Long Xia

Abstract Ammonium‐ion aqueous supercapacitors are raising notable attention owing to their cost, safety, and environmental advantages, but the development of optimized electrode materials for ammonium‐ion storage still lacks behind expectations. To overcome current challenges, here, a sulfide‐based composite electrode based on MoS 2 and polyaniline (MoS 2 @PANI) is proposed as an ammonium‐ion host. The optimized composite possesses specific capacitances above 450 F g −1 at 1 A g −1 , and 86.3% capacitance retention after 5000 cycles in a three‐electrode configuration. PANI not only contributes to the electrochemical performance but also plays a key role in defining the final MoS 2 architecture. Symmetric supercapacitors assembled with such electrodes display energy densities above 60 Wh kg −1 at a power density of 725 W kg −1 . Compared with Li + and K + ions, the surface capacitive contribution in NH 4 + ‐based devices is lower at every scan rate, which points to an effective generation/breaking of H‐bonds as the mechanism controlling the rate of NH 4 + insertion/de‐insertion. This result is supported by density functional theory calculations, which also show that sulfur vacancies effectively enhance the NH 4 + adsorption energy and improve the electrical conductivity of the whole composite. Overall, this work demonstrates the great potential of composite engineering in optimizing the performance of ammonium‐ion insertion electrodes.

Abstract The use of non‐metal charge carriers such as ammonium (NH 4 + ) in electrochemical energy storage devices offers advantages in terms of weight, element abundance, and compatibility with aqueous electrolytes. However, the development of suitable electrodes for such carriers lags behind other technologies. Herein, we present a high‐performance anode material for ammonium‐ion supercapacitors based on a MoO 3 /carbon (MoO 3 @C) composite. The NH 4 + storage performance of such composites and their practical application prospects are evaluated both in a three‐electrode configuration and as symmetric supercapacitors. The optimized material reaches an unprecedented specific capacitance of 473 F·g −1 (158 mAh·g −1 ; 1592 mF·cm −2 ) at a current density of 1 A·g −1 , and 92.7% capacitance retention after 5000 cycles in a three‐electrode set‐up. This outstanding performance is related to the presence of oxygen vacancies that enhance the composites’ ionic/electronic transportation and electrochemical reaction site, while at the same time facilitating the formation of hydrogen bonds between NH 4 + and the host material. Using the optimized composite, symmetric supercapacitors based on an (NH 4 ) 2 SO 4 gel electrolyte are fabricated and demonstrated to provide unmatched energy densities above 78 Wh·kg −1 at a power density of 929 W·kg −1 . Besides, such devices are characterized by extraordinary capacitance retention of 97.6% after 10,000 cycles.

While asymmetric supercapacitors (ASCs) have huge potential as efficient, durable, and cost-effective energy storage devices, they fail to meet expectations because of the unoptimized architecture and composition of their electrode materials. Herein, PPy/PANI@MoS2 (PPMS) ternary composites with a dual-channel structure are obtained by facile hydrothermal and in situ polymerization methods. These dual conductive channels synergistically improve the electrode’s electrical conductivity, facilitate ion diffusion, enlarge the interlayer distance, and increase the accessible surface area. Taking advantage of such a favorable architecture, PPMS composites exhibit outstanding electrochemical properties, including a huge specific capacitance (1171 F g–1 at 1 A g–1) and rate capability (861 F g–1 at 20 A g–1) in three-electrode systems. Based on charge storage mechanism analyses, we demonstrate that the kinetic behavior of PPMS electrodes is dominated by the surface capacitance (95.9% at 100 mV s–1). Besides, PPMS-based ASCs (PPMS//activated carbon) operate in a broad voltage window (1.8 V), delivering an ultrahigh energy density of 93.4 Wh kg–1 at a power density of 884.8 W kg–1. They also show a superior cycling stability of 90.4% and a remarkable Coulombic efficiency of 99.2% for 10,000 cycles. This work affords an inspiration for rational structural optimization of PANI-based electrode materials with great prospects in the development of next-generation high energy density ASCs.