All-Edge MoS by Ultramicrotomy for Hydrogen Evolution.

MoS is a promising catalyst for the hydrogen evolution reaction (HER), with edge sites known to be significantly more active than basal planes. However, the influence of external factors such as edge packing and the distance electrons must traverse through the basal plane remains underexplored, mainly due to the lack of precise MoS structuring methods. Existing approaches typically yield mixtures containing both basal planes and edge sites, limiting control over active site exposure. Here, we developed a slicing-based approach using ultramicrotomy to fabricate MoS structures composed exclusively of edge terminations, with tunable spacing and distances to the underlying electrode. This technique enables strong control over the edge morphology, alignment, and electrochemical accessibility. Benchmarking the HER performance of these precision-sliced all-edge MoS structures on glassy carbon revealed a trend where thinner, more disordered, and open-edge arrangements outperform thicker, compact, and aligned slices. This indicates that catalytic performance depends not only on edge abundance but also on accessibility, geometric openness, and electron transfer resistance in the basal plane. The pristine vMoS-⊥ exhibits an overpotential of ∼300 mV at 10 mA cm, which is higher than some chemically modified MoS systems; however, with Au nanoparticle decoration, the overpotential decreases to 180 mV, comparable to state-of-the-art MoS-based catalysts. Our findings offer mechanistic understanding of HER activity in MoS, provide a platform for rational edge engineering in two-dimensional (2D) electrocatalysts, and show potential for future scaling through automated slicing and transfer processes.