Metallic Phase MoS₂-Graphene Composite for High Performance Coin Cells Supercapacitors

Abstract

Molybdenum disulphide exhibits two possible crystal states, the naturally occurring semiconducting phase (2H-MoS 2 ), and the non-naturally occurring metallic state (1T-MoS 2 ) which can be prepared by intercalation chemistry. 1 The metallic 1T phase has a conductivity up to 10 7 times higher than the 2H phase. 2 Consequently, metallic phase MoS 2 nanosheets are very attractive for a number of electrochemical applications including supercapacitor electrodes and catalysts for hydrogen evolution. 2 , 3 For example, Acerce et al . recently demonstrated that the gravimetric capacitance of chemically exfoliated 1T-MoS 2 was 20 times higher than the gravimetric capacitance of the 2H-MoS 2 . 2 In this work, we compare the capacitive behaviour of 1T-MoS 2 , 2H-MoS2, graphene and 1T-MoS 2 /graphene composite using symmetrical coin cell architecture. The electrodes were prepared by filtering a known volume of the respective dispersion over pre-weighed polyvinylidene fluoride membrane using syringe pump dispenser. The gravimetric capacitance of 1T-MoS 2 was over 100 F g -1 in aqueous solution which is higher than the gravimetric capacitance obtained using 2H-MoS 2 or graphene electrodes. The capacitance performance of 1T-MoS 2 was further enhanced by making a composite electrode with highly conducting graphene. A volumetric capacitance of over 560 F cm -3 in an aqueous solution and 250 F cm -3 in a non-aqueous solution were achieved using these composite electrodes. The composite electrode displayed capacity retention of over 90 % after 5,000 cycles. The enhanced capacitance in the composite material was probably due to a synergistic effect between 1T-MoS 2 and graphene where graphene enhances the overall conductivity of the composite whilst also reducing the re-aggregation of the sheets. 1. M. A. Py and R. R. Haering, Can. J. Phys. , 1983, 61 , 76-84. 2. M. Acerce, D. Voiry and M. Chhowalla, Nat. Nanotechnol. , 2015, 10 , 313-318. 3. M. A. Lukowski, A. S. Daniel, F. Meng, A. Forticaux, L. S. Li and S. Jin, J. Am. Chem. Soc. , 2013, 135 , 10274-10277.