https://photojournal.jpl.nasa.gov/catalog/PIA24201

The engineering model (EM), an almost identical twin of MOXIE, is used for testing in the lab at NASA's Jet Propulsion Laboratory in Pasadena, California. Inside this gold-plated aluminum box is the Solid Oxide Electrolysis unit, or SOXE, the heart of MOXIE. Using an electrochemical process called electrolysis, SOXE takes in the carbon dioxide gas and splits it into carbon monoxide and oxygen, which is measured for purity, filtered, and then released back into the Mars atmosphere. Tubes to take in the Mars atmosphere and vent oxygen and carbon monoxide produced by the EM are connected at the top of the EM. The electronics needed to run this complex machine are housed inside the larger sidewall seen on the right.

NASA's Jet Propulsion Laboratory in Southern California built and will manage operations of the Mars 2020 Perseverance rover for NASA.