MoS 2 has important applications in (electro)catalysis. As with other two-dimensional materials, properties can be highly geometry-dependent; the surface of MoS 2 is catalytically inactive, but the edges can act as active sites for catalyzing reactions. For this reason, device engineering and fabrication may involve considerations for maximizing catalytic surface area, for example by using small nanoparticles rather than large sheets or depositing the sheets vertically rather than horizontally. Catalytic efficiency also depends strongly on the phase: the aforementioned electronic properties of 2H MoS 2 make it a poor candidate for catalysis applications, but these issues can be circumvented through a transition to the metallic (1T) phase. The 1T phase has more suitable properties, with a current density of 10 mA/cm, an overpotential of −187 mV relative to RHE, and a Tafel slope of 43 mV/decade (compared to 94 mV/decade for the 2H phase).