Electrocatalysis is key to improving energy efficiency, reducing carbon emissions, and providing a sustainable way of meeting global energy needs. Therefore, elucidating electrochemical reaction mechanisms at the electrolyte/electrode interfaces is essential for developing advanced renewable energy technologies. However, the direct probing of real-time interfacial changes, i.e., the surface intermediates, chemical environment, and electronic structure, under operating conditions is challenging and necessitates the use of in situ methods. Herein, we present a new lab-based instrument commissioned to perform in situ chemical analysis at liquid/solid interfaces using ambient pressure X-ray photoelectron spectroscopy (APXPS). This setup takes advantage of a chromium source of tender X-rays and is designed to study liquid/solid interfaces by the “dip and pull” method. Each of the main components was carefully described, and the results of performance tests are presented. Using a three-electrode setup, the system can probe the intermediate species and potential shifts across the liquid electrolyte/solid electrode interface. In addition, we demonstrate how this system allows the study of interfacial changes at gas/solid interfaces using a case study: a sodium-oxygen model battery. However, the use of APXPS in electrochemical studies is still in the early stages, so we summarize the current challenges and some developmental frontiers. Despite the challenges, we expect that joint efforts to improve instruments and the electrochemical setup will enable us to obtain a better understanding of the composition-reactivity relationship at electrochemical interfaces under realistic reaction conditions.