A theoretical investigation is highly important to investigate the properties of materials, the origin of selectivity, and the effect of various parameters in designing promising electrode materials for supercapacitor applications. The latest research paper by Mr Samadhan Kapse, PhD Student in the Department of Physics, and Prof Ranjit Thapa, Associate Dean of SEAMS (Sciences), envisions this and developed a novel VS2-BP hybrid electrode material. Their article titled All-solid-state Supercapacitor Based on Advanced 2D Vanadium disulfide/Black Phosphorus Hybrids for Wearable Electronics has been published in the journal ACS Applied Energy Materials with an impact factor of 6.959.

Abstract

Vanadium disulfide-Black Phosphorus (VS2-BP) hybrids were synthesised by a one-pot hydrothermal assisted method to achieve enhanced electrochemical activity for supercapacitor applications. The concentration of BP was optimised to prevent the restacking nature of VS2 and to enrich the active edges for electrolytic ion intercalation. The charge storage kinetics of the best-performing VS2-BP as an active electrode has demonstrated the dominance of the pseudocapacitive nature of the material. Further, by sandwiching with PVA/K2SO4 gel electrolyte, an all-solid-state (ASS) Vanadium disulfide/Black Phosphorus-50 mg (VS2-BP-50) symmetric device was developed on highly conductive carbon paper. The ASS VS2-BP-50 symmetric device displays the highest specific areal capacitance of 203.25 mF/cm2. It exhibits the maximum areal energy density of 28.22 µW h cm-2 at an areal power density of 596.09 mW cm-2, outperforming previous literature. We used density functional theory to understand the origin of high quantum capacitance. We found that the charge accumulation region between VS2 and BP monolayers and the charge transfer is the origin of the improved density of states in the VS2-BP hybrid. Also, we observed the higher mobility of K+ ion and a higher diffusion rate using the Density functional theory (DFT) method.

Explanation of the research

A novel VS2-BP hybrid electrode material was prepared using a simple hydrothermal approach. Due to a synergistic effect, it was discovered that adding BP to metallic VS2 enhances the number of electrochemically active sites, resulting in increased surface activity. It also accelerates reaction kinetics with electrolyte ions by improving the electrical behaviour of active electrode material. As a result, the hybrid technique overcomes the weaknesses of individual components during electrochemical processes, resulting in increased performance that has been limited by individuals. The BP nanosheets behaved as a pore region for electron transport and prevented the VS2 layers from re-stacking. Systematic experiments are conducted by selecting the ideal precursor ratios to generate a high-quality VS2-BP hybrid with enhanced electronic conductivity. Furthermore, in the overall collective charge storage of the VS2-BP-50 hybrid material, the present results demonstrated that capacitive contributions outnumber diffusive contributions. The ASS VS2-BP-50 symmetric supercapacitor device was also designed to have a high areal capacitance of 203.25 mF/cm2 with a maximum areal power density of 596.09 mW cm-2. The extraordinary performance of the ASS VS2-BP-50 symmetric device illustrates its versatility in terms of designing a high-power density ASS supercapacitor for flexible and wearable device applications. The work functions of BP, VS2, and VS2-BP are 0.73 eV, 5.37 eV, and 4.99 eV, respectively, which help in the charge transfer mechanism and increase the density of state at the Fermi level, and subsequently, the quantum capacitance of the heterostructure.

Collaborations

1. Mr Aditya Sharma, Centre for Nano and Material Sciences, Jain Global Campus, Jakkasandra, Ramanagaram, Bangalore – 562112, Karnataka, India

2. Mr Ankur, Centre for Nano and Material Sciences, Jain Global Campus, Jakkasandra, Ramanagaram, Bangalore – 562112, Karnataka, India

3. Mr Sagar Bisoyi, Department of Physics, School of Applied Sciences, KIIT Deemed to be University, Bhubaneswar-751024, Odisha, India.

4. Dr Gopal K. Pradhan, Department of Physics, School of Applied Sciences, KIIT Deemed to be University, Bhubaneswar-751024, Odisha, India.

5. Dr Chandra Sekhar Rout, Centre for Nano and Material Sciences, Jain Global Campus, Jakkasandra, Ramanagaram, Bangalore – 562112, Karnataka, India

Social implications of the research

With the exponential development of portable/flexible electronics and the high demand for renewable energy, conventional energy-storage devices, such as supercapacitors, have attracted attention due to their benefits of fast charge/discharge rates, long cycle life, and high-power density. Similarly, developing novel functional materials with exceptional qualities could shed light on a plethora of challenges, including environmental pollution, energy crisis, etc. Two-dimensional (2D) layered materials, such as metallic 1T MoS2 single layers, SnSe2, MXenes, and black phosphorous (BP), have been intensively studied for supercapacitor applications. These materials benefit from efficient ion intercalation and electrosorption. The two-dimensional (2D) layered transition-metal dichalcogenides (TMDs) have recently piqued the scientific community’s curiosity.