Interconnected Hierarchical Porous Structure Research Articles

Highly dispersed cobalt clusters/nanoparticles embedded in cellulose nanocrystal derived carbon aerogel as efficient sulfur host for high performance lithium sulfur batteries

Exploring multifunctional sulfur host materials with high immobilization ability and catalytic activity is of great significance for realizing high-performance Lithium-sulfur (Li–S) batteries. Recently, cellulose nanocrystals (CNCs) receive extensive attention for advanced energy storage applications owing to their intrinsically exceptional physical/chemical properties and natural abundance. Herein, a highly dispersed cobalt clusters/nanoparticles embedded into CNC derived carbon aerogel composite (CA/Co-2) is for the first time synthesized. Benefiting from the interconnected hierarchical porous structure, homogeneously anchored Co clusters/nanoparticles and N-doped species, the designed CA/Co-2 could enable rapid electron/ion transport, efficient sulfur utilization, effective suppression of the shuttle effect and fast catalytic conversion of polysulfides, thereby contributing to outstanding electrochemical performance. Consequently, CA/Co-2@S cathode delivers high initial discharge capacity (1553.1 mAh g−1 at 0.1C) and superior cycle stability. Moreover, a remarkable rate performance of 681.4 mAh g−1 at 5.0C and exceptional long-term cycling stability with an ultralow capacity decay of 0.028 % per cycle at 5.0C over 1000 cycles could be achieved when coupled with carbon paper interlayer. This work develops a workable strategy for fabricating multifunctional sulfur host derived from the fascinating bio-nanomaterial of CNC, which provides valuable guidance for the future design of high-performance Li–S batteries.

Hierarchically interconnected WS2/graphene foam for high-performance sodium storage

Sodium-ion batteries (SIBs), as the promising energy storage systems alternative to lithium-ion batteries (LIBs), are given increasing expectations and highly valued owing to the abundant reserves and low cost of sodium-containing minerals. However, further applications are still limited by the lack of anode material with high capacity and long cycle life. Herein, highly permeable foam-like tungsten disulfide/reduced graphene oxide composites with 3D interconnected hierarchical porous structure (3DHP WS2/RGO) are designed and studied as anode materials in SIBs. Remarkably improved battery performance is obtained, including high reversible capacity (419 mA h g−1 at 100 mA g−1), excellent cycling stability (1000 cycles) and superior rate capability (360 mA h g−1 at 2 A g−1). Electrochemical characterizations reveal that the high pseudocapacitive behavior dominates the fast ions/charge reaction kinetics, and the reversible conversion between Na2S generated in the first discharge process and S as evidenced by various advanced characterization techniques dominates sodium storage. The exceptional performance exhibited by 3DHP WS2/RGO composite sheds new light on the development of two-dimensional transition metal dichalcogenides-based materials for next-generation energy storage systems.

In situ growth of surface-reconstructed aluminum fluoride nanoparticles on N, F codoped hierarchical porous carbon nanofibers as efficient ORR/OER bifunctional electrocatalysts for rechargeable zinc-air batteries

Modified porous carbon fibers have emerged as crucial electrocatalytic materials for zinc-air battery (ZAB) systems. However, most methods for preparing porous carbon fibers are complex and exhibit single functionality and poor catalytic activity, which hinders the development of ZABs. In this study, we design and synthesize a novel type of N, F codoped hierarchical porous carbon fiber with in situ growth of aluminum fluoride nanoparticles (AlF3@HPCNFs) through electrospinning and high-temperature carbonization. The N, F codoping effectively adjusts the charge density of neighboring carbon atoms and introduces additional active sites. Furthermore, the catalytic process induces surface reconstruction of AlF3 nanoparticles, allowing for their full exposure to the liquid electrolyte and accelerated catalytic reactions. Additionally, this interconnected hierarchical porous structure accelerates mass transfer at the oxygen/carbon-based substrate/electrolyte three-phase interfaces, thereby enhancing reaction kinetics and the accessibility of catalytic active sites, ultimately improving the utilization efficiency of these sites. Consequently, the AlF3@HPCNFs catalyst exhibits excellent bifunctional performance with a narrow potential difference (△E = 0.67 V). Moreover, the obtained bifunctional electrocatalyst is utilized for rechargeable ZABs, surpassing commercially available Pt/C + RuO2 cells in terms of high specific capacity (796 mAh gzn−1) and outstanding cycling stability (over 500 h). This research demonstrates the potential of AlF3@HPCNFs as a bifunctional electrocatalyst and introduces a simplified and effective method for the fabrication of metal fluoride-modified and hierarchically porous carbon nanofibers for rechargeable ZABs.

Flexible multi-layered porous CuxO/NiO (x = 1, 2) photo-assisted electrodes for hybrid supercapacitors: Design and mechanism insight

With the utilization of sustainable sunlight efficiently, it is of paramount important to develop a new type of electrode for boosting photo-assisted supercapacitor performance. Herein, this work originally designs the Ni35Cu15Zr15Ti35 metallic glass (MG) ribbon as dealloying precursor. Benefiting from the different oxidation behavior of Ni and Cu metals during the dealloying and anodizing processes, a new type of multi-layered porous hybrid photoelectrode (namely CuxO/np-NiCu@NiCuO/MG, x = 1, 2) that simultaneously achieve the flexible, hierarchical porous structure as well as the NiO/Cu2O heterojunction, are successfully synthesized. An intriguing multi-layered structure consists of the outermost photosensitive CuxO nanowire layer formed by the anodizing technique, the nanoporous NiCu@NiCuO layer just beneath the nanowire layer via the dealloying as well as the glass central layer offering an excellent flexibility. In particular, 3D interconnected hierarchical porous structure is benefit to the penetration and utilization of visible light efficiently. The photoelectrode demonstrates a maximum specific capacitance of 1182.2 F cm−3 with light irradiation, which is 18% higher than that without light. This photo-assisting charging for the supercapacitor is ascribed to the combination of photosensitive CuxO and pseudocapacitive NiO components. Moreover, the photoelectrode exhibits an excellent flexibility and the photocurrent response is basically unchanged after bending for 1000 times. The aqueous supercapacitor shows a maximum energy density of 44.9 mWh cm−3 under light. This work provides new insights into the development of next generation wearable photo-assisted supercapacitor.

Green synthesized carbon aerogel for electric double layer capacitor

As new-generation biomass-derived carbon materials, carbon aerogels offer opportunities in supercapacitor applications. Owing to their excellent properties viz., a synergy of unique interconnected hierarchical porous structure, high specific surface area (SSA), and electrical conductivity they prove their candidature in electric double layer capacitors (EDLCs). In this article, we represent a green synthesis of carbon aerogel using sugarcane juice as a carbon source via cost effective hydrothermal method instead of the traditional supercritical drying method which is more toxic, time-consuming, and expensive. The structural and compositional studies confirm the formation of Sugar Aerogel (SA). Additionally, the surface analysis shows the interconnected porous scoop-like structure with a high SSA of 2028 m2/g and a low bulk density of 0.08 g/cc. Furthermore, the synthesized powder was screen printed on flexible stainless-steel mesh to conduct electrochemical study at various Na2SO4 electrolyte concentrations (0.3, 0.6, 1.0, 2.0, 3.0 M). In 1.0 M Na2SO4 electrolyte, the SA showed 70% retention rate after 5500 cycles at 30 mA/cm2 current density over 1.9V potential window and also provides high energy density and power density 61.72 Wh/kg and 1588.33 W/kg respectively. Also, the SA||SA device exhibits stability over 1000 cycles with a 30% increment in capacitance with energy and power density 86 Wh/kg and 7920 W/kg. This study signifies the great potential of sugarcane juice to get SA via a simple, cost-effective, and environmentally friendly hydrothermal route for the fabrication of SC electrodes in neutral electrolyte Na2SO4.

Pickering Emulsion Templated 3D Cylindrical Open Porous Aerogel for Highly Efficient Solar Steam Generation.

Porous-structured evaporators have been fabricated for achieving a high clean water throughput due to their maximized surface area. However, most of the evaporation surfaces in the porous structure are not active because of the trapped vapor in pores. Herein, a three-dimensional (3D) cylindrical aerogel-based photothermal evaporator with a disordered interconnected hierarchical porous structure is developed via a Pickering emulsion-involved polymerization method. The obtained cotton cellulose/aramid nanofibers/polypyrrole (CAP) aerogel-based evaporator achieved all-cold evaporation under 1.0 sun irradiation, which not only completely eliminated energy loss via radiation, convection, and conduction, but also harvested massive extra energy from the surrounding environment and bulk water, thus significantly increasing the total energy input for vapor generation to deliver an extremely high evaporation rate of 5.368kg m-2 h-1 . In addition, with the external convective flow, solar steam generation over the evaporator can be dramatically enhanced due to fast vapor diffusion out of its unique opened porous structure, realizing an ultrahigh evaporation rate of 18.539kg m-2 h-1 under 1.0 sun and 4.0 m s-1 . Moreover, this evaporator can continuously operate with concentrated salt solution (20 wt.% NaCl). This work advances rational design and construction of solar evaporator to promote the application of solar evaporation technology in freshwater production.

Sustainable Lignin‐Derived Carbon as Capacity‐Kinetics Matched Cathode and Anode towards 4.5 V High‐Performance Lithium‐Ion Capacitors

The Li‐ion capacitors (LICs) develop rapidly due to their double‐high features of high‐energy density and high‐power density. However, the relative low capacity of cathode and sluggish kinetics of anode seriously impede the development of LICs. Herein, the precisely pore‐engineered and heteroatom‐tailored defective hierarchical porous carbons (DHPCs) as large‐capacity cathode and high‐rate anode to construct high‐performance dual‐carbon LICs have been developed. The DHPCs are prepared based on triple‐activation mechanisms by direct pyrolysis of sustainable lignin with urea to generate the interconnected hierarchical porous structure and plentiful heteroatom‐induced defects. Benefiting from these advanced merits, DHPCs show the well‐matched high capacity and fast kinetics of both cathode and anode, exhibiting large capacities, superior rate capability and long‐term lifespan. Both experimental and computational results demonstrate the strong synergistic effect of pore and dopants for Li storage. Consequently, the assembled dual‐carbon LIC exhibits high voltage of 4.5 V, high‐energy density of 208 Wh kg−1, ultrahigh power density of 53.4 kW kg−1 and almost zero‐decrement cycling lifetime. Impressively, the full device with high mass loading of 9.4 mg cm−2 on cathode still outputs high‐energy density of 187 Wh kg−1, demonstrative of their potential as electrode materials for high‐performance electrochemical devices.

Ultrahigh Content Boron and Nitrogen Codoped Hierarchically Porous Carbon Obtained from Biomass Byproduct Okara for Capacitive Deionization.

Capacitive deionization (CDI) is an environmentally friendly, energy efficient, and low cost water purification technique in comparison with other conventional techniques, and it has attracted considerable attention in recent years. Here, we use biomass byproduct okara as the starting material to fabricate a boron and nitrogen codoped hierarchically porous carbon (BNC) with ultrahigh heteroatom contents and abundant in-plane nanoholes for CDI application. With the interconnected hierarchical porous structure, the BNC not only exhibits a large surface area (647.0 m3 g-1) for the adsorption of ions but also offers abundant ion transport channels to access the entire internal surface. Meanwhile, the ultrahigh dopants' content of B (11.9 at%) and N (14.8 at%) further gives rise to the increased surface polarity and enhanced capacitance for BNC. Owing to these favorable properties, BNC exhibits top-level salt adsorption capacity (21.5 mg g-1) and charge efficiency (59.5%) at the initial NaCl concentration of ∼500 mg L-1. Moreover, we performed first-principle simulations to explore the different effects between N-doping and N,B-codoping on the capacitive property, which indicate that the boron and nitrogen codoping of carbon can largely increase the quantum capacitance over the double layer capacitance. The results of this work suggest a promising prospect for the BNC material in practical CDI application.

Nitrogen-doped hierarchical porous carbon obtained from silk cocoon for capacitive deionization

Capacitive deionization (CDI) has recently emerged as an alternative technology for water desalination. In this work, N-doped hierarchically porous carbon (NPC) has been synthesized using a sustainable and facile silk cocoon for its use as a high-performance CDI electrode. With an interconnected hierarchical porous structure, the NPC not only offers highly efficient ion transport pathways, but also provides a sufficient specific surface area (1315 m2·g−1) for the storage and adsorption of the ions. As a result, the NPC electrode affords a remarkable specific capacitance of 137.0 F·g−1 in 1.0 M NaCl solution, and enables an outstanding electrosorption capacity of 7.0 and 32.8 mg·g−1 with an initial NaCl concentration of 50.0 and 2500.0 mg·L−1, respectively. While, it also shows a high charge efficiency, salt adsorption rate, and cycle stability. The effectively N-doping and partly graphitizing of carbon in this porous material were regarded as the main reasons account for the satisfactory salt removing property. This study reveals that the NPC material exhibits a promising prospect for practical CDI application.

Direct ink writing of porous SiC ceramics with geopolymer as binder

We herein report a novel strategy for direct ink writing of porous SiC parts by using geopolymers (GP) as binders and sintering SiC/GP composites at high temperatures via carbothermal reduction. The effects of treatment temperatures on the microstructure, pore size distribution and compressive strength of SiC/GP composites were systematically investigated. The total porosity of porous SiC carriers was as high as 76.4 vol% after being sintered at 1800 °C and exhibited a much broader pore size distribution (pore volumes) between 39 nm and 13.951 µm (~1.68 mL/g) accompanied by an interconnected hierarchical porous structure. After loading lamellar graphene oxide into the porous SiC carrier to form GO/SiC adsorbents, they exhibited fast and near-unity removal of methylene blue, and the adsorption efficiency still exceeded 82.0% after multiple times usage. These results prove that it is possible to remove hazardous materials from wastewater using reusable porous SiC ceramics as reusable adsorbent carriers.

Controllable synthesis of hierarchical nanoporous carbon@Ni(OH)2 rambutan-like composite microspheres for high-performance hybrid supercapacitor

Design of electrode materials with excellent electrochemical properties for advanced energy storage device are important to the sustainable development of energy resources. In this manuscript, a novel hierarchical nanoporous [email protected] hydroxide ([email protected](OH)2) composites were prepared through simple in-situ chemical deposition of Ni(OH)2 nanocrystals on HNCMs. By tailoring the deposition amount, core–shell structured rambutan-like [email protected](OH)2 microspheres with hairy nickel hydroxide nanocrystal covered on HNCMs were obtained. Ascribed to the high specific capacitance of nickel hydroxide and the interconnected hierarchical porous structure of HNCMs, the resultant rambutan-like [email protected](OH)2 microspheres as electrode materials display outstanding electrochemical properties including high specific capacity of 248.9 mAh/g at 1 A/g and good capacitance retention of 62.9% at 20 A/g. Furthermore, a hybrid supercapacitor with rambutan-like [email protected](OH)2 microspheres as cathode and HNCMs as anode were assembled and showed a comparable energy density of 41.3 Wh/kg at the power density of 173.3 W/kg and high capacity retention of 85.2% after 20,000 cycles at 5 A/g. As a proof of concept example, the fabricated hybrid supercapacitor can be utilized as energy source to instantaneous light up a red LED indicator. We envisioned that the as-prepared rambutan-like [email protected](OH)2 microspheres have great potential in constructing of advanced energy storage devices.

Microalgae hydrogel-derived monolithicfree-standing air cathode for microbial fuel cells: Tailoring the macroporous structure for enhanced bioelectricity generation

A high-performance and cost-effective cathode is highly desirable for the practical implementation of microbial fuel cell (MFC) technology, used for renewable energy recovery from wastewater. In this study, a monolithic, free-standing air cathode for MFCs is fabricated through a sol-gel-based route. Chlorella pyrenoidosa (CP) is selected as the catalyst precursor, polyacrylonitrile fiber as the precursor for the conductive and supporting skeleton, and deionized water as the solvent and pore former. Agar is also used as the gelling agent to facilitate the formation of 3D porous networks inside the cathodes. By systematically tailoring the porosity of the tubular air cathodes by varying the water content in the CP agar composite hydrogel, the mechanical strength and electrical conductivity of the cathode is optimized. Moreover, this fabrication process leads to abundant active sites for the oxygen reduction reaction and an interconnected hierarchical porous structure with separated transport paths for air supply and ion transfer. The tubular air cathode can be directly employed as an MFC cathode without the use of a polymer binder or other modifications. The MFC delivers a maximum power density of 106.3 ± 5.9 W m-3, which is approximately 33% higher than that with a converntional Pt/C cathode (79.8 ± 4.1 W m-3). This work therefore offers a promising new route for recovering bioelectricity from wastewater based on MFCs.

Self-Healing Hydrophilic Porous Photothermal Membranes for Durable and Highly Efficient Solar-Driven Interfacial Water Evaporation

Self-Healing Hydrophilic Porous Photothermal Membranes for Durable and Highly Efficient Solar-Driven Interfacial Water Evaporation

Novel composite nano-materials with 3D multilayer-graphene structures from biomass-based activated-carbon for ultrahigh Li-ion battery performance

Graphene composite materials have attracted significant attention for green energy storage systems due to their excellent electrochemical properties. We report a low-cost and environmentally friendly approach for synthesis of 3D multilayer graphene nanostructures (3DMGS) via catalytic graphitization and chemical oxidation-thermal reduction using biomass-based activated carbon (AC) as a precursor. The combination of microwave catalytic graphitization and chemical oxidation results in an active material with a unique physical and chemical structure. 3DMGS possesses a high specific surface area (503 m2 g−1) and an interconnected hierarchical porous structure with many defects and edges, which provide sufficient lithium-ion diffusion sites and facilitate fast ion transportation. When used as anode material for Li-ion batteries, 3DMGS exhibit outstanding rate capability and cycling stability (260 mAhg−1 at 5000 mAg−1 after 1100 cycles with charge retention of 114.47%.) and ultrahigh specific capacity (1513 mAhg−1 at 100 mAg−1).

Superior stability and methanol tolerance of a metal-free nitrogen-doped hierarchical porous carbon electrocatalyst derived from textile waste

Heteroatom-doped carbon materials with hierarchical porous structures are promising alternatives to replace the use of scarce platinum catalysts in fuel cells for oxygen reduction reaction (ORR). In this work, nitrogen-doped hierarchical porous carbon is developed from abundantly available textile waste activated with calcium chloride as the pore forming agent and inexpensive urea as the nitrogen precursor followed by pyrolysis. The obtained porous carbon, namely TCPB, has a 3D interconnected hierarchical porous structure (sponge-like) with high surface area (495.97 m2 g−1) and good nitrogen doping (2.80 at%). TCPB exhibits excellent ORR activity (E0 = 0.948 V vs RHE) via the 4-electron transfer pathway with low H2O2 production (6.9–8.91%), superior stability (negligible performance loss) and good tolerance to 3 M methanol when compared to commercial Pt in alkaline media. These results indicate the conversion of textile waste with simple synthesis steps able to produce nitrogen doped porous carbon catalyst with excellent performance thus offering great advantage for fuel cell application.

Honeycomb-like nitrogen-superdoped porous carbon for high performance supercapacitors

Honeycomb-like nitrogen-doped porous carbon (HNC) is prepared by using poly(2,6-diaminopyridine) as nitrogen-enriched precursor and silica as hard template. After carbonization and template removal, the obtained HNC possesses an interconnected 3D hierarchical porous structure and a nitrogen level up to 15.31 at.%. Owing to the hierarchical porous structure and abundant active sites in the carbon matrix, the HNC exhibits an excellent capacitive performance with a high specific capacitance of 398 F g−1 at a current density of 0.1 A g−1 and exceptional cycling stability (110.4% retention after 5000 cycles). This work provides a facile and efficient strategy for the large-scale production of nitrogen superdoped interconnected hierarchical carbon framework for high performance supercapacitors.

Highly sensitive detection of gallic acid based on 3D interconnected porous carbon nanotubes/carbon nanosheets modified glassy carbon electrode

Carbon materials have great significance to improve the detection performance of electrochemical sensors. It is still a great challenge to prepare the carbon-based gallic acid (GA) electrochemical sensor with excellent detection performance based on a simple, economical and scalable synthetic strategy. In this work, we fabricated a highly sensitive GA electrochemical sensor by modifying the glassy carbon electrode (GCE) with a hybrid carbon composite of 3D interconnected porous carbon nanotubes/carbon nanosheets (3D IPCNT/CNS) for the first time. The hybrid carbon composite was prepared via a scalable ball-milling strategy followed by thermal decomposition. The whole synthesis process did not involve the use of template and complex morphology control process. In this hybrid carbon material, carbon nanotubes and carbon nanosheets were integrated into a 3D interconnected hierarchical porous structure, which served as a conductive network with large specific surface area and surface functional groups. These advantages provided sufficient electrolyte-electrode interface, facilitated the electron transport, and enhanced the surface affinity for GA at the interface between the modified electrode and electrolyte. The fabricated 3D IPCNT/CNS/GCE sensor showed satisfactory linear relationship between peak current and GA concentration in the broad range of 0.05−20 μM with relatively low detection limit of 0.016 μM and limit of quantification of 0.053 μM (S/N=3). Moreover, the fabricated sensor exhibited good reproducibility, high stability, and excellent selectivity. A satisfactory GA recovery and detection in green tea as well as black tea suggested practical application possibility of the 3D IPCNT/CNS/GCE sensor for highly sensitive determination of GA.

Fe3C/Fe, N-codoped porous carbon from petroleum vacuum residual for highly efficient oxygen reduction

The development of earth-abundant electrocatalysts to replace noble metal for oxygen reduction reaction (ORR) has attracts tremendous interest. In this work, Fe, N-codoped porous carbon-embedded Fe3C nanoparticles (Fe3C/Fe, N-PCR) is fabricated from petroleum vacuum residue via a simple template-assisted and subsequent doping-assisted calcination method. The unique hybrid material shows great features: abundant active sites including pyridinic N, FeN, and Fe3C nanoparticles, a relatively large surface area (509.3 m2 g−1) and 3D interconnected hierarchical porous structure. The Fe3C/Fe, N-PCR as an electrocatalyst exhibits remarkable ORR catalytic activity in alkaline medium, with a high onset potential of 1.02 V and half-wave potential of 0.86 V, which surpass commercial Pt/C (20 wt%) by ca. 30 and 20 mV, respectively. Moreover, Fe3C/Fe, N-PCR has outstanding long-term stability and tolerance to methanol poisoning, outperforming Pt/C. Combining with the exciting performance, abundant and cheap raw material, and facile synthetic method, Fe3C/Fe, N-PCR catalyst has promising future in ORR. This study also provides a new approach for high value utilization of petroleum vacuum residue.

Hierarchical porous carbon derived from wood tar using crab as the template: Performance on supercapacitor

Owing to intrinsic structural limitations, it is difficult to control the pore structure of biomass to synthesize hierarchical porous carbons (HPCs) to achieve high supercapacitor performance. As an inevitable by-product of the thermochemical conversion of biomass, wood tar exhibits good thermoplasticity and high-carbon content, and can be used as an alternative carbon source for biomass to prepare HPCs. To improve the utilization of wood tar, a facile synthetic route is proposed for preparing HPCs, based on a natural biological template method coupled with KOH activation. The HPCs possess favorable features in terms of high solid-carbon yield, high oxygen content (~9 at%), large specific surface areas (626.43–2489.62 m2 g−1), and an interconnected hierarchical porous structure, which greatly improved wettability and synergistically enable the construction of high-performance supercapacitors in aqueous and organic systems. The optimized HPC electrode exhibits a specific capacitance of 338.5 F g−1 in a 6 M KOH electrolyte, and the constructed symmetric supercapacitors deliver high energy densities up to 9.9 Wh kg−1 and 33.87 Wh kg−1 in aqueous and organic electrolytes, respectively. This study provides an effective route for the utilization of wood tar and crab shell waste.

One-Step Activation Synthesized Hierarchical Porous Carbon Spheres from Resorcinol–Thiourea–Formaldehyde for Electrochemical Capacitors

In this work, a facile one-step KOH activation strategy has been developed toward synthesis of N/S-codoped hierarchical porous carbon spheres (NSHPCSs) from resorcinol–thiourea–formaldehyde sphere precursors. Quite different from the samples prepared by a traditional two-step activation that includes a successive KOH activation after carbonization, NSHPCSs possess a typical interconnected hierarchical porous structure comprised of macro-, meso-, and micropores with large pore volume and suitable pore size distribution, together with heteroatom doping of N and S. Originating from the above synergetic effect, the resultant NSHPCSs deliver a high specific capacitance of 295 F/g at 0.5 A/g, outstanding rate capability (78.6% retention at 20 A/g), and excellent cycling stability (95.2% retention over 5000 cycles). Furthermore, a symmetric supercapacitor achieves a high energy density of 7.36 Wh/kg at a power density of 100 W/kg. Thus, our study demonstrates an effective and simple approach of producing high-performance supercapacitor electrode materials for energy storage.