Structure-tunable supraparticle assemblies of hollow cupric oxide sheathed with nanographenes.

Self-assembled supraparticles (SPs), a secondary structure of clustered nanoparticles, have attracted considerable interest owing to their highly tunable structure, composition, and morphology from their primary nanoparticle constituents. In this study, hierarchically assembled hollow Cu2O SPs were prepared using a cationic polyelectrolyte poly(diallyl dimethylammonium chloride) (PDDA) during the formation of Cu2O nanoparticles. The concentration-dependent structural transformation of PDDA from linear chains to assembled droplets plays a crucial role in forming a hollow colloidal template, affording the self-assembly of Cu2O nanoparticles as a secondary surfactant. The use of the positively charged PDDA also affords negatively charged nanoscale graphene oxide (NGO), an electrical and mechanical supporter to uniformly coat the surface of the hollow Cu2O SPs. Subsequent thermal treatment to enhance the electrical conductivity of NGO within the NGO/Cu2O SPs allows for the concomitant phase transformation of Cu2O to CuO, affording reduced NGO/CuO (RNGO/CuO) SPs. The uniquely structured hollow RNGO/CuO SPs achieve improved electrochemical properties by providing enhanced electrical conductivity and electroactive surface area.

Nanoporous aramid nanofibre separators for nonaqueous redox flow batteries.

Redox flow batteries are attractive for large-scale energy storage due to a combination of high theoretical efficiencies and decoupled power and energy storage capacities. Efforts to significantly increase energy densities by using nonaqueous electrolytes have been impeded by separators with low selectivities. Here, we report nanoporous separators based on aramid nanofibres, which are assembled using a scalable, low cost, spin-assisted layer-by-layer technique. The multilayer structure yields 5 ± 0.5 nm pores, enabling nanofiltration with high selectivity. Further, surface modifications using polyelectrolytes result in enhanced performance. In vanadium acetylacetonate/acetonitrile-based electrolytes, the coated separator exhibits permeabilities an order of magnitude lower and ionic conductivities five times higher than those of a commercial separator. In addition, the coated separators exhibit exceptional stability, showing minimal degradation after more than 100 h of cycling. The low permeability translates into high coulombic efficiency in flow cell charge/discharge experiments performed at cycle times relevant for large-scale applications (5 h).

Feasibility of a Supporting-Salt-Free Nonaqueous Redox Flow Battery Utilizing Ionic Active Materials.

Nonaqueous redox flow batteries (NAqRFBs) are promising devices for grid-scale energy storage, but high projected prices could limit commercial prospects. One route to reduced prices is to minimize or eliminate the expensive supporting salts typically employed in NAqRFBs. Herein, the feasibility of a flow cell operating in the absence of supporting salt by utilizing ionic active species is demonstrated. These ionic species have high conductivities in acetonitrile (12-19 mS cm-1 ) and cycle at 20 mA cm-2 with energy efficiencies (>75 %) comparable to those of state-of-the-art NAqRFBs employing high concentrations of supporting salt. A chemistry-agnostic techno-economic analysis highlights the possible cost savings of minimizing salt content in a NAqRFB. This work offers the first demonstration of a NAqRFB operating without supporting salt. The associated design principles can guide the development of future active species and could make NAqRFBs competitive with their aqueous counterparts.

Mechanism-Based Development of a Low-Potential, Soluble, and Cyclable Multielectron Anolyte for Nonaqueous Redox Flow Batteries.

The development of nonaqueous redox flow batteries (NRFBs) has been impeded by a lack of electroactive compounds (anolytes and catholytes) with the necessary combination of (1) redox potentials that exceed the potential limits of water, (2) high solubility in nonaqueous media, and (3) high stability toward electrochemical cycling. In addition, ideal materials would maintain all three of these properties over multiple electron transfer events, thereby providing a proportional increase in storage capacity. This paper describes the mechanism-based design of a new class of metal-coordination complexes (MCCs) as anolytes for NRFBs. The tridentate bipyridylimino isoindoline (BPI) ligands of these complexes were designed to enable multielectron redox events. These molecules were optimized using a combination of systematic variation of the BPI ligand and the metal center along with mechanistic investigations of the decomposition pathways that occur during electrochemical cycling. Ultimately, these studies led to the identification of nickel BPI complexes that could undergo stable charge-discharge cycling (<5% capacity loss over 200 cycles) as well as a derivative that possesses the previously unprecedented combination of high solubility (>700 mM in CH3CN), multiple electron transfers at low redox potentials (-1.7 and -1.9 V versus Ag/Ag+), and high stability in the charged state for days at high concentration. Overall, the studies described herein have enabled the identification of a promising anolyte candidate for NRFBs and have also provided key insights into chemical design principles for future classes of MCC-based anolytes.

Twelve Principles for Green Energy Storage in Grid Applications.

The introduction of energy storage technologies to the grid could enable greater integration of renewables, improve system resilience and reliability, and offer cost effective alternatives to transmission and distribution upgrades. The integration of energy storage systems into the electrical grid can lead to different environmental outcomes based on the grid application, the existing generation mix, and the demand. Given this complexity, a framework is needed to systematically inform design and technology selection about the environmental impacts that emerge when considering energy storage options to improve sustainability performance of the grid. To achieve this, 12 fundamental principles specific to the design and grid application of energy storage systems are developed to inform policy makers, designers, and operators. The principles are grouped into three categories: (1) system integration for grid applications, (2) the maintenance and operation of energy storage, and (3) the design of energy storage systems. We illustrate the application of each principle through examples published in the academic literature, illustrative calculations, and a case study with an off-grid application of vanadium redox flow batteries (VRFBs). In addition, trade-offs that can emerge between principles are highlighted.

Evaluation of Tris-Bipyridine Chromium Complexes for Flow Battery Applications: Impact of Bipyridine Ligand Structure on Solubility and Electrochemistry.

This report describes the design, synthesis, solubility, and electrochemistry of a series of tris-bipyridine chromium complexes that exhibit up to six reversible redox couples as well as solubilities approaching 1 M in acetonitrile. We have systematically modified both the ligand structure and the oxidation state of these complexes to gain insights into the factors that impact solubility and electrochemistry. The results provide a set of structure-solubility-electrochemistry relationships to guide the future development of electrolytes for nonaqueous flow batteries. In addition, we have identified a promising candidate from the series of chromium complexes for further electrochemical and battery assessment.

High activity carbide supported catalysts for water gas shift.

Nanostructured carbides are refractory materials with high surface areas that could be used as alternatives to the oxide materials that are widely used as support materials for heterogeneous catalysts. Carbides are also catalytically active for a variety of reactions, offering additional opportunities to tune the overall performance of the catalyst. In this paper we describe the synthesis of molybdenum carbide supported platinum (Pt/Mo(2)C) catalysts and their rates for the water gas shift reaction. The synthesis method allowed interaction of the metal precursor with the native, unpassivated support. The resulting materials possessed very high WGS rates and atypical Pt particle morphologies. Under differential conditions, rates for these catalysts were higher than those for the most active oxide-supported Pt catalysts and a commercial Cu-Zn-Al catalyst. Experimental and computational results suggested that active sites on the Pt/Mo(2)C catalysts were located on the perimeter of the Pt particles and that strong interactions between Pt and the Mo(2)C surface gave rise to raft-like particles.