Top-down nanostructured multilayer MoS2 with atomically sharp edges for electrochemical hydrogen evolution reaction

Abstract

Cost-efficient and readily scalable platinum-free electrocatalysts are crucial for a smooth transition to future renewable energy systems. Top-down activation of MoS₂ promises the production of sustainable hydrogen evolution electrocatalysts from the Earth-abundant molybdenite ore. Here, the deterministic nanopatterning of multilayer MoS₂ with numerous zigzag edges is explored as a pathway to enhance hydrogen evolution reaction (HER). Nanopatterned single-nanosheet MoS₂ electrodes are assessed by two highly localized electrochemical techniques: selected area voltammetry (with lithography-defined regions of electrode-electrolyte contact) and Scanning ElectroChemical Microscopy (SECM). The nanopatterning effect is the most pronounced after prolonged electrochemical cycling in an acidic electrolyte. The electrocatalytic hydrogen evolution activity of edge-enriched electrodes is dramatically enhanced: the maximum electrochemical current density (j${}_{max}$) achieved at -510 mV vs. reversible hydrogen electrode (mV${}_{RHE}$) is increased by two orders of magnitude, reaching >300 mA⋅cm⁻². Both the ${\eta }_{10}$ and ${\eta }_{100}$ overpotentials are significantly reduced as well. Meanwhile, pristine MoS₂ shows just ≈6 times j${}_{max}$ increase (≈30 mA⋅cm⁻²) after the very same cycling. The increased electrocatalytic activity comes with electrode morphology degradation, evidenced by ex-situ scanning electron microscopy. SECM directly visualizes stronger HER activity in the regions with densely located zigzag edges. Intense white light illumination significantly boosts HER on MoS₂ electrodes due to the photo-enhanced MoS₂ conductivity. These results improve the understanding and reveal the limitations of MoS₂-based electrocatalytic water splitting.