No abstract

Despite the outstanding gravimetric performance of lithium–sulfur (Li–S) batteries, their practical volumetric energy density is normally lower than that of lithium‐ion batteries, mainly due to the low density of nanostructured sulfur as well as the porous carbon hosts. Here, a novel approach is developed to fabricate high‐density graphene bulk materials with “ink‐bottle‐like” mesopores by phosphoric acid (H3PO4) activation. These pores can effectively confine the polysulfides due to their unique structure with a wide body and narrow neck, which shows only a 0.05% capacity fade per cycle for 500 cycles (75% capacity retention) for accommodating polysulfides. With a density of 1.16 g cm−3, a hybrid cathode containing 54 wt% sulfur delivers a high volumetric capacity of 653 mA h cm−3. As a result, a device‐level volumetric energy density as high as 408 W h L−1 is achieved with a cathode thickness of 100 µm. This is a periodic yet practical advance to improve the volumetric performance of Li–S batteries from a device perspective. This work suggests a design principle for the real use Li–S batteries although there is a long way ahead to bridge the gap between Li–S batteries and Li–ion batteries in volumetric performance.

4,4′-Dimethylbiphenyl (DMBP) is a promising platform chemical for the production of polymer precursors, plasticizers, and metal–organic frameworks among other materials. We report a two-step process to produce DMBP from 2-methylfuran (MF) via the formation of the intermediate 5,5′-dimethyl-2,2′-bifuran (DMBF). DMBF is generated from the Pd-catalyzed oxidative coupling of MF in the presence of trifluoroacetic acid (TFA) with high selectivity (94%). Optimization of reaction conditions yields a 20-fold increase in site-time-yield (STY = 6.99 h–1) compared with a previously reported protocol. High O2 pressure (7 bar) and a high TFA concentration (3 M) are critical to improve the DMBF formation rate. For the conversion of DMBF to DMBP, we show that phosphoric acid supported on silica (P-SiO2) catalyzes tandem Diels–Alder and dehydration reactions of DMBF with ethylene to produce DMBP (83% yield). The high yield and selectivity are a consequence of the weak Brønsted acid sites in P-SiO2 that dehydrate furan-ethylene cycloadducts without substantial formation of carbon deposits.