Monolithic Electrodes Research Articles

Self-supported Hierarchical Nanoporous Cu/Mo@MoOx Hybrid Electrodes as Robust Nonprecious Electrocatalysts for High-efficiency Hydrogen Evolution

Background: The hydrogen evolution reaction is a crucial step in electrochemical water splitting to generate molecular hydrogen with high purity, but it usually suffers from a sluggish reaction kinetics in alkaline media because of additional water dissociation and/or improper adsorption energy of reactive hydrogen intermediates. It is desirable to design highly active and robust nonprecious electrocatalysts as alternatives to state-of-the-art commercially available Pt/C catalysts for large-scale hydrogen production via water-alkali electrolysis. Methods: We developed monolithic nanoporous hybrid electrodes composed of electroactive Mo@MoOx nanoparticles, which are seamlessly integrated on hierarchical nanoporous Cu scaffold (Cu/Mo@MoOx) by making use of a spontaneous phase separation of Mo nanoparticles and subsequently, self-grown MoOx in chemical dealloying. Results: Owing to the unique monolithic electrode architecture, in which the constituent Mo@MoOx nanoparticles work as electroactive sites and the hierarchical nanoporous Cu skeleton serves as fast electron-transfer and mass-transport pathways, the monolithic nanoporous Cu/Mo@MoOx hybrid electrode exhibits superior electrocatalysis in 1 M KOH, with a low Tafel slope of 66 mV dec−1 and outstanding stability. It only takes them ~185 mV overpotential to reach −400 mA cm−2, ~150 mV lower than that of nanoporous Cu supported Pt/C. Conclusion: The outstanding electrochemical performance and excellent structural stability make nanoporous Cu/Mo@MoOx electrodes attractive alternatives to Pt/C catalysts in alkaline-based devices.

Nanoenabled Bioelectrical Modulation.

ConspectusStudying the formation and interactions between biological systems and artificial materials is significant for probing complex biophysical behaviors and addressing challenging biomedical problems. Bioelectrical interfaces, especially nanostructure-based, have improved compatibility with cells and tissues and enabled new approaches to biological modulation. In particular, free-standing and remotely activated bioelectrical devices demonstrate potential for precise biophysical investigation and efficient clinical therapies. Interacting with single cells or organelles requires devices of sufficiently small size for high resolution probing. Nanoscale semiconductors, given their diverse functionalities, are promising device platforms for subcellular modulation. Tissue-level modulation requires additional consideration regarding the device’s mechanical compliance for either conformal contact with the tissue surface or seamless three-dimensional (3D) biointegration. Flexible or even open-framework designs are essential in such methods. For chronic organ integration, the highest level of biocompatibility is required for both the materials and device configurations. Additionally, a scalable and high-throughput design is necessary to simultaneously interact with many individual cells in the organ. The physical, chemical, and mechanical stabilities of devices for organ implantation may be improved by ensuring matching of mechanical behavior at biointerfaces, including passivation or resistance designs to mitigate physiological impacts, or incorporating self-healing or adaptative properties.Recent research demonstrates principles of nanostructured material designs that can be used to improve biointerfaces. Nanoenabled extracellular interfaces were frequently used for either electrical or remote optical modulation of cells and tissues. In particular, methods are now available for designing and screening nanostructured silicon, especially chemical vapor deposition (CVD)-derived nanowires and two-dimensional (2D) nanostructured membranes, for biological modulation in vitro and in vivo. For intra- and intercellular biological modulation, semiconductor/cell composites have been created through the internalization of nanowires, and such cellular composites can even integrate with living tissues. This approach was demonstrated for both neuronal and cardiac modulation.At a different front, laser-derived nanocrystalline semiconductors showed electrochemical and photoelectrochemical activities, and they were used to modulate cells and organs. Recently, self-assembly of nanoscale building blocks enabled fabrication of efficient monolithic carbon-based electrodes for in vitro stimulation of cardiomyocytes, ex vivo stimulation of retinas and hearts, and in vivo stimulation of sciatic nerves.Future studies on nanoenabled bioelectrical modulation should focus on improving efficiency and stability of current and emerging technologies. New materials and devices can access new interrogation targets, such as subcellular structures, and possess more adaptable and responsive properties enabling seamless integration. Drawing inspiration from energy science and catalysis can help in such progress and open new avenues for biological modulation. The fundamental study of living bioelectronics could yield new cellular composites for diverse biological signaling control. In situ self-assembled biointerfaces are of special interest in this area as cell type targeting can be achieved.

Hybrid heterojunction of molybdenum disulfide/single cobalt atoms anchored nitrogen, sulfur-doped carbon nanotube /cobalt disulfide with multiple active sites for highly efficient hydrogen evolution

A multicomponent 3D monolithic electrode was designed that consists of Co single atoms anchored/nitrogen, sulfur co-doped carbon nanotubes (CoSAs-NS-CNTs) on carbon cloth (CC) with ultra-thin MoS2 nanosheets externally decorated and ultra-small CoS2 nanodots internally confined (MoS2/CoSAs-NS-CNTs@CoS2/CC) to form a hybrid heterojunction electrode with double interfaces as vectorial electron transport pathways for promoting electrocatalytic performance. The integration of well-distributed MoS2 nanosheets and CoS2 nanodots linked with Co single atoms anchored/N, S co-doped CNTs endows abundant multiple active sites, outstanding conductivity, and the downshifted d-band center with a thermodynamically favorable hydrogen adsorption free energy (ΔGH*) for effectively catalyzing hydrogen evolution reaction (HER). As a result, the optimal MoS2/CoSAs-NS-CNTs@CoS2/CC electrode exhibits outstanding HER performance with overpotentials of 72 and 56 mV at 10 mA cm−2 and small Tafel slopes of 59.4 and 43.2 mV dec-1 in acidic and alkaline solutions, respectively, outperforming most of the previously reported molybdenum/cobalt sulfide-based electrocatalysts. Moreover, the electrode also displays good durability and stability reflected from the small decrease on activity after 5000 CV cycles and nearly no decay in current density after electrolysis for 20 h.

Surface Phosphorus-Induced CoO Coupling to Monolithic Carbon for Efficient Air Electrode of Quasi-Solid-State Zn-Air Batteries.

One challenge facing the development of air electrodes for Zn–air batteries (ZABs) is the embedment of active sites into carbon, which requires cracks and blends between powder and membrane and results in low energy efficiency during manufacturing and utilization. Herein, a surface phosphorization‐monolithic strategy is proposed to embed CoO nanoparticles into paulownia carbon plate (P–CoO@PWC) as monolithic electrodes. Benefiting from the retention of natural transport channels, P–CoO@PWC‐2 is conducive to the construction of three‐phase interface structure for efficient mass transfer and high electrical conductivity. The electrode exhibits remarkable catalytic activities for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with a small overpotential gap (E OER − E ORR = 0.68 V). Density functional theory calculations reveal that the incorporation of P on P–CoO@PWC‐2 surface adjusts the electronic structure to promote the dissociation of water and the activation of oxygen, thus inducing catalytic activity. The monolithic P–CoO@PWC‐2 electrode for quasi‐solid‐state or aqueous ZABs has excellent specific power, low charge–discharge voltage gap (0.83 V), and long‐term cycling stability (over 700 cycles). This work serves as a new avenue for transforming abundant biomass into high‐value energy‐related engineering products.

Wood-Derived, Conductivity and Hierarchical Pore Integrated Thick Electrode Enabling High Areal/Volumetric Energy Density for Hybrid Capacitors.

For the proliferation of the supercapacitor technology, it is essential to attain superior areal and volumetric performance. Nevertheless, maintaining stable areal/volumetric capacitance and rate capability, especially for thick electrodes, remains a fundamental challenge. Here, for the first time, a rationally designed porous monolithic electrode is reported with high thickness of 800 µm (46.74mg cm-2 , with high areal mass loading of NiCo2 S4 6.9mg cm-2 ) in which redox-active Ag nanoparticles and NiCo2 S4 nanosheets are sequentially decorated on highly conductive wood-derived carbon (WC) substrates. The hierarchically assembled WC@Ag@NiCo2 S4 electrode exhibits outstanding areal capacitance of 6.09 F cm-2 and long-term stability of 84.5% up to 10 000 cycles, as well as exceptional rate capability at 50mA cm-2 . The asymmetric cell with an anode of WC@Ag and a cathode of WC@Ag@NiCo2 S4 delivers areal/volumetric energy density of 0.59 mWh cm-2 /3.93 mWh cm-3 , which is much-improved performance compared to those of most reported thick electrodes at the same scale. Theoretical calculations verify that the enhanced performance could be attributed to the decreased adsorption energy of OH- and the down-shifted d-band of Ag atoms, which can accelerate the electron transport and ion transfer.

Ultrasonically Surface-Activated Nickel Foam as a Highly Efficient Monolith Electrode for the Catalytic Oxidation of Methanol to Formate.

Most of the current electrocatalysts for the methanol oxidation reaction are precious group metals such as Pt, Pd, and Ru. However, their use is limited due to their high cost, scarcity, and issues with carbon monoxide poisoning. We developed a simple method to prepare a nickel foam (NF)-based monolith electrode with a NiO nanosheet array structure as an efficient electrocatalyst toward the oxidation of methanol to produce formate. By a simple ultrasonic acid treatment and air oxidation at room temperature, an inert NF was converted to NiO/NF as a catalytically active electrode due to the uniform NiO nanosheet array that was rapidly formed on the surface of NiO/NF. In alkaline electrolytes containing methanol, the as-prepared NiO/NF catalysts exhibited a lower methanol oxidation reaction (MOR) potential of +1.53 V vs RHE at 100 mA cm-2 compared to that of inert NF samples. The difference in potentials between the EMOR and the EOER at that current density was found to be 280 mV, indicating that methanol oxidation occurred at lower potentials as compared to the oxygen evolution reaction (OER). We also observed that the NiO/NF could also efficiently catalyze the oxidation of CO without being poisoned by it. NiO/NF retained close to 100% of its initial activity after 20,000 s of methanol oxidation tests at high current densities above 200 mA cm-2. Because of the simple synthesis method and the enhanced catalytic performance and stability of NiO/NF, this allows methanol to be used as an OER masking agent for the energy-efficient generation of value-added products such as formic acid and hydrogen.

Synthesis and investigation on microstructure and electrical conductivity of Ruddlesden-Popper phase, La1.9Sr0.1Ni0.7Cu0.3O4 (LSNC), as cathode material for intermediate temperature solid oxide fuel cells

In the present work, a Ruddlesden-Popper oxide, La1.9Sr0.1Ni0.7Cu0.3O4 (LSNC), has been synthesized by solid state reaction for Intermediate-Temperature Solid Oxide Fuel Cells (IT-SOFCs) applications. To investigate the effect of sintering temperature on the microstructure and electrical properties, the LSNC cathode samples were fired in the temperature range of 1000–1300 °C. The crystal structure and microstructures of the synthesized and fired samples were studied by XRD and SEM, respectively. The electrical conductivity of the monolithic electrodes is investigated experimentally through the four-probe method as a function of temperature in the range of 300 – 800 oC. Our investigation revealed that the LSNC material behaves like semiconductor materials; the conductivity increases by increasing the temperature up to a specific temperature but then decreases with further temperature increases. It has also been proven that an increase in sintering temperature leads to increasing electrical conductivity. The maximum total electrical conductivity of 67.57 S cm−1 at 450 °C was recorded for pure LSNC material sintered at 1300 °C.

Investigation of H2SO4 and KOH aqueous electrolytes on the electrochemical performance of activated carbon derived from areca catechu husk

Aqueous electrolytes have shown great interest in developing high performance and environmentally friendly supercapacitors. This work focuses on systematic investigations of the symmetrical properties of activated carbon electrode for supercapacitors in different aqueous electrolytes. Here, we compare the performance of supercapacitors using 1M KOH and 1M H2SO4 different electrolytes based on carbon monolith electrodes derived from areca catechu husk waste. Carbon electrodes were synthesized using single-step pyrolysis both carbonization and physical activation without the addition of synthetic adhesive materials. The electrochemical properties were evaluated based on the cyclic voltammetry method at voltage windows of 0-0.5V and 0-1.0V with a scanning rate of 1 mV s−1, 2 mV s−1, 5 mV s−1, and 10 mV s−1. The electrode supercapacitor showed the highest specific capacitance of 150 F g−1 and 112 F g−1 at a scanning rate of 1 mV s−1 for H2SO4 and KOH electrolytes respectively. The maximum specific energy was found as high as 20.97 Wh kg−1 and the specific power of 75.57 kW kg−1 at the voltage window of 0-1.0V were achieved for H2SO4 electrolytes. As addition, the physical properties of carbon electrode also characterized such as mass, volume, and density. This work provides consideration the selected of different aqueous electrolytes for high-performance supercapacitors.

Constructing monolithic sulfur cathodes with multifunctional N,P dual-doped carbon nanocages to achieve high-areal-capacity lithium-sulfur batteries

Despite the great progress achieved, lithium-sulfur (Li-S) batteries still suffer unsatisfactory performance at high sulfur loading (>5 mg cm−2), which results from the impeded kinetics in charge transfer and polysulfides conversion with increasing electrode thickness. Herein, we have constructed a high-sulfur-loading monolithic cathode by in-situ reducing graphene oxide (GO) in the aqueous solution with dispersed sulfur-filled N,P dual-doped carbon nanocages (NPCNC). The Li-S battery with the areal sulfur loading of 6 mg cm−2 exhibits a high areal capacity of 6.7 mAh cm−2 and a retention of 4.2 mAh cm−2 after 250 cycles. The excellent performance is attributed to the synergism of the facilitated charge transfer and alleviated polysulfide diffusion by the reduced GO-framed 3D network, and the suppressed shuttle and polarization effects by the confinement and electrocatalysis of NPCNC. In addition, the monolithic sulfur electrode is free from binder, conductive agent and current collector, much beneficial to gravimetric performance. This study demonstrates an efficient strategy to increase the areal performance of Li-S batteries.

A nickel-nitrogen-doped carbon foam as monolithic electrode for highly efficient CO2 electroreduction

Carbon materials are considered as one of the most promising electrocatalysts for the electrochemical CO2 reduction which can convert CO2 to value-added chemical products in a clean, cheap and efficient manner. However, the carbon-based catalysts still suffer from low partial current density under high Faradaic efficiency of products, which results from their poor intrinsic electrocatalytic activity and the use of insulating binders. Herein, we design a novel monolithic electrocatalyst by combining the carbon foam with Ni-Nx active sites, which possesses high electrical conductivity, low mass transfer resistance and abundant active sites. Benefiting from these structural advantages, this monolithic electrocatalyst exhibits a large partial current density (71.6 mA cm−2 at -1.4 V versus reversible hydrogen electrode) and a stable Faradaic efficiency of CO (>90 %) at the applied potential range from -1.0 to -1.4 V.

Oxygen-deficient Cu doped NiFeO nanosheets hydroxide as electrode material for efficient oxygen evolution reaction and supercapacitor

The development of renewable energy conversion and storage has triggered the development of electrode materials for oxygen evolution reaction (OER) and supercapacitors. Here we report a highly active Cu doped NiFe nanosheets hydroxide electrode with rich oxygen vacancies (OVs) (denoted as H-NiFeCuO/NF) prepared by in situ anodic electrodeposition on the three-dimensional macroporous nickel foam (NF) substrate followed by heat treatment with H2. The as-prepared H-NiFeCuO/NF electrode showed the initial potential of 1.44 V (versus RHE) for OER and 980 F g−1 specific capacity as supercapacitor in 1 M KOH. Further investigation suggested that the tuning of composition and structure by doping copper ions and creating OVs helped accelerate the electrochemical reactions. This practice provides an efficient approach for the fabrication of heteromultimetallic hydroxide monolithic electrode with high performance in OER or supercapacitor application.

Fe/Fe3C@CNTs anchored on carbonized wood as both self-standing anode and cathode for synergistic electro-Fenton oxidation and sequestration of As(III)

Considering the hypertoxicity and poor affinity of arsenite toward sorbent materials, development and construction of effective purification technologies are of vital importance for efficient conversion of As(III) to As(V) and concomitant capture of As(V). Herein, an electrochemical integrated system for As(III) removal is developed using 3D hierarchically porous hybrid monolith electrodes, constructed by Fe/Fe3C nanoparticles (NPs) and clusters encapsulated in N,O-codoped carbon nanotubes (CNTs) anchored on carbonized wood (CW) framework (denoted as Fe/Fe3C@CNTs/CW). Remarkably, the heterogeneous electro-Fenton reaction on the cathode promotes the oxidation of As(III) into As(V); while the electro-sorption on the anode is conducive to the subsequent arsenic immobilization. Under the optimized conditions, trace As(III) species (1 ppm) can be efficiently removed within 90 min, in which the residual arsenic concentration is below the threshold value (10 ppb) in the drinking water recommended by the World Health Organization (WHO). Significantly, the saturation electro-sorption capacity of the anode materials is approximately 10 times higher than that of physicochemical adsorption. The developed Fe/Fe3C@CNTs/CW electrode exhibits not only superior structural stability due to the protective action from the carbon chainmail but also satisfactory recycling capability with negligible decay in removal efficiency after five cycles, signifying its huge potential in the future sustainable remediation application.

Monolithic Co-N-C membrane integrating Co atoms and clusters as a self-supporting multi-functional electrode for solid-state zinc–air batteries and self-powered water splitting

For practical applications in electrochemical devices such as zinc air batteries and alkaline water electrolyzers, an efficient electrode design with satisfactory multifunctional catalytic activity is a pivotal prerequisite. Herein, a self-supporting monolithic electrode for electrocatalyst-based devices with exceptionally high multi-functional catalytic activity is presented. The optimized tri-functional activity is recorded at a current density of 10 mA cm−2 with an overpotential at 36 mV for HER, and 229 mV for OER, indicating 1.51 V in an alkaline water electrolyzer, as well as a half-wave potential of 0.858 V for ORR. More importantly, the catalyst electrode exhibits an extremely low charge–discharge potential gap (ΔE less than 0.5 V) in solid-state rechargeable zinc-air batteries, attributed to its monolithic characteristics. Consequently, a self-powered hydrogen production system is driven by the identical pieces of the CoNC monoliths and zinc foil as a power source.

Constructing a hierarchically structured KNi0.67Co0.33PO4·H2O-graphene hydrogel/Ni foam electrode for superior all-solid-state supercapacitor.

A monolithic supercapacitor electrode of a KNi0.67Co0.33PO4·H2O-graphene composite hydrogel supported on Ni foam (KNCP-GH/NF) is first prepared by a one-step hydrothermal method, which achieves notable improvements in the electrode surface area and mass-loading of active materials. The KNCP-GH/NF electrode enjoys a hierarchical open-porous structure, where the KNCP-GH composite hydrogel fills in the voids in NF and the porous graphene hydrogel (GH) simultaneously provides a large support surface for growing active KNCP nanoflowers. Accordingly, the KNCP-GH/NF electrode exhibits a strikingly high capacity of 3240 mC cm-2 (876 C g-1) at 2 mA cm-2 and a satisfactory rate performance with 78.3% retention at 100 mA cm-2. Further, an all-solid-state asymmetric supercapacitor, constituted by using KNCP-GH/NF and Fe2P/GH/NF as the cathode and anode, respectively, and PVA-KOH as the solid-state gel electrolyte, delivers a high energy density of 69.2 W h kg-1 (3.9 mW h cm-3) and a power density of 13 229 W kg-1 (720 mW h cm-3) as well as notable cyclability with 81.2% capacity retention after 10 000 charge/discharge cycles. These attractive performances suggest a promising potential for a hierarchically structured KNCP-GH/NF electrode for the high-performance energy storage application.

3D graphene nanosheets from plastic waste for highly efficient HTM free perovskite solar cells.

Herein, we report the first time application of waste plastic derived 3D graphene nanosheets (GNs) for hole transport material (HTM) free perovskite solar cells (PSCs), where 3D GNs have been employed as an electrode dopant material in monolithic carbon electrode based mesoscopic PSCs. Waste plastics were upcycled into high-quality 3D GNs by using two-step pyrolysis processes, where, a nickel (99.99%) metal mesh was taken as the catalytic and degradation template to get an acid free route for the synthesis of 3D GNs. Raman spectroscopy, HRTEM analysis and XRD analysis show the presence of 1–2 graphene layers within the 3D GNs. Further, the optical band gap study has also been performed to analyze the applicability of 3D GNs for PSCs. The optimized device with 3D GNs shows a power conversion efficiency (PCE) of 12.40%, whereas the carbon-based control device shows a PCE of 11.04%. Further, all other device parameters such as short circuit current (Jsc), open circuit voltage (Voc) and fill factor (FF) have been improved with the addition of 3D GNs. The performance enhancement in 3D GN doped HTM free PSC solar cells is attributed to the enhancement in conductivity and reduced recombination within the device. Further, the photocurrent study shows that the 3D GN device shows better performance as compared to the reference device due to the larger diffusion current. Thus, the upcycling of waste plastics into 3D GNs and their exploitation for application in energy conversion show an effective and potential way to convert waste into energy.

Electrochemical properties of an activated carbon xerogel monolith from resorcinol-formaldehyde for supercapacitor electrode applications.

Activated carbon xerogel monoliths were prepared from resorcinol and formaldehyde via a catalyst-free and template-free hydrothermal polycondensation reaction, followed by pyrolysis and activation. The ratio of resorcinol (R) to distilled water (W) was varied to afford an interconnected pore structure with controlled pore size, while the pyrolysis temperature was optimized to give high specific surface area. Activation was carried out at 700 °C after soaking the samples in 6 M KOH aqueous solution. The same process, called “heat treatment”, was also carried out without soaking in KOH for comparison. The weight loss upon pyrolysis, activation and heat treatment and the weight gain via KOH soaking were measured. Field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and an N2 sorption instrument were utilized for characterization. Additionally, electrochemical properties were evaluated using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS) with a 3-electrode system, while a 2-electrode system was also employed for selected samples. The highest specific capacitance of 323 F g−1via GCD at 1 A g−1 was obtained at the R/W ratio of 45 and with 500 °C pyrolysis. In addition, this sample also exhibited 89.4% retention at 20 A g−1 in the current density variation and 100% retention in 5000 cycling tests.

Nanoporous Surface High‐Entropy Alloys as Highly Efficient Multisite Electrocatalysts for Nonacidic Hydrogen Evolution Reaction

AbstractElectrocatalytic hydrogen evolution in alkaline and neutral media offers the possibility of adopting platinum‐free electrocatalysts for large‐scale electrochemical production of pure hydrogen fuel, but most state‐of‐the‐art electrocatalytic materials based on nonprecious transition metals operate at high overpotentials. Here, a monolithic nanoporous multielemental CuAlNiMoFe electrode with electroactive high‐entropy CuNiMoFe surface is reported to hold great promise as cost‐effective electrocatalyst for hydrogen evolution reaction (HER) in alkaline and neutral media. By virtue of a surface high‐entropy alloy composed of dissimilar Cu, Ni, Mo, and Fe metals offering bifunctional electrocatalytic sites with enhanced kinetics for water dissociation and adsorption/desorption of reactive hydrogen intermediates, and hierarchical nanoporous Cu scaffold facilitating electron transfer/mass transport, the nanoporous CuAlNiMoFe electrode exhibits superior nonacidic HER electrocatalysis. It only takes overpotentials as low as ≈240 and ≈183 mV to reach current densities of ≈1840 and ≈100 mA cm−2 in 1 m KOH and pH 7 buffer electrolytes, respectively; ≈46‐ and ≈14‐fold higher than those of ternary CuAlNi electrode with bimetallic Cu–Ni surface alloy. The outstanding electrocatalytic properties make nonprecious multielemental alloys attractive candidates as high‐performance nonacidic HER electrocatalytic electrodes in water electrolysis.

Improving Flow-through Electrode Performance Using Computational Design of Architected Porosity

Electrochemical systems such as fuel cells, flow batteries, and electrochemical reactors are prevalent in industry, but few tools for their numerical design and optimization exist. Controlling fluid flow, active species distribution, and mass transport in the electrode has a dramatic impact on power and efficiency. However, this control is often limited to changing a quasi-two-dimensional flowfield and selecting bulk properties of a monolithic porous material electrode like carbon felt or paper. This can lead to non-uniform reaction rates, underutilized regions of the flow cell, and can limit the ultimate performance of the devices. To address these limitations, we propose using electrodes composed of a micro-architected variable porosity medium. As a specific example, we enable variable porosity by leveraging advances in the additive manufacture of microscale iso-truss lattices. We employ physics-based homogenization of the governing microscopic, continuum transport equations to develop a descriptive model and enable the design of this variable porosity electrode. Our tool is used to generate optimized architectures which are predicted to outperform monolithic electrodes when used in a standard flow-through configuration. We conclude by demonstrating how the optimal porosity distribution changes to retain the performance benefits as the electrode is scaled beyond benchtop-experimentsLLNL-ABS- 810799This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

(Invited) Three-Dimensional Nanostructuring of Metal-Organic Frameworks for Energy Applications

Metal-organic frameworks (MOFs) are a growing family of microporous materials that are attracting significant research and industrial interest, thanks to their unique features including a tuneable and narrow intrinsic pore size distribution, and very high surface area. MOFs are also being increasingly used as a precursor for the preparation of well-dispersed metal-containing carbon electrodes. A major challenge remains the three-dimensional structuring of MOFs into hierarchical functional morphologies and their integration as active elements in electrical material systems, due to their usually low electronic conductivities. Here, we present some flexible strategies for the structuring of MOFs into three-dimensional morphologies and their application for energy storage. In particular, we focus on lithium–sulfur (Li–S) batteries as a promising system for the next-generation of high energy density batteries. Despite progress, the energy density of current Li–S technologies is still below that of conventional intercalation-type cathode materials, due to limited stability and utilization efficiency at high sulfur loading.We demonstrate a highly performing free-standing monolithic electrode architecture for Li–S batteries with superior electrochemical stability and energy density [1]. The electrode layout consists of a highly conductive three-dimensional network of N,P co-doped carbon with well-dispersed metal-organic frameworks nano-domains of ZIF-67 and HKUST-1. The hierarchical monolithic 3D carbon networks provides an excellent environment for charge and electrolyte transport as well as mechanical and chemical stability. The electrically-integrated MOF nano-domains significantly enhance the sulfur loading and retention capabilities by inhibiting the release of lithium polysulfide specifies as well as improving the charge transfer efficiency at the electrolyte interface. Our optimal 3D carbon-HKUST-1 electrode architecture achieves a very high areal capacity of > 16 mAh cm−2 with a capacity retention of 82 % at 0.2C for over 300 cycles, providing an attractive candidate material for future high energy density Li–S batteries. We believe that our approaches provide some promising directions for the engineering of functional MOF morphologies for electrochemistry. References Liu, B.; Bo, R.; Taheri, M.; Di Bernardo, I.; Motta, N.; Chen, H.; Tsuzuki, T.; Yu, G.; Tricoli, A. Nano Lett. 2019, 19, (7), 4391-4399.

Increasing bioelectricity generation in microbial fuel cells by a high-performance cellulose-based membrane electrode assembly

Economically harvesting energy from a microbial fuel cell (MFC), increasing its electrical power production, and developing its role as a practical energy supply, needs a low-cost and high-performance design of the MFC compartments. According to this strategy, a novel monolithic membrane electrode assembly (MEA) was fabricated and evaluated as an air–cathode in a single-chamber MFC (SCMFC). The MEA was made of bacterial cellulose (BC), conductive multi-walled carbon nanotubes (CNT), and nano-zycosil (NZ). BC, as a nano-celluloses with oxygen barrier property, can maintain anaerobic conditions for the anode compartment. Binder-less CNT coating on BC avoids costly binders such as poly-tetra fluoro ethylene (PTFE) and Nafion and decreases the MEA charge transfer resistance. NZ, as a very cheap modifier, not only prevents the anolyte leakage but also provides more MEA’s active sites for the oxygen reduction reaction (ORR). The electrochemical performance of the MEA was compared to a PTFE- based gas diffusion electrode (GDE) in the SCMFC. The MEA cell provided a pulse power density of 1790 mW/m2, roughly twice as high as the pulse power density of GDE (920 mW/m2). SCMFC’s internal resistance decreased from 1.84 KΩ (with GDE) to 0.8 KΩ (with MEA). Also, the cell’s columbic efficiency increased from 4.2% (with GDE) to11.7% (with MEA). Additionally, the capacitance of the MEA (65 mF) was much higher than the value for GDE (0.73 mF). Thus, the MEA compared to the GDE showed higher performance in the SCMFC for electricity generation and wastewater treatment at a lower cost.