We present measurements of the nucleation, growth and evolution of single hydrogen nanobubbles containing zeptomoles of molecular hydrogen and likely originating from a single catalytic site. These bubbles are measured using nanoscale platinum and gold meniscus-contacted electrodes, whose pico-liter volumes facilitate rapid supersaturation and evolution of bubbles. Observed periodic current transients were utilized to understand the nucleation, growth, coalescence, and evolution of single nanobubbles at different overpotentials and pHs. This provides a novel platform to understand factors governing bubble nucleation and evolution. These measurements offer exciting possibilities to connect experiments with computational models in important energy applications. (C) 2018 Elsevier Ltd. All rights reserved.