Hierarchical NiMoS and NiFeS Nanosheets with Ultrahigh Energy Density for Flexible All Solid‐State Supercapacitors

Abstract

Highly flexible supercapacitors (SCs) have great potential in modern electronics such as wearable and portable devices. However, ultralow specific capacity and low operating potential window limit their practical applications. Herein, a new strategy for the fabrication of free-standing NiMoS and NiFeS nanosheets (NSs) for high-performance flexible asymmetric SC (ASC) through hydrothermal and subsequent sulfurization technique is reported. The effect of Ni 2+ is optimized to attain hierarchical NiMoS and NiFeS NS architectures with high electrical conductivity, large surface area, and exclusive porous networks. Electrochemical properties of NiMoS and NiFeS NS electrodes exhibit that both have ultrahigh specific capacities (≈312 and 246 mAh g −1 at 1 mA cm −2 ), exceptional rate capabilities (78.85% and 78.46% capacity retention even at 50 mA cm −2 , respectively), and superior cycling stabilities. Most importantly, a flexible NiMoS NS//NiFeS NS ASC delivers a high volumetric capacity of ≈1.9 mAh cm −3 , excellent energy density of ≈82.13 Wh kg −1 at 0.561 kW kg −1 , exceptional power density (≈13.103 kW kg −1 at 61.51 Wh kg −1 ) and an outstanding cycling stability, retaining ≈95.86% of initial capacity after 10 000 cycles. This study emphasizes the potential importance of compositional tunability of the NS architecture as a novel strategy for enhancing the charge storage properties of active electrodes.

Homogeneous Core/Shell NiMoO4@NiMoO4 and Activated Carbon for High Performance Asymmetric Supercapacitor

“…The maximum capacities of Electrodes I and III are much lower and can only reach 309 mA h/g (371 µA h/cm 2 ) and 324 mA h/g (453 µA h/cm 2 ), respectively, over 25% and 21% lower than that of Electrode II. Notably, the specific capacity of our homogeneous architecture here is favorably comparable with those of previously reported nanostructures, including CoMoO 4 @Co(OH) 2 core-shell structures (265 mA h/cm 2 at 2 mA/cm 2 ) [46], as well as CoMoO 4 nanoflakes (32.40 mA h/g; 492.48 µAh/cm 2 ) [47], Ni–Mo–S nanosheets (312 mA h/g at 1 mA/cm 2 ) [48], and flower-like Mn–Co oxysulfide (136 mA h/g at 2 A/g) [49]. Detailed comparisons in electrochemical performances among these devices and our structure can be found in Table S1.…”

Freestanding 1T‐MnxMo1–xS2–ySey and MoFe2S4–zSez Ultrathin Nanosheet‐Structured Electrodes for Highly Efficient Flexible Solid‐State Asymmetric Supercapacitors

“…Peaks at 55.1 and 53.8 eV are assigned to 3d 3/2 and 3d 5/2 of Se 3d. [ 21–23,26 ] The above‐discussed XPS results indicated the formation of 1T‐Mn x Mo 1− x S 2− y Se y and were found in accordance with the other reported literatures. [ 10,13–18 ]…”

“…[ 10,13–18 ] GCD curves for the 1T‐Mn x Mo 1− x S 2− y Se y at different current densities (1 to 50 mA cm −2 ) showed a near symmetric nature in charging and discharging time (Figure 4E) justifying the excellent coulombic efficiency of the electrode. [ 10–19,22–26 ] The highest potential window in the GCD curve at current density 1 mA cm −2 for MoS 2 was found to be ≈0.36 V (similar to the other reported literature of MoS 2 ) [ 24 ] and remained similar for 1T‐Mn x Mo 1− x S 2− y Se y too (Figure 4E) .…”

Interface engineering induced NiFe/Ni-Mo-S@CC heterostructure with excellent OER and HER performance

“…3a shows the strong peaks at 858.38 and 875.88 eV with the binding energy difference of 17.5 eV in Ni-Mo-S@CC, corresponding to the low band of Ni 2p 3/2 and high band of Ni 2p 1/2 , respectively, consistent with the previous reports [32]. The intense satellite peak suggested that the Ni 2+ state was predominant in the Ni 2p spectra [33]. After electrodepositing metal Fe, a slight negative shift of about 0.96 eV can be found in the binding energy of Ni 2p 3/2 (857.42 eV) and Ni 2p 1/2 (874.92 eV) for Fe/Ni-Mo-S@CC compared with those for Ni-Mo-S@CC, con rming the electron transfer from Fe metal to Ni in Ni-Mo-S. After electrodepositing metal Ni, a slight negative shift of about 1.31 eV can be found in the low band of Ni 2p 3/2 (857.07 eV) for Ni/Ni-Mo-S@CC compared with that of Ni-Mo-S@CC, con rming the electron transfer from Ni metal to Ni in Ni-Mo-S. Identically, the Ni 2p peaks in NiFe/Ni-Mo-S@CC show negative shift of 1.63 eV compared with that of Ni-Mo-S@CC, demonstrating the strong electron interaction between NiFe and Ni-Mo-S.…”