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Searching for catalysts of hydrogen evolution reaction (HER) that can replace Pt is critical. Here, we investigated the HER electrocatalytic activity of pentagonal PdS2 (penta-PdS2) and PdSe2 (penta-PdSe2) by first-principles calculations. Three types of vacancies (VS/Se, VPd, DVS/Se) were constructed to activate the inert basal planes of PdS2 and PdSe2. The results show that S/Se and Pd vacancies significantly improve HER performance, and the Gibbs free energy (ΔGH) of systems can be further regulated by vacancy concentration. Particularly, PdS2 with 2.78% VS, 50% VPd and PdSe2 with 12.5% VSe display the optimal ΔGH value and the highest exchange current density. Further analysis of charge transfer and band structures were described that the introduce of vacancies efficiently regulates the electronic properties, resulting in the diminution of bandgap, and accelerates the charge transfer, thereby contributing to an enhanced electron environment for HER process. Our results provide a theoretical guidance for the applications of pentagonal transition-metal dichalcogenides as catalysts of hydrogen evolution reaction.

With the rapid development in portable and wearable electronics, it will be of great convenience if flexible supercapacitors can be easily mounted/disassembled from different substrates at our will, which will largely expand their application scenarios. Herein, inspired by a sticky note, a new family of flexible sticky-note supercapacitors with repeated adhesive performance has been developed by employing a novel kind of sticky aligned carbon nanotube array electrode. The sticky-note supercapacitor demonstrated high capacitance and can be easily and repeatedly attached onto various substrates including cloth, glass, paper, plastic and metal. For up to 200 attaching/removing cycles on different substrates, the capacitance of the supercapacitor note can be well maintained at above 99%.

Stretchable supercapacitors are critical for a variety of portable and wearable electronic devices, and they have been typically realized by the use of non-active elastic substrates that do not contribute to the energy storage capability. Here a new family of stretchable supercapacitors is fabricated from cellular carbon nanotube film-based electrodes with high electrochemical performances. They display high specific capacitances that can be maintained by 98.3% after stretching by 140% for 3000 cycles. In addition, their voltage and current windows are tuned by varying the configuration of the film electrode.

A three-dimensionally stretchable supercapacitor is created by designing a novel pyramid structure without the use of an elastic substrate. Compared with previous stretchable supercapacitors that may deform in plane on elastic substrates, these pyramid-structured supercapacitors can be stretched in three dimensions with high stability. Their electrochemical performances are well maintained after stretching in three dimensions for thousands of cycles, and they show both higher energy and power densities compared with the other reported stretchable supercapacitors. In addition, they are breathable due to the designed grooves that produce the pyramid structure, which is particularly promising for many emerging applications such as wearable electronics. This work further provides an effective strategy for developing next-generation flexible electronic devices with high performances.

Poly(ether sulfone) (PES) porous membranes with tunable morphology were fabricated via a phase inversion method and applied in vanadium flow batteries (VFBs). The morphology of the PES membrane was adjusted by changing the polymer concentration and blending with hydrophilic sulfonated poly(ether ether ketone) (SPEEK) in the cast solution. The relationship between the membrane morphology and the performance in VFBs was investigated in detail. The results indicated that with increasing polymer concentration of the cast solution, the number of macrovoids gradually decreased and the finger-like pores became larger. A higher coulombic efficiency (CE) can be obtained due to the lower vanadium permeability, while the voltage efficiency (VE) decreased. In addition, the introduction of SPEEK in cast solution will induce the transformation of membrane structures from finger-like to spongy-like pores. The CE decreased with the higher vanadium permeability, while the VE increased due to the increased proton conductivity. As a result, optimized VFB performance of the PES membranes was obtained, showing a CE of 92.8% and an energy efficiency (EE) of 78.4%. The battery assembled with the prepared membranes showed a stable battery performance after running for more than 200 cycles, showing good oxidation stability. This work presents an effective and facile method to fabricate PES membranes with tunable battery performance.

An ultrathin Nafion film was introduced onto the poly(ether sulfone) (PES)-sulfonated poly(ether ether ketone) (SPEEK) porous membranes for vanadium flow battery (VFB) application. The composite membranes showed very high ion selectivity, good stability and excellent performance (energy efficiency 86.5% at 80 mA cm(-2)) in VFB.

A solvent-template method is proposed for manufacturing ion conducting membranes (ICMs) with controlled ion transport channels (in nano-scale) for vanadium flow battery (VFB) application. As a result, the ion transport properties and single cell performance of the ICMs could be easily tuned by this method. The VFB single cell assembled with the prepared ICMs achieved CE over 99% and EE over 92% when operated under a current density of 40 mA cm−2, which is among the excellent performances ever studied for VFB porous ICMs. The solvent-template method proposed in this article is promising for fabricating high performance ICMs for the VFB as well as other potential battery systems.