Correlating the microstructure of an energy conversion device to its performance is often a complex exercise, notably in solid oxide fuel cell research. Solid oxide fuel cells combine multiple materials and interfaces that evolve in time due to high operating temperatures and reactive atmospheres. We demonstrate here that operando environmental transmission electron microscopy can identify structure-property links in such devices. By contacting a cathode-electrolyte-anode cell to a heating and biasing microelectromechanical system in a single-chamber configuration, a direct correlation is found between the environmental conditions (oxygen and hydrogen partial pressures, temperature), the cell open circuit voltage, and the microstructural evolution of the fuel cell, down to the atomic scale. The results shed important insights into the impact of the anode oxidation state and its morphology on the cell electrical properties.|By contacting a solid oxide fuel cell to a microelectromechanical system inside an environmental electron microscope, the authors establish links between environmental conditions (gas atmosphere, temperature), cell voltage and atomic-scale structure.