A unique electrochemical three-electrode flow-cell design is presented for in situ small-angle X-ray scattering experiments on a multi-purpose laboratory X-ray diffractometer. An electrolyte layer thickness of 2 mm enables sufficient photon transmission to acquire in situ scattering curves at high signal-to-noise ratio within less than one hour despite the restricted photon flux from a standard Cu X-ray tube. Complete tightness of the cell allows electrolyte flow with controlled gas saturation in order to guarantee constant experimental conditions even for long experimental protocols. Good electrochemical performance is achieved by a special arrangement of working and counter electrodes that are deposited on the opposing X-ray transmission windows of the cell. The functionality and reliability of the cell are demonstrated in an in situ small-angle X-ray scattering study of the degradation properties of carbon-supported Pt nanoparticles during electrochemical high-potential cycling. Careful subtraction of background scattering and absolute normalization of the scattering curves yield absolute quantitative structural information about the Pt nanoparticle phase at different stages of the degradation protocol, bringing insights into the real-time evolution during electrochemical characterization. (C) The Author(s) 2016. Published by ECS. All rights reserved.