Featured LetterInvestigation of electrochemical performance of a high surface area mesoporous Mn doped TiO2 nanoparticle for a supercapacitor
Introduction
Development of a suitable electrode materials having high energy density, high power density, long-life cycle and rapid charge/discharge capability is the primary requirement for the high-performing supercapacitor [1], [9]. The carbon-based materials that are used in electrical double-layer capacitors (EDLCs) have higher electrical conductivity, high surface area and remarkable stability but suffer from low specific capacitance because of the limited charge accumulation [2]. By contrast, electrode in pseudocapacitors are usually based on transitional metal oxide and conducting polymers in which the charge is stored by means of reversible surface or near surface redox reaction. However, pseudocapacitive materials often suffer from the gradual loss of capacitance due to low electrical conductivity and irreversible Faradic reaction [3], [4].
A well-known and chemically stable TiO2 has also been attempted as an electrode material in various types of electrochemical devices [5]. However, intrinsic TiO2 phases show limited electrical conductivity originating from its wide energy gap despite possessing excellent cyclic stability. Doping by metals or non-metal dopants on TiO2 alter the intrinsic electronic and optical properties and is one of the effective techniques to improve optoelectronic response of TiO2. Theoretical modelling and DFT studies showed that Mn is deemed to be the most promising 3d transition metal dopant that generates an intermediate donor state within the forbidden gap with less defect sites and better charge mobility [6]. Additionally, the electrochemical performance of an electrode material can be enhanced by increasing the surface area, tailoring the morphology [7]. Thus, a highly mesoporous Mn doped TiO2 nanoparticle was synthesised by a simple two step sol–gel combined solvothermal method using triethanolamine as a pH as well as structure-directing agent. This novel method resulted nearly monodisperse mesoporous Mn-TiO2 nanoparticles with high surface area. This improved surface area and mesoporosity would additionally enhance capacitive properties because of the availability of more active sites. The electrochemical data measured in aqueous three-electrode system showed supercapacitive performance of the nanoparticle is increased by appropriately doping Mn.
Section snippets
Preparation of Mn-TiO2
A typical synthesis of Mn doped TiO2 (Mn-TiO2) was performed by the modification of earlier solvothermal synthesis methods [8]. A precursor solution was prepared by mixing 2 mmol of titanium tetraisopropoxide (TTIP), 0.1 mmol of MnSO4·H2O and 1 mmol of triethanolamine (TEOA) in 20 ml absolute ethanol. After a vigorous stirring for 1 h, a 50 ml ethanolic solution of 1 ml diethylamine and 25 ml water was poured into the precursor solution and again kept stirring for 6 h. The resulting sol was
Results and discussion
Crystal structure of the TiO2 and Mn-TiO2 nanoparticles are shown by XRD patterns in Fig. S1 with all the description. 40 to 50 nm sized TiO2 and 1Mn-TiO2 nanoparticles are shown in Fig. 1(a–b). Fig. 1(c) shows magnified image of 1Mn-TiO2 with small pore like structures on the surface. Fig. 1(d–e) shows the overall HRTEM image and SAED pattern of 1Mn-TiO2 nanoparticles. The interspacing distance 0.324 nm in doped TiO2 shown in the HRTEM indicates the well-developed lattice fringes corresponding
Conclusion
High surface area mesoporous Mn doped TiO2 nanoparticles were synthesised via sol–gel and solvothermal process. These mesoporous 40–50 nm sized Mn-TiO2 nanoparticles were investigated for the electrochemical properties as compared to the pure TiO2. The electrochemical tests showed that the 1 wt% Mn-TiO2 possessed higher capacitance properties compared to the pure TiO2 and other Mn-TiO2. It was found that the manganese doping has exerted significant improvement of the energy storage properties
CRediT authorship contribution statement
Devi Prashad Ojha: Conceptualization, Methodology, Data curation, Writing - original draft, Writing - review & editing. Milan Babu Poudel: Investigation, Data curation. Han Joo Kim: Supervision, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work was supported by National Research foundation, NRF (Grant no. 2017-R1C1B2011968), Republic of Korea. We would also like to acknowledge Centre for Chonbuk University Research Facility (CURF) for providing equipments for analysis.
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