Advanced Energy Storage Technologies Research Articles

Optimal ESS allocation in distribution network using accelerated generalised Benders decomposition

With the advancement of energy storage technologies, installing an energy storage system (ESS) in a distribution network has become a new solution to accommodate more and more distributed renewable generations. In this study, the optimal allocation of distributed ESSs is studied to maximise the benefit of the distribution system operator. The ESS allocation problem is divided into two stages: the mixed integer investment problem as the first stage and the optimal operation problems considering daily charging/discharging schedule of ESSs as the second stage. To tackle the uncertainties of distributed generation output and base load, typical days (scenarios) are firstly obtained by the clustering method and thereafter the operation problems include a number of scenarios, each with the corresponding possibility. Then each second stage problem is relaxed to a second-order cone programming model. To efficiently solve the whole problem considering multiple scenarios, the generalised Benders decomposition (GBD) algorithm is adopted, which is further accelerated by relaxing and rebinding integer constraints. Numerical experiments are conducted on a 17-bus test system to demonstrate the effectiveness of the proposed method. Additionally, comparisons between different algorithms are performed to verify the merits of the proposed acceleration method with respect to the original GBD and the branch-and-bound algorithm.

Lithium-Sulfur Batteries with a Vertical Co9S8 Hollow Nanowall Arrays-Modified Celgard Separator

Advanced energy-storage technologies are urgently needed to satisfy the energy demands of the society. Sulfur is an appealing candidate for high energy-density batteries, owing to its high theoretical capacity (1,675 mA h g-1), natural abundance, and low cost.1-3 However, the rapid capacity degradation, low Coulombic efficiency, and short cycle life originating from polysulfide dissolution and migration remain challenging for the practical application of lithium-sulfur (Li-S) batteries.4, 5 Our previous reports have demonstrated that configuring interlayers between the separator and the sulfur cathode is an effective and convenient strategy to alleviate the shuttle effect.6 However, most of those interlayers are fabricated by vacuum-filtration method, which makes those polar materials easily stack together and thus form a very thick interlayer. Therefore, on the one hand, the transport of lithium ions will be limited by the thick polar interlayers, which is not desirable for fast insertion/de-insertion of Li ions and high rate capacity. On the other hand, the stacked thick interlayers, as an inactive material, will decrease the overall cell energy density. To address such issues, we present here a novel Co9S8 nanowall array with vertical hollow naoarchitecture as an efficient barrier for lithium polysulfides (LiPS) in Li-S batteries.7 We present well-aligned, hollow Co9S8 arrays in-situ grown on a Celgard (Co9S8-Celgard) separator as an efficient polysulfide barrier for high-performance Li-S cells without any significant increase in the weight and volume (Fig. 1a). This novel concept/strategy of designing a multifunctional separator via in-situ grown polar and conductive materials (Co9S8 hollow arrays) on a commercial separator dramatically suppresses the shuttle effect of LiPSs and significantly improves the electrochemical performance of Li-S cells. Due to its well-designed structure, in-situ growth/transformation, and the polarity and high conductivity of Co9S8, the Li-S cell with the Co9S8-Celgard separator not only effectively blocks the LiPSs even with pure sulfur cathodes with a high sulfur loading (5.6 mg cm-2), but also delivers excellent specific capacity, outstanding rate capability, and remarkable cycling stability for an impressive number of 1,000 cycles (Fig. 1b - d). In essence, the novel design and in-situ growth of MOF-derived multifunctional Co9S8 layers are crucial to suppress the severe polysulfide diffusion and alleviate the shuttle effect of LiPSs. We believe that this approach would promote greatly the development of modified separators, particularly the design and synthesis of multifunctional separators. Fig. 1 (a) Schematic illustration of the synthesis process of Co9S8-Celgard. (b) Rate performances at various cycling rates with the Celgard, MOF-Celgard, and Co9S8-Celgard separators. (c) Cycling performances of Li-S cells with high sulfur-loading cathodes with Co9S8-Celgard separators. (d) Long-term cycling performances of the Li-S cells with the Co9S8-Celgard separators at 1C rate for 1,000 cycles. REFERENCES 1 J. He, Y. Chen, W. Lv, K. Wen, C. Xu, W. Zhang, Y. Li, W. Qin, W. He, ACS Nano 2016, 10, 10981. 2 J. He, L. Luo, Y. Chen, A. Manthiram, Adv. Mater. 2017, 29, 1702707. 3 F. Wu, J. T. Lee, N. Nitta, H. Kim, O. Borodin, G. Yushin, Adv. Mater. 2015, 27, 101. 4 G. Zhou, S. Pei, L. Li, D. Wang, S. Wang, K. Huang, L. Yin, F. Li, H. Cheng, Adv. Mater. 2014, 26, 625. 5 J. He, Y. Chen, P. Li, F. Fu, Z. Wang, W. Zhang, J. Mater. Chem. A 2015, 3, 18605. 6 Y. Su, A. Manthiram, Nat. Commun. 2012, 3, 1166. 7 J. He, Y. Chen, A. Manthiram, Energ. Environ. Sci. 2018, 11, 2560. Figure 1

Lithium-Sulfur Batteries with a 1T MoS2/Graphene As a Highly Efficient Electrocatalyst

Advanced energy-storage technologies are urgently needed to satisfy the energy demands of the society. Lithium-sulfur (Li-S) batteries are one of the most attractive candidates for next-generation energy-storage technology.1-3 However, it is extremely crucial to suppress the inherent “polysulfide shuttle” for the Li-S batteries to be viable.4, 5 Although electrocatalysis has been shown to enhance cell stability, further performance improvement of Li-S cells is seriously hindered due to a lack of understanding of the electrocatalysis mechanism on the sulfur redox process. Herein the electrocatalysis mechanism on the sulfur redox process is revealed based on both experimental and theoretical work.6 We present the synthesis of well-designed, freestanding, three-dimensional graphene/1T MoS2 (3DG/TM) heterostructures as a highly efficient electrocatalyst for lithium polysulfide (LiPS) conversion.7 The metallic 1T MoS2 nanosheets are hydrophilic with rich active sites and high electronic conductivity that is six orders of magnitude higher than that of 2H MoS2. The high electronic conductivity facilitates fast electron transfer, the hydrophilic property benefits ion diffusion, and the dense active sites ensure sufficient catalytic activity for LiPSs. The 3DG/TM heterostructures of our designed material can maximize the aspect ratio of active catalytic sites. The freestanding, porous morphology of the 3DG/TM material facilitates electrolyte accessibility, enabling better ion transport. Benefitting from these synergistic effects (Fig. 1a), the cells with 3DG/TM exhibit excellent specific capacity and outstanding cycling stability. Furthermore, the fundamental understanding for the enhanced catalytic activity in the MoS2-supported systems is revealed via experimental characterizations and theoretical calculation, which provide new insights and opportunities to develop advanced Li-S batteries with highly efficient electrocatalysts for LiPSs. Based on the deep understanding of the electrocatalysis of LiPSs conversion, the well-designed 3DG/TM heterostructures with rich electrocatalytically active sites ensure high catalytic activity and thus significantly improve the electrochemical performance of Li-S batteries. Even with a very high sulfur loading (10 mg cm-2), the S/3DG/TM cathode not only effectively mitigates the LiPS shuttling, but also delivers excellent specific capacity, outstanding rate capability, and pronounced cycling stability for an impressive number of 500 cycles (Fig. 1b). Fig. 1 (a) The conversion process of LiPSs on a graphene surface with 1T MoS2. The 3DG/TM heterostructures work as a highly efficient electrocatalyst for LiPSs conversion. (b) Long-term cycling cyclability of 3DG/TM with catholyte at 1C rate. REFERENCES 1 Y. Fu, C. Zu, A. Manthiram, J. Am. Chem. Soc. 2013, 135, 18044. 2 J. He, Y. Chen, A. Manthiram, Energ. Environ. Sci. 2018, 11, 2560. 3 J. He, Y. Chen, A. Manthiram, iScience 2018, 36. 4 G. Tan, R. Xu, Z. Xing, Y. Yuan, J. Lu, J. Wen, C. Liu, L. Ma, C. Zhan, Q. Liu, T. Wu, Z. Jian, R. Shahbazian-Yassar, Y. Ren, D. J. Miller, L. A. Curtiss, X. Ji, K. Amine, Nature Energy 2017, 2, 17090. 5 J. He, Y. Chen, W. Lv, K. Wen, C. Xu, W. Zhang, Y. Li, W. Qin, W. He, ACS Nano 2016, 10, 10981. 6 G. Babu, N. Masurkar, H. Al Salem, L. M. R. Arava, J. Am. Chem. Soc. 2016, 139, 171. 7 J. He, G. Hartmann, M. Lee, G. S. Hwang, Y. Chen, A. Manthiram, Energ. Environ. Sci. 2019 (10.1039/C8EE03252A). Figure 1

(Invited) Design and Application of Advanced Materials in Electrochemical Energy Storage Systems

Green, efficient energy storage and conversion systems are an important means of addressing global environmental and energy crisis. The current battery systems have been difficult to meet the increasing market demand due to their relatively low energy densities, therefore it is urgent to develop new energy storage technologies with high energy density and low cost. To this end, Professor Zhongwei Chen and his research group adhere to a bottom-up “material-electrode-battery-system” strategy to develop a variety of advanced energy storage technologies, including lithium-ion batteries, zinc-air batteries, fuel cells, for a wide range of energy storage applications. Through the rational material design and engineering, various high-performance electrodes with hierarchical micro- and nanostructures have been developed. Moreover, the electrode structures are controlled and optimized toward high recharge efficiency and energy density. Together, these innovate materials and electrode architectures practically allow industrial assembly and production of more efficient, affordable, and safer battery systems for clean and sustainable energy storage.

High Rate Li-Ion Batteries with Cation-Disordered Cathodes

Summary Cation disordering in electrode materials for Li-ion batteries is deemed as an undesired structural feature for achieving high electrochemical activity owing to sluggish Li diffusion in the structure. Therefore, extensive efforts have been made to develop electrode materials having a well cation-ordered structure. We report a new class of cation-disordered material that can achieve reasonable Li diffusion by controlling the way of the cation distribution rather than the degree of cation disordering itself. The fully cation-disordered LiFeSO4F, activated by changes in the synthesis temperature and the Li/Fe ratio, delivers a substantially improved electrochemical performance. It exhibits a superior rate capability up to 100 C (36-s discharge) with ∼ 60 mAh/g and excellent capacity retention for 2,500 cycles at 5 C charge/20 C discharge rate. These results extend the scope of electrode materials to include cation-disordered materials and provide new opportunities for designing them for high-performance Li-ion batteries.

Horizons Community Board Collection – Progress and Development in Advanced Energy Storage Technologies

A themed collection on progress and development in advance energy storage technologies, guest edited by Materials Horizons Community Board members Vipin Kumar and Kai Zhang.

Optimized Li storage performance of B, N doped graphyne as Li-ion battery anode materials

As the economy grows and the environment deteriorates, the renewable energy is urgently needed. The advanced energy storage technology in electronic equipment, electric vehicle, smart grid, etc. becomes more significant. For example, the rechargeable batteries, hydrogen storage media, supercapacitors, the new energy storage devices have received much attention today. The anodes of the lithium ion battery (LIB), as the main body of charging and discharging, should be most important. The ideal anode material for LIBs is required to possess a higher Li capacity and a lower volume expansion. Good reversibility and high Li capacity are balanced necessarily in the electrode material. The poor cycling performance of LIB is usually due to the severe volume expansion of anode in lithiation/delithiation process. In this paper, the Li storage performance of B and N doped graphyne is explored by using the density functional theory method. The Perdew-Burke-Ernzerhof functional of the generalized gradient approximation is chosen. The calculations indicate that the doping of B atoms can enhance the adsorption strength between the Li atom and the graphyne, which can greatly increase the Li storage capacity. The Li storage capacity of B doped graphyne can reach as high as 2061.62 mAh/g, which is 2.77 times that of pristine monolayer graphyne. Meanwhile, the B doping reduces the out-plane diffusion energy barrier of Li, but increases the in-plane diffusion energy barrier slightly by 0.1 eV. On the other hand, the doping of N atoms reduces the interaction between Li and graphyne, however, the Li capacity also increases to 1652.12 mAh/g because the number of the available Li adsorption sites increases. Moreover, the doping of N atoms greatly improves the diffusion performance of Li on graphyne. The in-plane diffusion energy barrier drops to 0.37 eV, and thus the charge-discharge performance of the N doping graphyne is well improved. Therefore, the doping of B and N atoms can remarkably improve the performance of graphyne as the LIB anodes. The remarkable performance of B and N doped graphdiyne shows that it will become a promising LIB anode in the future. The present research can provide a good theoretical basis and thus conduce to guiding the developing of good Li storage materials, and can also supply strong background for experimental researches.

ACHIEVING RESILIENCE AND SUSTAINABILITY THROUGH INNOVATIVE DESIGN FOR OIL SHALE PYROLYSIS PROCESS MODEL

Low international oil price, advance in renewable energy technology, development of energy storage technology and strict environmental regulations have presented encumbrance and opportunity for the current oil shale project development. Oil shale industry is at critical stage and facing challenges from competitive conventional energy, clean renewable energy and more strict environmental regulations. Through an innovative design of the oil shale pyrolysis process model by utilizing a developed new advanced technology, the oil shale project could improve its resilience and sustainability with excellent social and economic performance.This paper investigated the shale oil production process in terms of technology selection, utilization of resource, energy efficiency, oil yield, and mining to improve the resilience of oil shale project economic performance facing lower oil price. Innovative design options for the oil shale production process model were discussed from the following aspects: 1) itemized cost analysis and comparison of shale oil production technologies; 2) development of a new oil shale pyrolysis process model with combination of the existing vertical retort process (VRP) and horizontal rotary-kiln retort process (HRRP) technologies to improve the oil shale process economic gain; 3) discussion of innovative design options to improve the economic performance of the process by utilizing the current new advanced energy storage technology. Investigation of the applicability of the energy storage system (ESS) to the oil shale project was carried out with a sensitivity analysis of its cost-revenue.

N-doped porous transition metal-based carbon nanosheet networks as a multifunctional electrocatalyst for rechargeable zinc-air batteries.

The development of cost-effective and highly efficient multi-functional oxygen reduction reaction and oxygen evolution reaction catalysts has attracted much research attention due to their great potential applications in many advanced clean energy storage and conversion technologies. Herein, highly efficient N-doped three-dimensional porous Co-Co3O4/C nanosheet network materials have been developed as bifunctional electrocatalysts for rechargeable zinc-air batteries.

Monetary Value of a District’s Flexibility on the Spot- and Reserve Electricity Markets

In the future, advanced multi-energy systems are expected to handle an increasing share of fluctuating renewable energy generation through the management of multiple advanced energy conversion and storage technologies operating across different energy carriers. The market diffusion of such concepts of Local Energy Management—the management of energy supply, demand, and storage within a given geographical area—is expected to provoke a fundamental reorganization of the power generation sector. This work contributes to this topic by estimating the maximum potential economic value attained from using the flexibility of a district to take advantage of operating within multiple electricity markets at the same time. The study is based on the measured demand and production data of a newly built suburban residential district located in Central Switzerland. The actual configuration of the district and the resulting flexibility, as well as an extension with a battery storage system, is used to estimate the economic value of the flexibility. Then, an optimization algorithm manages flexible demand, production, and storage capacities in order to alternatively maximize the revenues/cost savings, self-sufficiency, or share of renewable resources of the district’s energy supply. In this vein, the impact of the way the system operates in the markets regarding the degradation of the battery is assessed and its pay-back-time is estimated. The analysis revealed a considerable profit potential associated with the district thermal and electricity storage flexibility, in particular, when operating on both the spot and reserve electricity markets. Firstly, it was shown that overall energy costs can be minimized through an optimal management of energy conversion and storage systems. Secondly, complementing the infrastructure with batteries and trading flexibility on the spot market would decrease costs by about 43%, while an additional 20% cost decrease could be captured by including trading on the reserve market. Thirdly, it has been shown that operation on the spot- and reserve market does not seem to degrade the battery more than solely operation on the spot market. However, when operating on the spot- and reserve markets, battery amortization would still take about 10 years.

Mussel-inspired codepositing interconnected polypyrrole nanohybrids onto cellulose nanofiber networks for fabricating flexible conductive biobased composites

The exploitation of an efficient strategy for preparing flexible green conductive composites with an interconnected filler network is of great scientific and technical interest. Herein, a high-performance interconnected cellulose nanofiber (CNF) template functionalized tannic acid (TA)/polypyrrole (PPy) nanohybrid network (TPy@CNF) is fabricated by a green mussel-inspired co-modification approach. The network offers high electrical conductivity to prepare flexible, plant-derived soy protein isolate (SPI) composites. The mussel-inspired interface design demonstrates versatile functions of a reactive adhesion layer to construct a multiple-bond-regulated interconnected TPy@CNF conductive polymer network architecture without the need for harsh conditions and toxic reagents. This well-defined conducting TA/PPy-encapsulated CNF network is of great benefit in achieving strong synergistic interactions by enhancing electrical conductivity, reducing junction contact resistance, and ensuring efficient load transfer during bending. When integrating 7.5 wt% TPy@CNF, the prepared SPI composites deliver significantly enhanced conductivity of 0.078 S m−1 along with superior mechanical robustness (improved tensile strength and toughness) and excellent structural stability. This interconnected network design strategy can provide a green yet feasible approach for elaborate construction of CNF/conducting polymers in advanced energy-storage technologies.

Testing Large-Scale Energy-Storage Systems: Novel Safety Evaluations Can Be Run in a Spacious, New Indoor Chamber Available in Japan

The National Institute of Technology and Evaluation (NITE) launched the National Laboratory for Advanced Energy Storage Technologies (NLAB) in April 2016 in Osaka, Japan. NLAB has a large chamber to test containers up to 53 ft in length under controlled thermal and wind velocity conditions. This chamber is the first such indoor facility in the world. Based on the results obtained from a number of tests, NLAB has remarkable advantages for evaluating the safety requirements of large-scale megawatt-class battery energy-storage systems (BESs). Figure 1 provides a glimpse of the entrance hallway of this test facility, and Figures 2 and 3 show overall views of the Osaka complex.

Review of wholesale markets and regulations for advanced energy storage services in the United States: Current status and path forward

Today, advanced energy storage technologies, particularly electrochemical batteries, represent an increasingly economic option for supporting the integration of renewable energy resources and providing the grid with greater operational flexibility. Crucially though, the large-scale deployment of these assets, and the development of successful business models to support them is heavily reliant on policy, regulation and market design. In this paper, we present a comprehensive review of the array of federal, ISO/RTO and state-level rules and regulations shaping today's energy storage deployment across the United States. We highlight the fragmented and heterogeneous nature of existing market participation models available for advanced energy storage across restructured power markets and emphasize the need for design changes to power markets at all timescales to allow for the more efficient integration of energy storage. We also reflect on how well FERC's recent Order 841 does in terms of providing a framework for the establishment of more fit-for-purpose market participation models for storage, something that will be key for today's evolving power sector as it becomes more dependent on intermittent renewable resources.

Record Alkali Metal Intercalation by Highly Charged Corannulene.

The need for advanced energy storage technologies demands the development of new functional materials. Novel carbon-rich and carbon-based materials of different structural topologies attract significant attention in this regard. Attractive systems include a unique class of bowl-shaped polycyclic aromatic hydrocarbons that map onto fullerene surfaces and are thus often referred to as fullerene fragments, buckybowls, or π-bowls. Importantly, carbon bowls are able to acquire multiple electrons in stepwise reduction reactions producing sets of successively reduced carbanions. The resulting negatively charged π-bowls exhibit unique supramolecular assembly and metal intercalation patterns that only recently have begun to be uncovered. First, we have resolved the long-standing mystery behind the supramolecular structure formed by a highly reduced fullerene fragment called corannulene (C20H104-) with multiple lithium ions, using X-ray crystallography coupled with NMR spectroscopy and theoretical calculations. This work provided a new paradigm for lithium ion intercalation between the curved carbon π-surfaces and facilitated understanding of the lithium ion storage mechanism in carbonaceous matrices. Next, we have initiated a new research direction, an investigation of the mixed alkali metal reduction reactions using bowl-shaped corannulene as a remarkable multielectron reservoir and unique ligand with open convex and concave π-surfaces. As a result, we have revealed the cooperative effect of lithium with heavier Group 1 metals in reduction and self-assembly processes of corannulene. Moreover, we have discovered a new class of organometallic supramolecules having heterometallic cores with high nuclearity and charge such as Li3M36+ and LiM56+ (M = K, Rb, and Cs) sandwiched between two tetrareduced corannulene decks. The resulting triple-decker supramolecular assemblies, fully characterized by X-ray diffraction and spectroscopic methods, were found to exhibit a record ability of the highly charged corannulene π-surfaces to be fully engaged in intercalation of multiple metal ions. Based on this unique ability, curved π-ligands with extended carbon frameworks are expected to show remarkable potential for alkali metal storage compared to flat polycyclic arenes. Notably, a previously unseen mode of internal lithium binding revealed in the heterobimetallic sandwiches is accompanied by unprecedented negative shifts (up to -25 ppm) in 7Li NMR spectra. Based on in-depth analysis of NMR data, augmented by DFT calculations, we have rationalized the observed experimental trends and proposed the mechanism of stepwise alkali metal substitution reactions. Furthermore, we have correlated the origin of the record 7Li NMR shifts with unique electronic structures of these novel supramolecular aggregates. Herein we present comprehensive analysis of unusual structural and electronic features of remarkable heterometallic self-assemblies formed by tetrareduced corannulene, using a wealth of our recent experimental and computational results. This work uncovers unique potential of highly negatively charged bowl-shaped π-ligands for new supramolecular chemistry and materials chemistry applications.

An Asymmetric Boron-Centered Ionic Additive Enables High-Energy Density Lithium-Ion Batteries

To cater for drastically growing demands for batteries with high energy density and long-term cycle life in transportation sector and large-scale energy storage systems, advancement of energy storage technologies is urgently required. Because ultimate energy density of batteries can be realized through developing high-capacity electrode materials, structural optimization of electrode materials that are capable of storing high energy has been intensively addressed. In this study, we demonstrate the significant roles of artificially constructed surface on high-capacity Li-rich cathodes preventing mechanical fracture of the cathode particles, mitigating the exposure of inner surface of the cathode toward electrolytes by intergranular cracking, and alleviating voltage decay of the cathode by phase transformation and vulnerable interface. Newly synthesized asymmetric boron-centered ionic additive with partially fluorinated malonate bonded to a central boron core is employed as a functional additive ensuring interfacial stability of high-capacity SGC anodes and Li-rich cathodes. The action of the protective surface layer created by asymmetric boron-centered ionic additive on intergranular cracking of Li-rich cathode particles synthesized via co-precipitation is explored using field emission scanning electron microscopy (FE-SEM). The unique feature of asymmetric boron-centered ionic additive -induced interfacial structure scavenging the oxygen species derived by Li2MnO3 and mitigating undesirable phase transformation of Li-rich cathodes are elucidated through in situ differential electrochemical mass spectrometry (DEMS) and high-resolution transmission electron microscopy (HR-TEM) analyses, respectively. Furthermore, we examine the chemistry of the surface of both electrodes evolved by asymmetric boron-centered ionic additive using ex situ X-ray photoelectron spectroscopy (XPS) and demonstrate the possible mechanisms of asymmetric boron-centered ionic additive constructing stable electrolyte-electrode interface.

Hierarchical Carbon-Silicon Nanowire Heterostructures for Hydrogen Evolution Reaction

Silicon nanowires (SiNWs) opened up exciting possibilities in a variety of research fields due to their unique anisotropic morphologies, facile tuning capabilities, and accessible fabrication methods. The SiNW-based photoelectrochemical (PEC) conversion has recently been known to provide an efficiency superior to various photo-responsive semiconductor heterostructures. However, a challenge still remains in designing optimum structures to minimize photo-oxidation and photo-corrosion of Si surface in a liquid electrolyte. Here, we synthesized hierarchically branched carbon nanowires (CNWs) on SiNWs utilizing copper vapors as catalysts in a chemical vapor deposition (CVD) process, which exhibit outperforming photocatalytic activities for hydrogen generation along with excellent chemical stability against oxidation and corrosion. First, SiNWs were prepared by a metal catalyzed electroless etching method and placed at the center of a quartz reactor in a CVD chamber. Next, a Cu foil was placed above the SiNWs without a physical contact, where Cu vapors from the foil catalyzes the growth of CNWs on SiNWs while flowing 50 sccm H2 and 15 sccm CH­4 for 10~40 min at 1,000 ˚C in an ambient pressure. Scanning Electron Microscopy (SEM), Transmission electron microscopy (TEM), Selected Area Electron Diffraction (SAED), Raman spectroscopy, X-ray Photoemission Spectroscopy (XPS) analysis were employed to characterize the CNWs on the SiNWs, indicating that CNWs with various shapes and diameters are successfully grown on a SiNW. The PEC performance for the hydrogen evolution reaction shows that the catalytic activity is substantially dependent on the surface morphology of the CNWs-SiNWs. The applied bias photon-to-current efficiency (ABPE) in the optimized CNWs-SiNWs structure (1.86%) exhibits a higher value than in any of the other steps, which is also comparable to other carbon-based catalysts on the Si photocathode reported to date. Enhanced photocatalytic performance is substantially affected by the intrinsic wettability of the surface due to the polarization of electrochemical reaction. The long-term stability of the CNWs-SiNWs photocathode was tested for 300 cycles or for 11 hrs at a pH 0, showing a stable current density. The PEC performance of the Si cell is known to degrade easily due to surface oxidation in aqueous solutions, but our stability testing result implies that the CNWs efficiently suppress the degradation of photoelectrochemical performance by protecting Si surface from oxidation. In conclusion, various spectroscopic analyses revealed that the CNWs-SiNWs simultaneously played a key role in both as catalysts and electrodes, providing a new strategy to develop a new type of metal-free carbon-based structures with enhanced stability and catalytic reactivity essential for the higher performance of hydrogen evolution reaction. Thus, we believe that the CNWs-SiNWs photoelectrodes would provide a new route to develop high-performing cost-effective catalysts essential for advanced energy conversion and storage technologies.

Nano-Confined Sulfur/CNT Composite As Cathode for Li-S Batteries

Sulfur is one of the most promising cathode candidates for lithium batteries for emerging advanced energy storage technology, portable electronics, electric vehicles, and grid-scale energy station. Its overwhelming advantages include abundance, low cost, environmentally friendly and most importantly, high theoretical capacity (1675 mAh g-1) and energy density (2600 vs 387 Wh kg-1 of traditional Li-ion batteries) [1-3]. However, there are major issues which hindered the practical application of lithium-sulfur (Li-S) batteries such as rapid fading of specific capacity, low columbic efficiency and low cycle life due to the “shuttle effect” during charge/discharge process. Here, we present a study using acid treated carbon nanotubes (CNT) as a nano-confinement material for sulfur to develop high areal loading and areal capacity sulfur/CNT composite as cathode for Li-S batteries with a goal to achieve high performance with high specific capacity and long cycle life [4]. During the synthesis process, CNT is segmented to relatively short length followed by chemical reaction deposition and heat treatment to encapsulate sulfur. Morphology of the electrode is characterized by SEM. Crystal structures and mapping results of the sample are determined by XRD and EDS. The sulfur loading in the composition is determined by TGA. Surface characterization is investigated by FTIR. Electrochemical testing is further performed in half-cells using lithium foil as counter and reference electrode and evaluated by cyclic-voltammetry (CV), galvanostatic charge/discharge cycle test and electrochemical impedance spectroscopy (EIS). The detailed results of specific capacity, rate capability, and cyclability will be presented and discussed during the conference.

Experimental and analytical evaluation of a hydro-pneumatic compressed-air Ground-Level Integrated Diverse Energy Storage (GLIDES) system

In recent times, there has been a significant increase in intermittent renewable electricity capacity additions to the generation mix. This, coupled with an aging electrical grid that is poorly equipped to handle the ensuing mismatch between generation and use, has created a strong need for flexible, advanced bulk energy storage technologies. In this paper, one such technology recently invented and demonstrated at Oak Ridge National Laboratory is introduced and characterized. Similar to compressed-air energy storage, the Ground-Level Integrated Diverse Energy Storage (GLIDES) technology is based on gas compression/expansion, however, liquid-piston compression and expansion are utilized. In common with pumped-storage hydroelectricity, hydraulic turbomachines (pump/turbine) are utilized for energy storage and recovery, however, pressure vessels are utilized to create artificial elevation (head) difference, allowing pressure head of several thousands of feet to be reached. This paper reports on the experimental performance of the first GLIDES proof-of-concept prototype, and presents formulation and results from a validated physics-based simulation model.

Energy policy regime change and advanced energy storage: A comparative analysis

This paper employs a multi-level perspective approach to examine the development of policy frameworks around energy storage technologies. The paper focuses on the emerging encounter between existing social, technological, regulatory, and institutional regimes in electricity systems in Canada, the United States, and the European Union, and the niche level development of advanced energy storage technologies. The structure of electricity systems as vertically integrated monopolies, or liberalized or semi-liberalized markets, is found to provide different mechanisms for niche formation and niche to regime transition pathways for energy storage. Significant trade-offs among these pathways are identified. The overwhelming bulk of energy storage policy development activities are found to be taking place in liberalized or semi-liberalized markets. The key policy debates in these markets relate to technical barriers to market participation by storage resources, the ability of storage technologies to offer multiple services in markets simultaneously, the lack of clear rules related to the aggregation of distributed energy resources, and issues related to the meaning of “technological neutrality” in liberalized market systems. Landscape conditions, particularly jurisdictional commitments to pursue deliberate reconfigurations of their energy systems towards low-carbon energy sources, emerge as the most significant factor in the implementation of policy reforms in these areas.

Radical disruption – renewables, technology and the arrival of ‘peak gas'

Debate on the timing of peak oil has become mainstream, as shifting energy demand patterns are compounded by the accelerating threat from disruptive technology such as EVs. At the same time, natural gas demand is seen as a beneficiary of these changes – the much-vaunted transition fuel to a low carbon future. But what might happen to long-term gas demand when factors that could radically reshape energy markets become entrenched? Improvements in energy efficiency, growth in renewables, major advances in energy storage technologies and access to decarbonised electricity are now raising the prospect of ‘peak gas’. In this paper, Wood Mackenzie presents an examination of the key uncertainties impacting the future of gas demand globally, including: • How quickly can technologies such as batteries and storage be developed and what constraints might they face? • Could environmental policy and falling costs mean we are currently underestimating the future growth in renewables – specifically wind and solar power? • How are oil and gas companies responding to the challenges that lie ahead? The impact of these developments will be critical for gas and liquefied natural gas (LNG) producers as they assess the timing, returns and demand for future gas supply. Indeed, for Australian developers these uncertainties could be enough to stop multi-billion-dollar LNG projects taking final investment decisions as early as the 2020s. Wood Mackenzie argues that the time for companies to address peak gas is now – the dynamics of marginal change will likely mean markets will be reshaped sooner than the industry is currently prepared to acknowledge.