Nature Catalysis, Published online: 24 August 2026; doi:10.1038/s41929-026-01610-y A method is developed for the operando imaging of individual electrocatalytic turnovers at subparticle resolution — DELINE. Applied to surface water dissociation, this approach reveals nanoscale kinetic heterogeneity and a compensation relationship between the exchange velocity and charge transfer coefficient, providing insight for rational electrocatalyst design.