additional control experiments include tests conducted in the absence of nitrate. These lines of evidence, together with the relatively high rate of ammonia production (>0.01 mmol / cmgeo 2 / h, >10 mmol / mg Ti / h), support the notion that atomically dispersed titanium is uniquely active and selective for NO3RR under alkaline conditions.Further, for the above catalysts at pH ~13, we show the impacts of potential on the product distribution, including nitrogen mass balance and Faradaic efficiency. As a best practice, we demonstrate consistent closure of both metrics. Potential was varied between -0.4 V and -0.85 V vs. RHE. Partial current toward NO3RR increases with increasing overpotential, as another sanity check supporting the findings. Notably, in addition to observing ammonia and nitrite as products of NO3RR, we also checked for other stable intermediates (in addition to N2) along the 8-electron reaction pathway – and as a result, we are able to report small amounts (FE ~5-10%) of hydroxylamine (NH2OH) product.In the specific case of atomically dispersed titanium on carbon nanoflowers, we also report on certain observed electrolyte effects, such as the incorporation of perchlorate vs. sulfate as a supporting electrolyte. We demonstrate the role of supporting salt both in modifying selectivity – e.g. sulfate suppressing HER, possibly via site-blocking – as well as in altering the carbon support itself. These observations contribute to a growing body of work that will enable the engineering of these catalysts for high-rate reduction of nitrate to ammonia, aiding both wastewater remediation and the decarbonization of ammonia synthesis.

Enhancement of supercapacitor activity of MoS2 electrocatalyst via incorporation of copper interlayer

In this work, we are reporting the synthesis of MoS 2 nanoparticles prepared using hydrothermal method at 180 °C. We have characterized the phase, morphology, composition, using X-ray diffraction, scanning electron microscopy techniques. We have fabricated two electrodes for electrochemical testing by loading MoS 2 nanoparticles onto (i) bare carbon paper, and (ii) Cu electrodeposited carbon paper. We found that copper interlayer addition increases the electronic conductivity which, in turns, increases the surface energy of the electrocatalyst, leading to an increase in cycle life. Further, the copper interlayer increases the number of active sites via increase of Mo 3+ at the catalyst surface.

Carbon Paper Modified with Functionalized Poly(diallyldimethylammonium chloride) Graphene and Gold Phytonanoparticles as a Promising Sensing Material: Characterization and Electroanalysis of Ponceau 4R in Food Samples

This paper presents a novel eco-friendly sensing material based on carbon paper (CP) volumetrically modified with a composite nanomodifier that includes functionalized poly(diallyldimethylammonium chloride) graphene (PDDA-G) and phytosynthesized gold nanoparticles (phyto-AuNPs). The functionalization of graphene was justified by Fourier-transform infrared spectroscopy. The phyto-AuNPs (d = 6 nm) were prepared by "green" synthesis with the use of strawberry leaf extract. The sensing material was characterized using scanning electron microscopy, electrochemical impedance spectroscopy, and voltammetry. The research results indicated a more than double increase in the electroactive surface area; a decrease in the resistance of electron transfer on nanocomposite-modified CP, compared to bare CP. The phyto-AuNPs/PDDA-G/CP was used for the electrosensing of the synthetic dye Ponceau 4R. The oxidation signal of colorant enhanced 4-fold on phyto-AuNPs/PDDA-G/CP in comparison to CP. The effect of the quantity of nanomodifier, solution pH, potential scan rate, accumulation parameters, and differential pulse parameters on the peak current of Ponceau 4R was studied. Under optimal conditions, excellent sensory characteristics were established: LOD 0.6 nM and LR 0.001-2 μM for Ponceau 4R. High selectivity and sensitivity enable the use of the sensor for analyzing the content of Ponceau 4R in food products (soft drinks, candies, and popsicles) without additional sample preparation.

Development of a High-Performance and Robust PANI:PSS/C Electrode for an Electroosmotic Pump

A high-performance and durable electroosmotic (EO) pump is developed by using electropolymerized PANI:PSS/C electrodes. PANI:PSS was electrochemically synthesized on the carbon fiber paper using cyclic voltammetry and characterized by a variety of physicochemical methods including field emission scanning electron microscopy (FESEM), electron probe microanalyzer (EPMA), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). There was a linear relationship with a regression coefficient R2 ≥ 0.97 between the applied potential and the peak current (Ipeak), maximum flow rate (Qmax), maximum pressure (Pmax), respectively. The EO pump built with PANI:PSS/C electrodes, with an active area of 1.0 cm2, generated the maximum stall pressure of 122 kPa and the maximum flow rate of 203 ul min−1 at 4 V by using deionized (DI) water as a working fluid. The EO pumps assembled with PANI:PSS/C electrodes showed much better overall performances than those made with the bare carbon paper and exhibited good long-term stability without substantial decay for 5 days of continuous operation even at a high potential of 4 V.

A green and easy-to-assemble electrochemical biosensor based on thylakoid membranes for photosynthetic herbicides detection

In this study, we report on an easy-to-assemble amperometric electrochemical biosensor incorporating thylakoid membranes for the detection of photosynthetic herbicides. These molecules interfere with the light-induced photosynthetic electron transport occurring at the level of the photosystems within the thylakoid membranes, thus reducing the current of the associated bioelectrode. Thylakoid membranes isolated from pea plants were adsorbed directly on a bare carbon paper working electrode and placed in the measurement cell in the absence of any electrochemical mediator, obtaining a fully environmental-friendly biodevice capable of photocurrent densities up to 14 μA/cm2. Three photosynthetic herbicides inhibiting Photosystem II and belonging to different chemical classes, namely diuron, terbuthylazine and metribuzin, were detected by measuring the electrode photocurrent, which decreased reproducibly in a concentration-dependent manner in a range between 10−7 – 5 × 10−5 M of each herbicide. The limit of detection for the three herbicides was between 4–6 × 10−7 M. Storage stability tests revealed for the biosensor a half-life longer than 15 days at 4 °C and full stability up to 4 months at −80 °C. This study provides a simple, environmental-friendly and cost-effective procedure for the fabrication of a mediatorless carbon paper-based electrochemical biosensor characterized by high photocurrents, long storage stability, reproducible detections and good sensitivity.

Living Bacteria Directly Embedded into Electrospun Nanofibers: Design of New Anode for Bio-Electrochemical Systems

The aim of this work is the optimization of electrospun polymeric nanofibers as an ideal reservoir of mixed electroactive consortia suitable to be used as anodes in Single Chamber Microbial Fuel Cells (SCMFCs). To reach this goal the microorganisms are directly embedded into properly designed nanofibers during the electrospinning process, obtaining so called nanofiber-based bio-composite (bio-NFs). This research approach allowed for the designing of an advanced nanostructured scaffold, able to block and store the living microorganisms inside the nanofibers and release them only after exposure to water-based solutions and electrolytes. To reach this goal, a water-based polymeric solution, containing 5 wt% of polyethylene oxide (PEO) and 10 wt% of environmental microorganisms, is used as the initial polymeric solution for the electrospinning process. PEO is selected as the water-soluble polymer to ensure the formation of nanofiber mats offering features of biocompatibility for bacteria proliferation, environment-friendliness and, high ionic conductivity. In the present work, bio-NFs, based on living microorganisms directly encapsulated into the PEO nanofiber mats, were analyzed and compared to PEO-NFs made of PEO only. Scanning electron microscopy allowed researchers to confirm the rise of a typical morphology for bio-NFs, evidencing the microorganisms’ distribution inside them, as confirmed by fluorescence optical microscopy. Moreover, the latter technique, combined with optical density measurements, allowed for demonstrating that after electrospinning, the processed microorganisms preserved their proliferation capability, and their metabolic activity after exposure to the water-based electrolyte. To demonstrate that the energy-production functionality of exo-electrogenic microorganisms was preserved after the electrospinning process, the novel designed nanomaterials, were directly deposited onto carbon paper (CP), and were applied as anode electrodes in Single Chamber Microbial Fuel Cells (SCMFCs). It was possible to appreciate that the maximum power density reached by bio-NFs, which resulted in being double of the ones achieved with PEO-NFs and bare CP. SCMFCs with bio-NFs applied as anodic electrodes reached a current density value, close to (250 ± 5.2) mA m−2, which resulted in being stable over time and was comparable with the one obtained with carbon-based electrode, thus confirming the good performance of the whole device.

Promoting the anode performance of microbial fuel cells with nano-molybdenum disulfide/carbon nanotubes composite catalyst.

The design and manufacture of advanced anode materials with superior quality are significant for assembling high-performance microbial fuel cells (MFCs). The present study aims to investigate the synergistic effect of MoS2/CNTs nanocomposite as a novel anode-modifying material of MFCs. XRD, XPS, SEM, TEM and electrochemical analyses were performed to confirm the nanocomposite, to understand the morphology and to study the electrochemical properties of the modified electrodes. The performance of the MoS2/CNTs/carbon paper (CP)-MFCs was investigated and compared with that of MoS2/CP-MFCs, CNTs/CP-MFCs and CP-MFCs. The densest biofilm was formed on MoS2/CNTs-modified anode compared to MoS2/CP, CNTs/CP and CP anode, and MFCs with MoS2/CNTs-modified anodes achieved the maximum power density of 645 ± 32mWm-2, which is three times greater than MFCs with bare carbon paper anodes (213 ± 10mWm-2). These results demonstrate that the synthesized MoS2/CNTs nanocomposite could be exploited as an efficient anode catalyst for improving the performance of MFCs.

Effects of Oxygen Cathode Substrates with Various Carbon Catalysts on the Discharge Capacity of Lithium-Oxygen Battery

Lithium-oxygen batteries have been considered strong candidates to supersede current rechargeable batteries especially lithium-ion batteries. Despite having tremendously high theoretical energy density, the practically achievable energy density is far from commercial application till date. The oxygen electrode is one of the major bottlenecks in maximizing the battery capacity. It is comprised of a porous structure (mainly carbon) with high surface area and sufficient reaction sites. High porosity facilitates lithium ion and oxygen mass transfer and results in high storage capacity for the insoluble discharge product during discharging. The cathode electrode is fabricated by coating a catalyst layer on a porous carbon substrate. The substrate, which contacts with oxygen channels, plays a vital role in mass transfer of oxygen from outside to the reaction sites. Therefore, it is important to select a substrate that does not clog with deposition of Li2O2 particles immediately after discharging begins and allows oxygen to reach the catalyst side for longer period of time.This study investigates the effects of oxygen electrode substrates with various coating materials on the discharge capacity of lithium-oxygen battery. For this purpose, we have compared the discharge capacity of plain carbon cloth, plain carbon paper and carbon cloth or carbon paper coated with carbon catalysts including Vulcan XC, Super P and Graphene Oxide. 1.5mg/cm2 (+/-0.3mg/ cm2) is used as catalyst loading. The electrolyte used in this study is 1M LiTFSI in TEGDME. PTFE (30wt%) is used as a binder. All experiments are conducted at room temperature with pure oxygen supply.With carbon cloth as a substrate, the discharge capacities obtained were 3 to 6 times higher (depending on the carbon catalysts coated) than the capacities obtained with carbon paper. The bare carbon cloth, Vulcan XC, Super P and Graphene oxide with carbon cloth as a substrate have discharge capacities of 0.11 mAh/mg, 13 mAh/mg, 6.8 mAh/mg, 1.5 mAh/mg respectively. On the other hand, the discharge capacities achieved with bare carbon paper, Vulcan XC, Super P and graphene oxide with carbon paper as substrate were 0.02 mAh/mg, 2.4 mAh/mg, 2.7 mAh/mg, 0.28 mAh/mg respectively. The results clearly indicate that the cathode with carbon cloth as a substrate yields significantly higher discharge capacity with all the coating materials as compared with the carbon paper. The different performances of two substrates can be attributed to their structure and pore size distribution. Carbon cloth is composed of flexible woven threads with longer lengths ( ̴ 30µm) and broader pore size distribution (5-200 µm) with peaks at 10, 70 and 100 µm. This type of structure is favorable in reducing tortuosity, enhancing mass transport of oxygen and lithium ion and improving ionic conductivity. On the other hand, the structure of carbon paper comprises of non-woven short carbon fibers ( ̴ 15µm) and smaller pore size distribution range (10-70 µm) with a peak at 50 µm. This renders poor transport of oxygen from outside to the reaction sites leading to lower discharge capacity.The primary function of coating materials is to increase surface area of cathode thereby providing more reaction sites and creating tri-phase boundaries for reaction to take place. These catalysts also have different pore size distributions and resistance to mass transfer. Therefore, various carbon catalysts used yield different discharge capacity with same substrate.

Hybrid Redox Flow Cells with Enhanced Electrochemical Performance via Binderless and Electrophoretically Deposited Nitrogen-Doped Graphene on Carbon Paper Electrodes.

Hybrid redox flow cells (HRFC) are key enablers for the development of reliable large-scale energy storage systems; however, their high cost, limited cycle performance, and incompatibilities associated with the commonly used carbon-based electrodes undermine HRFC's commercial viability. While this is often linked to lack of suitable electrocatalytic materials capable of coping with HRFC electrode processes, the combinatory use of nanocarbon additives and carbon paper electrodes holds new promise. Here, by coupling electrophoretically deposited nitrogen-doped graphene (N-G) with carbon electrodes, their surprisingly beneficial effects on three types of HRFCs, namely, hydrogen/vanadium (RHVFC), hydrogen/manganese (RHMnFC), and polysulfide/air (S-Air), are revealed. RHVFCs offer efficiencies over 70% at a current density of 150 mA cm-2 and an energy density of 45 Wh L-1 at 50 mA cm-2, while RHMnFCs achieve a 30% increase in energy efficiency (at 100 mA cm-2). The S-Air cell records an exchange current density of 4.4 × 10-2 mA cm-2, a 3-fold improvement of kinetics compared to the bare carbon paper electrode. We also present cost of storage at system level compared to the standard all-vanadium redox flow batteries. These figures-of-merit can incentivize the design, optimization, and adoption of high-performance HRFCs for successful grid-scale or renewable energy storage market penetration.

Are Polyaniline and Polypyrrole Electrocatalysts for Oxygen (O2) Reduction to Hydrogen Peroxide (H2O2)?

In this report, we present results on the electrocatalytic activity of conducting polymers [polyaniline (PANI) and polypyrrole (PPy)] toward the electrochemical oxygen reduction reaction (ORR) to hydrogen peroxide (H2O2). The electropolymerization of the polymers and electrolysis conditions were optimized for H2O2 production. On flat glassy carbon (GC) electrodes, the faradaic efficiency (FE) for H2O2 production was significantly improved by the polymers. Rotating disc electrode (RDE) studies revealed that this is mainly a result of blocking further H2O2 to the water reduction pathway by the polymers. PPy on carbon paper (CP) significantly increased the molar production of H2O2 by over 250% at an average FE of above 95% compared to bare CP with a FE of 25%. Thus, the polymers are acting as catalysts on the electrode for the ORR, although their catalytic mechanisms differ from other electrocatalysts.

A multi-walled carbon nanotubes coated 3D printed anode developed for Biophotovotaic applications

We report a method for the design and fabrication of 3D printed bioanodes for Biophotovotaic (BPV) applications. Electrodes were fabricated in 5 different thicknesses, from 0.2 mm to 1.0 mm with a 0.2 mm increment and the electrodes were coated with multi-wall carbon nanotubes (MWCNTs). Electrochemical characterisation of these electrodes was performed and the performance tested alongside a bare carbon paper electrode in a bespoke designed membrane electrode assembly (MEA)-type BPV device.All of the MWCNTs-coated 3D printed electrodes outperformed the bare carbon paper electrode. The best performing one (1.0 mm) showed a 40 times increment in power density and a 20 times reduction of the internal resistance. The successful development of the 3D printed bioanode can be used as a standardised platform for the comparison of similar materials. The development of the electrodes and MEA-type BPV device will serve as the initial step towards the development of a monolithic 3D printed BPV platform.

Photoelectrochemical and photocatalytic detoxification of Cr(VI) to Cr(III) over terpyridine-derivatized Au nanoparticles on carbon paper and indium-tin-oxide electrodes

Detoxification of hexavalent chromium (Cr(VI)) in the environment and development of corresponding new materials and detoxification protocols have actively been studied and applied. Herein, 2,2′:6′,2′'-terpyridine-4′-thiol (STpy) was functionalized on Au nanoparticle (NP)-loaded carbon paper (CP) and indium-tin-oxide (ITO) electrodes (CP-AuNP and ITO-AuNP, respectively), and the photoelectrochemical (PEC) and photocatalytic detoxification of Cr(VI) using the resulting electrodes was investigated by cyclic voltammetry. Density functional theory at the B3LYP/6-31G level was used for geometry optimization, and the electronic energy state calculation was conducted at the TD-SCF/DFT/B3LYP level. For bare CP, ITO, and STpy-modified AuNP electrodes, the reduction potentials of Cr(VI) were around + 0.3, −0.2 V, and + 0.5 V (vs. Ag/AgCl), respectively. The PEC and photocatalytic Cr(VI) reduction performance of CP-AuNP was significantly improved upon STpy functionalization. Thus, these newly developed functionalized systems can provide very useful information for further improving the detoxification performances for various hazardous metals.

Nickel nanoparticles coated on the exfoliated graphene layer as an efficient and stable catalyst for oxygen reduction and hydrogen evolution in alkaline media

In this work, we report simultaneous electrochemical exfoliation of graphite powder using SDS, anionic surfactant salts, and cyclic potential to prepare graphene on carbon paper. Then, Nickel is electro-reduced into graphene nanosheets on carbon paper and also on the bare carbon paper to use in alkaline media for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). Afterward, graphene and Ni-graphene are characterized using scanning electron microscopy, atomic force microscopy (AFM) and electrochemical technique. SEM images show the Cauliflower structure of Ni in the absence of graphene and nanoparticle shapeless in the presence of smooth graphene. The electrochemical results show an excellent catalytic activity of Ni-graphene/ carbon paper with an over potential of 90 mV (Versus Ag/AgCl), which is lower than the literature value for Ni in alkaline electrolyte for HER (120 mV dec−1). The effect of graphene support on the electrochemical impedance spectroscopy response, activation energy and HER activity of the samples are investigated carefully. Finally, we prepare a novel gas diffusion electrode by using Ni pasted on carbon paper for the ORR in fuel cells and compared it with standard Pt/C catalysts using linear sweep voltammetry.

Investigation of CNT/PPy-Modified Carbon Paper Electrodes under Anaerobic and Aerobic Conditions for Phenol Bioremediation in Microbial Fuel Cells.

The study presents the comparative bioelectrochemical treatment of phenol in anodic and cathodic compartments of four identical dual chambered microbial fuel cells (MFCs) with bare and multiwalled carbon nanotube/polypyrrole (MWCNT/PPy)-coated electrodes, respectively. It was observed that systems performing biocathodic treatment of phenol performed better as compared to the systems performing bioanodic treatment. The maximum power densities for bioanodic phenol treatment using bare and coated electrodes were found to be 469.038 and 560.719 mW/m2, while for biocathodic treatment, they were observed to be 604.804 and 650.557 mW/m2, respectively. The MFCs performing biocathodic treatment of phenol consistently showed higher chemical oxygen demand removal efficiency, Coulombic efficiency, and power density and indicated the better performance of the biocathodic bare (B-MFC) and coated (C-MFC) MFCs as compared to the bioanodic B-MFC and C-MFC. UV/vis spectrophotometry revealed that the MWCNT/PPy-coated carbon paper worked significantly better in the treatment of phenol with admirable treatment obtained within a week of the experiment as compared to the system with bare carbon paper. Cyclic voltammetry asserted better electrochemical activity of the MFC systems with coated electrodes in the treatment of phenol. The electrochemical impedance spectroscopy data also supported the better performance of biocathodic phenol treatment with lower internal and charge transfer resistances. The scanning electron microscopy images confirmed the active biofilm formation on the electrode surface. The study indicates MFC as a viable option for the treatment of recalcitrant chemical compounds with energy recovery.

Facile preparation of polyelectrolyte-functionalized reduced graphene oxide for significantly improving the performance of microbial fuel cells

Poly(diallyldimethylammonium chloride)-functionalized reduced graphene oxide (PDDA-rGO) nanomaterials are fabricated by a facile ultrasonic blending method at room temperature and proposed as anodic electrocatalyst for microbial fuel cells (MFCs). PDDA serves as a noncovalent p-type dopant with strong electron-withdrawing ability, which is beneficial to readily attract electrons and further accelerate the rate of extracellular electron-transfer (EET) from the electrochemical active bacteria to the anode. Additionally, introduction of polyelectrolyte PDDA greatly increases the electroactive area and intensifies the biocompatibility of the anode. The electrochemical active microorganisms are effectively accumulated and a stable biofilm is rapidly formed. These factors result in the reduction of internal resistance and significantly enhance the power generation for MFCs, with the largest power density of 5029.3 mW m−2 (corresponding current density 11822.6 mA m−2), which is 2.51-fold and 5.46-fold of the unfunctionalized reduced graphene oxide (rGO) and bare carbon paper (CP) anodes, respectively. A facile preparation of anode materials at room temperature and the characteristics of remarkable biocurrent generation exhibit positive implication for the development of high performance MFCs.