Commercial Carbon Paper Research Articles

Anomalous CatalyticPerformance on Non-Active-Site Carbon Substrate.

Carbon-based nanomaterials are gaining attention in electrocatalysis. This study investigates the inherent nitrate reduction activity (NO3RR) of commercial carbon paper as a substrate. Results showed that carbon paper, without additional catalysts, achieved approximately 80.42% NH3Faradaic efficiency (FE) at -2.1 V vs. Hg/HgO in alkaline conditions, 83.51% NH3FE at -1.9 V vs. Ag/AgCl in neutral conditions, and 14.53% NH3FE at -1.9 V vs. MSE in acidic conditions. Density Functional Theory (DFT) calculations revealed energy barriers of 2.66 eV, 0.95 eV, and 1.37 eV, respectively. Molecular physisorption on the carbon paper surface generates an induced electric field, promoting charge transfer between the carbon paper and the adsorbed molecules, thus enhancing the activity of the carbon paper. These findings highlight the importance of considering the intrinsic catalytic properties of carbon substrates in catalyst design and evaluation, as overlooking these properties can lead to inaccurate performance assessments. This study emphasizes the need for a comprehensive approach to optimize catalytic systems.

Cornstalk-derived porous carbon as a high-performance and low-cost cathode for photoelectrochemical cell

Considering agricultural wastes as carbon source to be utilized for the preparation of porous carbon (PC), in particular with the advantages of low cost and abundant active sites, we construct a one-compartment membraneless photoelectrochemical cell use cornstalk-based PC as cathode instead of commercial carbon paper. The addition of as-prepared PC with high surface area at cathode is beneficial to provide a large number of reaction sites for H2O2 storing compared with commercial carbon paper. The maximum power density of this H2O2 fuel cell with PC/ITO-based cathode achieves 1.68 mW cm−2 under AM 1.5G solar light (1 sun, 100 mW cm−2) in 0.1 M HCl electrolyte at air atmosphere, which presents around 21.3- and 3.3-times enhancement compared to the cell with bare ITO-based cathode (0.079 mW cm−2) and the cell with carbon paper-based cathode (0.51 mW cm−2), respectively. Consequently, the calculated solar-to-electricity conversion efficiency (SECE) is as high as 1.04%. Furthermore, the cell can produce H2O2 from g-C3N4 on the photoanode side through photocatalytic H2O oxidation, and adsorptively store H2O2 on the cathode side by using of hierarchical nanostructures of PC with the disconnection of electrodes. After 0.5 h of light irradiation, the cell using H2O2 as the fuel operated by connecting the electrodes in the dark can form a specific capacitance of 19451.3 mF cm−2. We propose a pathway to utilize biomass-based PC as the cathode instead of commercial carbon paper in a one-compartment H2O2 fuel cell for the first time, which is unquestionably more promising for high-value use of agricultural wastes and the development of high-performance and low-cost fuel cells.

Synergistically improve the strength and porosity of carbon paper by using a novel phenol formaldehyde resin modified with cellulose nanofiber for proton exchange membrane fuel cells

To optimize the imbalance between the interfacial bonding and porosity properties of carbon paper (CP) caused by phenol formaldehyde resin (PF) impregnation, and therefore improve the performance of proton exchange membrane fuel cells (PEMFCs), a new approach through cellulose nanofibers grafted with methyl methacrylate (CNFM) as a modified reinforcement and pore-forming agent for PF is investigated. Through suppressing the methylene backbone fracture of CNFM-modified PF during its thermal depolymerization, the interfacial bonding between PF matrix carbon and carbon fibers is enhanced. Compared with unmodified CP, the in-plane resistivity of CNFM-modified CP is reduced by 35.78 %, while the connected porosity increases to 82.26 %, and more homogeneous pore size distribution (PSD) in the range of 20–40 μm is obtained for CNFM-modified CP. Besides, the tensile strength, flexural strength, and air permeability of CNFM-modified CP increase by 72.78 %, 298.4 %, and 103.97 %, respectively. In addition, CNFM-modified CP achieves the peak power density of PEMFCs to 701.81 mW·cm−2, exhibiting 10.98 % improvement compared with commercial CP (632.39 mW·cm−2), evidently achieving an integral promotion of CP and comprehensive performance.

Patterned hydrophobic gas diffusion layers for enhanced water management in polymer electrolyte fuel cells

Flooding of the cathode due to water accumulation is one of the biggest limiting factors in the performance of polymer electrolyte fuel cells (PEFCs). This study therefore attempts to solve this issue by fabricating gas diffusion layers (GDLs) with differently patterned hydrophobic regions. The GDLs in three different patterns (triangular, diamond, and inverted-triangular) were prepared by brushing a Polytetrafluoroethylene (PTFE) solution onto commercial carbon papers through a mask and tested in PEFCs. The patterned GDLs results in superior performance in all cases compared to a uniformly PTFE-treated GDL. Notably, the oxygen transport resistance is significantly reduced, indicating that the water accumulation in the cathode is avoided. This is attributed to the patterned hydrophobicity gradient providing distinct pathways for water and oxygen. The GDL with triangular patterning displays the highest peak power density, due to the fact that the untreated less hydrophobic region is in direct contact with the cathode outlet in this case, facilitating the removal of excess liquid water. Overall, the study confirms that the GDLs with patterned hydrophobicity could be used to enhance the performance of commercial PEFC systems by facilitating water management, potentially leading to improved efficiency and durability.

Inert is not inactive: origin of carbon dioxide electroreduction activity over a carbon current collector-based electrode

Commercial carbon paper (CP), a classical current collector, does not remain inert when subjected to CO2 electroreduction in a non-aqueous electrolyte.

Easily constructed porous silver films for efficient catalytic CO2 reduction and Zn-CO2 batteries.

For the electroreduction of carbon dioxide into high value-added chemicals, highly active and selective catalysts are crucial, and metallic silver is one of the most intriguing candidate materials available at a reasonable cost. Herein, through a novel two-step operation of Ag paste/SBA-15 coating and HF etching, porous silver films on a commercial carbon paper with a waterproofer (p-Ag/CP) could be easily fabricated on a large scale as highly efficient carbon dioxide reduction reaction (CO2RR) electrocatalysts with a CO Faraday efficiency (FECO) as high as 96.7% at -1.0 V vs. the reversible hydrogen electrode (RHE), and it still reaches up to 90% FECO over applied potentials ranging from -0.8 to -1.1 V vs. the RHE. Meanwhile, the membrane electrode assembly (MEA) utilizing the p-Ag/CP catalyst has achieved a current density, FECO, and stability of ∼60 mA cm-2, >91%, and 11 h, respectively. Furthermore, the assembled aqueous Zn-CO2 battery using p-Ag/CP cathode yielded a peak power density of 0.34 mW cm-2, 75 charge-discharge cycles for 25 h, and 64% FECO at 2.5 mA cm-2. Compared with flat Ag/CP, the significant enhancement in the CO2RR activity of p-Ag/CP was mainly attributed to the distinctive porous structure and an improved three-phase boundary, which is capable of inducing the stabilization of *COOH intermediates, increased active specific surface areas, fast electron transfer kinetic and mass transportation. Further, theoretical calculations revealed that p-Ag/CP possessed an optimized energy barrier for *COOH intermediates.

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.

PDIP/carbon paper photocatalyst sheet for enhanced photocatalytic water oxidation

Photocatalytic water splitting is a highly promising future energy technology. In contrast to the extensive work on particulate photocatalysts, there is still a lack of sufficient investigation for regularized photocatalysts. Here, from perylene diimide polymer (PDIP) and commercial carbon paper (CP), we develop a self-assembled PDIP/CP photocatalyst sheet that is easily scalable and can be used for photocatalytic water oxidation. Driven by strong interfacial π-π interactions, the PDIP spontaneously adsorbs onto the CP, which leads to a narrowed band gap, down-shifted VB edge, and enhanced separation of the photogenerated charge carriers of the PDIP. Under visible light, the PDIP/CP photocatalyst sheet shows significantly enhanced photocatalytic water oxidation activity (4 h cumulative oxygen evolution is 1.7 times higher than that of the powder-suspended system) and considerable cycling stability. The PDIP/CP photocatalyst sheet has the potential for large-scale device applications.

Development and Scale-up of High Performance Electrodes for Vanadium Redox Flow Batteries

Vanadium redox flow battery (VRFB) is a promising technology for energy storage because of its independent energy to power ratio and long cycle life. However, VRFB commercialization is still hindered by some technological issues, among which the limited power density. This results in increased cell area and system costs.In order to tackle this issue is fundamental to boost the sluggish electrode kinetic. In the literature different wet processes, such as acid treatments, have been widely employed to add catalytic functionalities to commercial carbon electrodes [1,2]. Also plasma etching or plasma doping have been adopted for the improvement of electrode performance [3]. Recently, the introduction of heteroatoms is becoming one of the most common method to enhance the catalytic activity of carbon electrodes. Zhao et al. [21] performed thermal treatment of graphite felt combined with electrochemical deposition of Bismuth nanoparticles, obtaining 80% energy efficiency at 600 mA cm-2. Li et al. [22] developed a hierarchical nitrogen doped electrode, reaching 76.8% energy efficiency at 400 mA cm-2.In this work it is proposed a prototypal deposition method, called NanoJeD. It is a high throughput, dry and easily scalable process starting from gas phase. It consists in radiofrequency (RF) plasma operating in dusty mode, through which a non-flammable mixture of Acetylene and Argon is fluxed and the RF plasma ignites the decomposition and clasterization of the Acetylene. The former nanoparticles, following the gas streamline are dragged to a high aspect ratio orifice and ejected in a low-pressure chamber where a substrate is placed. Kinetic energy of the nanoparticles ejected in the chamber defines their impact energy with the substrate and the consequent collection mechanism. Subsequently, a vacuum thermal treatment is performed and this two-steps process allows a fine tuning of the material properties and the formation of a carbon allotropes with catalytic peculiarities known as Carbon Nano Onions (CNOs).Deposited CNOs were firstly characterized with Raman spectroscopy, Scanning Electrode Microscopy (SEM) and Transmission Electrode Microscopy (TEM). Electrochemical characterization was performed in a three-electrode setup with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CNOs exploit their unique properties: high conductivity, high chemical-mechanical stability, and catalytic activity towards redox reactions. The peculiarities of CNO reside in the edge of graphene sheet, which is ascertained to share a higher catalytic activity with respect to the basal plane of the same graphene sheet [6].Afterwards CNOs were deposited on a commercial carbon paper electrode, Sigracet® SGL 39 AA (nominal thickness of ∼290 μm), that was tested in 4 cm2 symmetric cell with Nafion® 211, permitting to evaluate the effect of CNOs on both positive and negative electrode. Subsequently, full cell test at different current densities was performed in cycles with fixed cut-off voltages (1-1.65 V), obtaining an energy efficiency of 81% and 74% at 400 mA cm-2 and 600 mA cm-2, respectively. The corresponding electrolyte utilization was 70% and 59%. Moreover, electrode stability has been evaluated during 1’000 cycles operation.Finally, the process has been scaled-up permitting to obtain a 100 cm2 electrode. The corresponding full cell test with Nafion® 212 resulted in 75% energy efficiency at 0.3 A cm-2.

Measuring the through-plane and in-plane oxygen apparent diffusion coefficients in the gas diffusion layer

Accurately predicting oxygen mass transport resistance and current distribution in fuel cells requires significant knowledge of oxygen diffusion coefficients in both in-plane and through-plane directions. However, there are few methods for measuring in-plane oxygen diffusion coefficients, which are important parameters for simulating oxygen flux distribution in gas diffusion layers (GDLs). In this study, we establish measurement methods and calculations for both in-plane and through-plane oxygen diffusion coefficients. Using in-house designed cells, we measure the in-plane and through-plane oxygen apparent diffusion coefficients of a commercial carbon paper (AvCarb EP40) at various torques and gas flow rates. We also simulate oxygen flux distributions in the GDL under each torque and gas flow rate. Our results show that the channel part is the major contributor to total oxygen flux at high torque conditions and that an increase in torque leads to a decrease in the contribution from the land part. Simulation results also suggest that a higher gas flow rate and lower torque contribute to a more uniform distribution of oxygen flux in the GDL.

Performance Enhancement of Proton Exchange Membrane Fuel Cell through Carbon Nanofibers Grown In Situ on Carbon Paper

We developed an integrated gas diffusion layer (GDL) for proton exchange membrane (PEM) fuel cells by growing carbon nanofibers (CNFs) in situ on carbon paper via the electro-polymerization of polyaniline (PANI) on carbon paper followed by a subsequent carbonization treatment process. The CNF/carbon paper showed a microporous structure and a significantly increased pore volume compared to commercial carbon paper. By utilizing this CNF/carbon paper in a PEM fuel cell, it was found that the cell with CNF/carbon paper had superior performance compared to the commercial GDL at both high and low humidity conditions, and its power density was as high as 1.21 W cm-2 at 100% relative humidity, which is 26% higher than that of a conventional gas diffusion layer (0.9 W cm-2). The significant performance enhancement was attributed to a higher pore volume and porosity of the CNF/carbon paper, which improved gas diffusion in the GDL. In addition, the superior performance of the cell with CNF/carbon paper at low relative humidity demonstrated that it had better water retention than the commercial GDL. This study provides a novel and facile method for the surface modification of GDLs to improve the performance of PEM fuel cells. The CNF/carbon paper with a microporous structure has suitable hydrophobicity and lower through-plane resistance, which makes it promising as an advanced substrate for GDLs in fuel cell applications.

Computer-aided determination of the effective diffusion coefficient of a gas diffusion layer for polymer electrolyte fuel cells

Accurate measurement of the gas diffusivity in a gas diffusion layer (GDL) for polymer electrolyte fuel cells (PEFCs) is extremely important in order to improve the performance of PEFCs and design fuel cell stacks. In the present study, in order to improve the accuracy in the determination of the gas diffusivity when uisng the simple and inexpensive method newly proposed by Yoshimune (2022), which uses an infrared absorption carbon dioxide sensor, three-dimensional (3D) simulations reproducing the experiments are performed. The results reveal that the gas transport resistance of the measurement apparatus is not small (approximately seven times higher than that of a commercial carbon paper (TGP-H060, Toray)), and the 3D simulation, which considers the resistance, reduces the error in the effective diffusion coefficient of the GDL by 25%. The effective diffusion coefficient for a new sample can be determined using the simulation results already obtained, when the apparatus is unchanged. In addition, a new one-dimensional (1D) model extended from the simple 1D model presented in Yoshimune (2022) is proposed. Since the extended model incorporates the gas transport resistance of the apparatus and dispenses with the generation of computational grids and the use of an expensive computer needed in conducting 3D simulations, this model enables us to obtain the accurate effective diffusion coefficient of a GDL with ease even when using a measurement apparatus with different sizes.

High-performance direct liquid fuel cells benefited from highly N-doped and defect-rich carbon paper cathode with carbon nanosheets

Persulfate is a potential oxidant in direct liquid fuel cells (DLFCs), and the commercial carbon paper (CP) can directly serve as the cathode due to strong oxidizability of persulfate. However, the poor catalytic activity and low specific surface area of CP limit the electrode performance. Herein, a defect-enriched, pyridine-N-dominated and self-standing carbon paper electrode with abundant carbon nanosheets is successfully prepared by hydrothermal treatment combined with in-situ electrochemical exfoliation. Benefitting from the integrated structure, plentiful defects and high-content pyridine-N dopants of the prepared electrode result in the superior electrocatalytic activity and long-term stability in persulfate reduction reaction. Remarkably, a membraneless DLFC with the prepared electrode as cathode and persulfate as the oxidant acquires prominent cell performance and extremely high open circuit voltage of 2.13 V. The maximum power density of the DLFC achieves 241.0 mW cm−2, far higher than those of the previously reported similar membraneless DLFCs. A three-dimensional computational model for the DLFC is developed, which is help to reveal the importance of improving the reaction kinetics and electrical conductivity for the cathode with persulfate as oxidant. A facile approach for in-situ preparation of highly N-doped CP electrode is provided to yield outstanding cell performance for low-cost DLFCs.

3D Composite PDMS/MWCNTs Aerogel as High-Performing Anodes in Microbial Fuel Cells

Porous 3D composite materials are interesting anode electrodes for single chamber microbial fuel cells (SCMFCs) since they exploit a surface layer that is able to achieve the correct biocompatibility for the proliferation of electroactive bacteria and have an inner charge transfer element that favors electron transfer and improves the electrochemical activity of microorganisms. The crucial step is to fine-tune the continuous porosity inside the anode electrode, thus enhancing the bacterial growth, adhesion, and proliferation, and the substrate's transport and waste products removal, avoiding pore clogging. To this purpose, a novel approach to synthetize a 3D composite aerogel is proposed in the present work. A 3D composite aerogel, based on polydimethylsiloxane (PDMS) and multi-wall carbon nanotubes (MWCNTs) as a conductive filler, was obtained by pouring this mixture over the commercial sugar, used as removable template to induce and tune the hierarchical continuous porosity into final nanostructures. In this scenario, the granularity of the sugar directly affects the porosities distribution inside the 3D composite aerogel, as confirmed by the morphological characterizations implemented. We demonstrated the capability to realize a high-performance bioelectrode, which showed a 3D porous structure characterized by a high surface area typical of aerogel materials, the required biocompatibility for bacterial proliferations, and an improved electron pathway inside it. Indeed, SCMFCs with 3D composite aerogel achieved current densities of (691.7 ± 9.5) mA m-2, three orders of magnitude higher than commercial carbon paper, (287.8 ± 16.1) mA m-2.

Impact of Porous Microstructure on Performance of Redox Flow Batteries: A Modeling Study

Electrodes are essential components of redox flow batteries (RFBs) that determine performance. Given the advances in 3D printing technologies, bottom-up design and manufacturing electrodes with controllable and reproducible properties can be attainable. In this study, pore network modeling is utilized to understand the coupled transport and reaction processes in Hydrogen-Bromine (H2/Br2) flow batteries. This study highlights the importance of the microstructure while designing a 3D printable microstructure. The 3D pore-scale model is validated against the experimental measurements using an unstructured pore network, extracted from a tomography scan of a commercial carbon paper. A printable ordered cubic lattice with the same permeability as carbon paper increases the maximum power density by 35% due to lower tortuosity and higher mass transport. A parametric study is carried out to understand the role of microstructure, such as pore size, throat size, anisotropy, and lattice unit size, for flow-through and interdigitated flow fields. It is shown that a smaller lattice unit, increases the reactive surface area, lowers the activation and mass transport overpotentials, and consequently enhances the performance of the battery. An improved microstructure design for both flow fields is proposed that intensifies the performance of the battery via engineering the flow path of the electrolyte.

Surface engineering towards high-energy carbon cathode for advanced aqueous zinc-ion hybrid capacitors

Opportunities coexist with challenges for the development of carbon-based cathodes with a high energy density applied for zinc ion hybrid capacitors (ZIHCs). In the present study, a facile and effective surface engineering approach is demonstrated to greatly improve the energy storage ability of commercial carbon paper (CP) in ZIHC. Benefiting from the introduced oxygen functional groups, larger surface area and improved surface wettability upon air calcination, the assembled aqueous ZIHC with the functionalized carbon paper (FCP) exhibits a much higher areal capacity of 0.22 mAh/cm2 at 1 mA/cm2, outperforming the counterpart with blank CP by over 5000 times. More importantly, a superior energy density and power density of 130.8 µWh/cm2 and 7460.5 µW/cm2, are respectively delivered. Furthermore, more than 90% of the initial capacity is retained over 10000 cycles. This surface engineering strategy to improve the energy storage capability is potentially applicable to developing a wide range of high-energy carbon electrode materials.

Rational Placement of Catalysts for Oxygen Reduction and Evolution Reactions Based on the Reaction Sites in Porous Gas Diffusion Electrodes

Metal-air secondary batteries using alkaline electrolyte solutions are promising candidates for next-generation large-scale energy storage systems because of their potential high capacity, low cost, and high safety standard. However, large overpotential of bifunctional air electrodes hindered their wide applications. Recently, increasing research on electrocatalysts for oxygen reduction reaction (ORR) and oxygen reduction reaction (OER) has been conducted to reduce the overpotential, and many active catalysts have been developed. On the other hand, formation of reaction sites is also important since the reaction sites for ORR and OER are basically different1. In this work, we investigated the reaction sites in porous gas diffusion electrodes (GDE) and constructed a GDE with a double-layered catalyst layer based on the difference in the reaction sites for ORR and OER2.La0.6Ca0.4CoO3 (LCCO, bifunctional catalyst), La0.4Sr0.6MnO3 (LSMO, ORR catalyst) and Ca2FeCoO5 (CFCO, OER catalyst) were synthesized by the polymerized complex method. Porous gas diffusion electrodes are constructed by the hot-press method. Catalyst layers were composed of the prepared catalyst (50 wt%), graphitized carbon black (35 wt%), and poly(tetrafluoroethylene) (15 wt%). Gas diffusion layers (GDL) were commercial carbon papers (TGP-H-030H, Chemix). IR-corrected polarization curves were measured by the constant current and AC impedance measurements. Oxygen diffusion resistances for ORR and OER were estimated from the difference in the steady-state potential between pure oxygen and air atmosphere (⊿E = |E O2 – Eair|). Larger increase in ⊿E indicates larger oxygen diffusion resistances in the oxygen reaction processes3.Figure 1 (a, b) shows ⊿E-I curves of LCCO-GDE for ORR and OER in 4.0 and 8.0 dm–3 KOHaq. The oxygen permeability(D O2×C O2) in 4.0 dm–3 KOHaq is 16 times as large as that in 8.0 dm–3 KOHaq while the ion conductivities of these electrolyte solutions are at the same extent. The increase in ⊿E for ORR was larger in 8.0 dm–3 KOHaq, indicating dissolved oxygen involved in the ORR process. In contrast, the ⊿E for OER was nearly negligible in these electrolyte solutions, suggesting that oxygen was mainly transported as bubbles. We also measured ⊿E-I curves of the LCCO-GDE in 8.0 dm–3 KOHaq having different catalyst layer thicknesses. The increases in ⊿E were almost independent of the catalyst layer thicknesses for ORR and OER, suggesting that the reaction sites were concentrated in the catalyst layer. Finally, we compared polarization curves of the GDEs with single-layered catalyst layer (LSMO+CFCO|DGL-GDE) and double-layered catalyst layers (LSMO|CFCO|GDL-GDE and CFCO|LSMO|GDL-GDE) to identify the reaction sites for ORR and OER (Fig. 1 (c, d)). The smallest overpotential of CFCO|LSMO|GDL-GDE for both ORR and OER showed that the reaction sites for ORR and OER were concentrated at the electrolyte-side and gas-side, respectively. In addition, CFCO|LSMO|GDL-GDE showed higher durability than LSMO+CFCO|DGL-GDE. From these results, it can be concluded that the placement of the ORR and OER catalysts on the electrolyte-side and gas-side of the CL can improve both activity and durability of the bifunctional air electrode.

Microstructures and electrical conductivity properties of compressed gas diffusion layers using X-ray tomography

Bulk resistance of the gas diffusion layer (GDL) plays an important role in the ohmic loss of proton exchange membrane fuel cells (PEMFCs). This work represents the first direct experimental study and comparison of the bulk resistances during the compression process of commonly used commercial GDLs, carbon paper and carbon felt, from the perspective of the microstructure mechanisms. The in-situ X-ray tomography and a fiber tracing algorithm are used to obtain the microstructure characteristics of compressed GDLs. The through-plane (T-P) and in-plane (I-P) bulk resistances of GDLs are measured by the microelectrode probe measurement method and the four-point probe method, respectively. Then, their resistivities are calculated. For the T-P direction, the arrangement of fibers gradually becomes compact during the compression, arousing the nearly linear increase of fiber contact points. Thus, more and more conductive paths are constructed, inducing a rapid decline of the T-P bulk resistivity. Since the fibers in carbon felt are entangled together, the fibers in the edge areas are arranged loosely at low compression. This uneven distribution of contact points in carbon felt results in much larger T-P bulk resistivity than that of carbon paper at low compressive strain. For carbon paper, binders contribute significantly to the smaller T-P resistivity because they tend to gather at the fiber intersections, which forms more conductive paths with better conductivity. For the I-P direction, the bulk resistivities of GDLs decrease linearly during compression. The nearly horizontal fibers are the key to the I-P bulk resistivity, and both smaller fiber density and higher fiber tortuosity lead to the increase of the I-P bulk resistivity. This study helps to understand the microstructure mechanisms of the bulk resistances of various GDLs during the compression process, which can guide the design and fabrication process of GDLs.

How to Design a 3D Ordered Microstructure for Redox Flow Batteries: A Pore Network Modeling Study

Amid growing energy demand and the progressive contribution of intermittent renewable energy, the need for large-scale energy storage systems have become critical. Redox flow batteries can be a legitimate choice to store a huge amount of energy, subject to further improvement in their components, specifically the porous electrode. 3D printing technology is a viable method to manufacture porous electrodes with an engineered design and controllable properties. Attaining this goal requires an understanding of the effect of electrode microstructure which this study strove to provide. The effect of different parameters, including pore size, throat size, frequency of lattice units, and permeability anisotropy in the through-plane and in-plane directions were investigated in the flow-through as well as interdigitated batteries.Pore network modeling was utilized to investigate the effect of microstructure on the performance of Hydrogen-Bromine (H2-Br2) flow batteries. Simulations were carried out under steady-state conditions for electrolyte transport, species transport, and charge transport. To isolate the role of microstructure on the performance of the battery, simulations were performed at the constant flow condition in which the advective force was constant.The simulations were validated against the experimental study using an unstructured pore network, extracted from a tomography scan of a commercial carbon paper. A 3D printed ordered cubic lattice with the same permeability of the carbon paper showed a better performance. This was mainly achieved by better mass transport as a result of higher advection, diffusion, and lower tortuosity of the ordered lattice.It was found that a combination of bigger pores and smaller throats at constant permeability, facilitated the diffusion rate especially in the in-plane direction, as well as, increased the specific surface area of the network. It was also shown that a larger number of lattice units, resulted in a higher surface area, consequently a higher current generation.For both of the flow-through and interdigitated flow fields, permeability change in the through-plane direction (x-direction and y-direction) at the constant flow rate condition, almost did not affect the performance of the battery. However, the latter drastically changed the required electrolyte supplying pressure that could translate into a more economically feasible process. The permeability variation in in-plane direction reinforced or hampered the diffusion and also the current generation.Finally, an improved design of microstructure for the flow-through and interdigitated batteries were proposed and investigated. The specific surface area, permeability, and flow rate were kept constant to solely observe the role of microstructure on the battery performance. Results presented the superior performance of the improved microstructure in both flow fields. It was achieved by deviating the electrolyte main flow path, to the proximity of the membrane, where more reactions were taking place. This study took an initial step and provided insight into designing and manufacturing a porous electrode using 3D printing technologies. However, it can be continued in various paths including using complex 3D pore structures rather than simple cylindrical lattice to optimize the hydrodynamic behavior of the electrolyte and the specific surface area of the electrode.

Chemical bonding of flexible graphene to carbon paper: A new synthetic paradigm for freestanding electrode with high capacitive deionization performance

Capacitive deionization (CDI) has become a promising desalination and water treatment technology due to its low-cost, environment-friendliness and energy-efficient. In this work, it is successful to achieve the preparation of high-quality three-dimensional flexible graphene frameworks (3DFGFs) from commercial carbon paper (CP) by simply combining the modified Hummer's method with freezing drying technology. The electroactive area, conductivity and hydrophilicity are greatly improved, the areal specific capacitance of 3DFGFs electrode reaches 1.43 F/cm2 at 10 mV/s in 1 M NaCl solution, and the areal adsorption capacity is up to 322.21 (50 mg/L NaCl) and 581.51 mg/m2 (500 mg/L NaCl), respectively. Interestingly, the overall shape of the 3DFGFs electrode remain intact after 500 times of crimping (capacity retention rate is 96.85% for >500 crimping), suggesting that 3DFGFs have outstanding flexibility owing to the strong interaction between the fibers and the graphene sheets in the frameworks. Finally, we propose a concept of how-to recovery the electrical energy stored in CDI cell. This work opens up a promising direction for the preparation of flexible CDI electrodes, and the simple and mild method developed can be easily applied to the preparation of other flexible electrodes.