In a such two-stage set-up, the main role of the plasma is to alter the gas composition fed to the catalytic reactor.[29] In a PEC system, synergistic effects are greater since short-lived excited species are formed near the catalyst surface.[30] The way the catalyst is inserted in the PEC reactor influence the overall performance. It can be placed inside the reactor in different ways: in powder form (packed bed), deposited on foams, deposited on structured material (honeycomb), and coating of the reactor walls