Strain and defect-engineering on the basal plane of ultra-large MoS2 monolayers attached onto stretchable gold electrodes

Abstract

Strain and defect-engineering methods have been widely used to tune a variety of properties of monolayer MoS₂ towards optical, electronic, mechanical, and electrochemical applications. For electrochemical applications in the field of energy, i.e. hydrogen evolution reaction (HER), defects act as catalytic sites to promote this reaction. Thus, the creation of routes that convert the relatively inert MoS₂ basal plane into an HER-active system plays an essential role in this field. In this work, we report an innovative method that can generate both strain and edge-like defects on ultra-large MoS₂ monolayers anchored onto stretchable gold electrodes. By simply stretching the electrodes, tensile strain, and oriented crack formation were achieved on the basal plane. Raman, photoluminescence, and atomic force microscopy experiments confirmed the presence of strain. Simulation of the stretching process reveals the regions that are more prone to crack, which was experimentally confirmed by scanning electron microscopy and laser scanning confocal microscopy measurements. Density functional theory studies confirm that curvature effects alone do not improve significantly the HER activity, thus emphasizing the need to produce cracks in the MoS₂ monolayers to improve the catalytic activity. Finally, the stretch-induced cracks can reduce the overpotential measured at 10 mA cm⁻² to 352 mV. The electrocatalytic activity is superior when compared to pristine MoS₂ and presents remarkable stability up to 500 cycles.