Plasma Sheath Effects on Reactivity and Selectivity in Nonthermal Plasma Catalysis

Nonthermal plasma catalysis can activate kinetically challenging reactions under mild conditions, yet the role of the plasma sheath, which governs energy partitioning and charged-species delivery at the plasma-catalyst interface, remains poorly resolved. Here we quantify sheath dynamics in dielectric barrier discharge under sinusoidal (SIN) and pulsed (PUL) excitation and evaluate their influence across three representative chemistries, i.e., carbon dioxide (CO2) methanation, ammonia synthesis, and CO2 hydrogenation to methanol. PUL generates thinner, higher-field sheaths and delivers substantially improved performance. For example, in CO2 methanation, we achieved 70% CO2 conversion and 97% CH4 selectivity with an energy yield 259 g CH4 kWh‒1. A time-stepping Monte Carlo particle-tracking model reveals that PUL sheath fields sharply increase directed ion flux to the surface (e.g., H+ adsorption 26% under SIN vs 92% under PUL), rationalizing the rate enhancement. In-situ DRIFTS-MS then links sheath thinning to pathway selection: besides the formate route, PUL activates the reverse water–gas shift with subsequent CO hydrogenation toward methanation, increases NH2 throughput in NH3 synthesis, and promotes a CO-mediated route in CH3OH formation. Density functional theory with applied electric fields demonstrates that stronger sheath fields enhance adsorbate charge transfer, strengthen CO2/H binding, lower hydrogenation barriers, and suppress CO desorption, thereby enabling dual-pathway kinetics. Collectively, these results establish sheath dynamics as a tuneable physicochemical descriptor linking plasma behavior to catalytic function, providing a mechanistic foundation for the design of higher-efficiency plasma reactors and catalyst architectures.