No abstract

Here we report a new redox-active perylene bisimide (PBI)polysulfide (PS) gel that overcomes electronic charge-transport bottlenecks common to lithium−sulfur (Li−S) hybrid redox flow batteries designed for long-duration grid-scale energy storage applications. PBI was identified as a supramolecular redox mediator for soluble lithium polysulfides from a library of 85 polycyclic aromatic hydrocarbons by using a high-throughput computational platform; furthermore, these theoretical predictions were validated electrochemically. Challenging conventional wisdom, we found that π-stacked PBI assemblies were stable even in their reduced state through secondary interactions between PBI nanofibers and Li 2 S n , which resulted in a redoxactive, flowable 3-D gel network. The influence of supramolecular charge-transporting PBI-PS gel networks on Li−S battery performance was investigated in depth and revealed enhanced sulfur utilization and rate performance (C/4 and C/8) at a sulfur loading of 4 mg cm −2 and energy density of 44 Wh L −1 in the absence of conductive carbon additives.

We report a method for the highly enantioselective CuH-catalyzed allylation of ketones that employs terminal allenes as allylmetal surrogates. Ketones and allenes bearing diverse and sensitive functional groups are efficiently coupled with high stereoselectivity and exclusive branched regioselectivity. In stoichiometric experiments, each elementary step of the proposed hydrocupration-addition-metathesis mechanism can be followed by NMR spectroscopy.

The charge-transporting ability of supramolecular polymer networks assembled from hexabenzocoronenes (HBCs) in nonaqueous electrolyte is reported here for the first time. Enhanced electronic conductivity is observed when the HBC subunits are chemically oxidized to radical cations, which is rationalized using density functional theory.Organic semiconductors with tunable, well-behaved charge transport have led to exciting advances for a broad range of (opto)electronic, photovoltaic and sensing technologies. 1 Recent work further highlights opportunities to integrate these materials in electrochemical devices. 2 Along these lines, we were interested in understanding their charge-transporting properties in electrolytes, toward flowable electrodes 3 with both ion and electron transport ability. Here, the electrolyte carries the ion current and the embedded organic semiconductor can be triggered, by some chemical or electrochemical means, to transport the electrons (or holes). For comparison, carbon nanomaterials with metallic or semi-metallic character confer static electronic conductivity when dispersed in electrolyte, but also improves when their loading exceeds a percolation threshold, indicating 3-D network formation is critical. 4 Notably, these nanomaterials are compositionally heterogeneous and offer limited means of tuning network conductivity and architecture through molecular engineering. 5 We hypothesized that supramolecular polymers of polycyclic aromatic hydrocarbons 6 (PAHs) would provide an attractive platform with modular tunability (Fig. 1). Achieving success in this regard would depend on the ability of these materials to assemble into nanowires and networks in electrolyte and, furthermore, be induced to transport charge (e.g., via a hopping mechanism 7 ). Here, we show that a new hexa-peri-hexabenzocoronene (HBC) assembles in non-aqueous electrolyte, and achieves mixed ion-and electronic-conductivity when HBC radical cations are introduced to the assembly (Fig. 1B). Up to 20-fold gains in shuttling current are demonstrated for HBC/HBC •+ mixed nanowire assemblies compared to assemblies of undoped HBC. We rationalize this behaviour using density functional theory (DFT), which supports a highly delocalized Fig. 1 Schematic representation of HBC assembly into supramolecular networks in liquid electrolyte (A) and subsequent chemical doping by HBC radical cations, which enhance the electronic charge transporting ability of the network (B). † Electronic supplementary information (ESI) available: Synthesis and characterization of all compounds, computational details, experimental details for optical spectroscopy, X-ray spectroscopy, EPR spectroscopy, and electrochemical measurements. See