Nature Chemistry, Published online: 10 September 2026; doi:10.1038/s41557-026-02245-z Visualizing plasmon-enhanced H2 activation and propagation on catalytic surfaces remains challenging because conventional spectroscopies lack nanoscale resolution. Now it has been shown that tip-enhanced Raman spectroscopy maps H2 activation within an Ag tip–Pt(111) nanocavity and reveals H atoms propagating hundreds of nanometres across Pt(111) through a collective crowd effect.