Recent progress on Janus MoSSe for photocatalytic applications.

Janus MoSSe has emerged as a promising 2D platform for photocatalytic water splitting owing to its intrinsic out-of-plane dipole, selective surface reactivity, and efficient charge separation. However, pristine MoSSe remains intrinsically limited for the oxygen evolution reaction (OER), which drives the need for structural, chemical, and interfacial engineering. In this perspective, we review recent progress in understanding how defect chemistry, transition-metal functionalization, doping, curvature, and van der Waals heterostructures alter dipole moments, band alignment, carrier lifetimes, and water adsorption energies-all key physical descriptors governing catalytic performance. An interesting picture emerges: MoSSe becomes an effective photocatalyst when paired with an OER-active partner that complements its strong HER-driving conduction band. Connecting it with 2D materials like WS2, black phosphorus, GaN, and AlN introduces the necessary valence-band depth and polarization to meet both redox requirements. The experimental MoSSe/GaN system supports the theoretical predictions and adds multifunctional Rashba-Dresselhaus spin splitting and magnetic-field-enhanced charge dynamics to the list of photocatalytic descriptors. Collectively, these insights lay out a design roadmap for engineering Janus-based heterostructures that optimize water splitting under visible light.