This dataset contains a comprehensive collection of electrochemical performance, characterisation, and durability datasets generated from membrane electrode assemblies (MEAs) fabricated using graded and uniform gas‑diffusion electrodes (GR1, GR2, GR3, GD4). The data include polarization curves collected at multiple relative humidities, impedance spectra measured under controlled high‑current operation, elemental distribution profiles across catalyst layers, and cyclic voltammetry and polarization measurements recorded throughout an accelerated degradation test (ADT). All experiments were carried out at 80 °C under well‑defined gas flow, humidity, and pressure conditions, following U.S. Department of Energy (DoE) protocols where applicable. The files are provided in standard numerical formats suitable for quantitative analysis and comparison across electrode structures and ageing states.The polarization curve datasets report steady‑state voltage–current behaviour at 20%, 60%, and 100% relative humidity, while the ADT‑related files capture performance loss and electrochemical surface area decay over 30,000 potential cycles. Electrochemical impedance spectroscopy (EIS) measurements at 900 mA cm⁻² provide frequency‑resolved information on charge‑transfer and transport processes at different humidity levels, and the EDS profiles quantify through‑plane ionomer and catalyst distributions in electrodes with engineered morphology. Together, these datasets offer a detailed picture of fuel‑cell performance, degradation mechanisms, and structure–property relationships across the tested MEA configurations.