Molybdenum disulphide exhibits two possible crystal states, the naturally occurring semiconducting phase (2H-MoS₂), and the non-naturally occurring metallic state (1T-MoS₂) which can be prepared by intercalation chemistry.¹ The metallic 1T phase has a conductivity up to 10⁷ times higher than the 2H phase.² Consequently, metallic phase MoS₂ 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-MoS₂ was 20 times higher than the gravimetric capacitance of the 2H-MoS₂.²

In this work, we compare the capacitive behaviour of 1T-MoS₂, 2H-MoS2, graphene and 1T-MoS₂/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-MoS₂ was over 100 F g^-1 in aqueous solution which is higher than the gravimetric capacitance obtained using 2H-MoS₂ or graphene electrodes. The capacitance performance of 1T-MoS₂ 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-MoS₂ 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.