Coexisting Cu clusters and Cu–Nₓ sites in ZIF-8-derived carbon for plasma-catalytic hydrogen evolution from water vapor

Cu/Z-700 enables plasma-driven H₂ evolution from simulated seawater vapor. • Dynamic Cu redox cycling acts as an electron relay during plasma catalysis. • Cu clusters, Cu N sites, and pyridinic N perform differentiated functions. • An H₂ rate of 1.33 mL min −1 is achieved with >95% activity after five cycles. How different active sites cooperate under non-thermal plasma (NTP) conditions is still poorly understood. Here, Cu-doped ZIF-8-derived carbon carbonized at 700 °C (Cu/Z-700) is shown to host three distinct active centers: metallic Cu clusters, Cu–N coordinated (Cu–NC) moieties and pyridinic N (Py-N) sites. Cu K-edge X-ray absorption spectroscopy reveals that ~80% of Cu exists as metallic clusters and ~ 20% as isolated Cu δ+ –Nₓ sites. Density functional theory (DFT) calculations suggest a functional division among the three sites: Cu clusters show the strongest Cu–OH binding and the most favorable reaction free energies, Cu–NC sites favor intermediate conversion and product desorption, and Py-N sites promote water adsorption. In a dielectric barrier discharge (DBD), Cu/Z-700 delivers a H₂ production rate of 1.33 mL min −1 from water vapor generated from simulated seawater at a residence time of 3 s, an 11-fold enhancement over plasma alone, with 93.6% activity retention over 20 cycles. Gas-phase product analysis shows that more than 97% of the H₂ originates from water splitting. The results clarify the nature of the active sites in Cu/ZIF-8-derived carbon and their contribution to plasma-catalytic water splitting. Download: Download high-res image (169KB) Download: Download full-size image