Samay Garg

Converting CO2 into value-added carbon nanomaterials offers a compelling strategy for long-term carbon sequestration by generating commercially valuable products. Here, we demonstrate tandem plasma–thermocatalytic reactors for the coconversion of CO2 and C2H6 into carbon nanotubes (CNTs) and carbon nanofibers (CNFs). A dielectric barrier discharge plasma reactor activates a C2H6/CO2 feed mixture, generating reactive intermediates that serve as precursors for downstream thermocatalytic production of CNT over Co/Al2O3 at 750 °C and CNF over Co12K5/CeO2 at 450 °C. Systematic variation of plasma power and thermocatalytic reactor zone length reveals that these parameters strongly influence reactant conversion, product distribution, and carbon weight gain, enabling independent optimization of the plasma activation and thermocatalytic carbon growth. The tandem configuration enables CNT and CNF synthesis at lower temperatures than conventional chemical vapor deposition processes. An energy and CO2 footprint analysis demonstrates that, when powered by renewable electricity, the plasma–thermocatalytic system offers a modular, electrified pathway for carbon-negative sequestration. These results establish tandem plasma–thermocatalytic reactors as a flexible platform for reacting CO2 with light alkanes to produce carbon nanomaterials.

With a growing demand for electricity, clean hydrogen production and usage can be an asset not only to mitigate emissions but for long-term energy storage as well. Hydrogen gas, a high-density energy carrier, can be made through electrolysis in charging mode and generate electricity via a fuel cell in discharging mode in a unitized regenerative fuel cell (URFC). While URFCs reduce cost by combining the charging and discharging modes into a singular device, switching between modes becomes burdensome, and water management is a major challenge. One way to mitigate these issues is to operate the entire system in the vapor phase. Vapor-phase operation simplifies the physics of the system but will introduce losses within the system, primarily ohmic and mass transport during the charging mode. In this study, we explore the performance of a Proton-Exchange-Membrane (PEM)-URFC under vapor-phase conditions and the impact of different PEMs, feed gases, and relative humidity on the performance and durability. By tailoring operating conditions and membrane, the vapor-URFC achieves a roundtrip efficiency of 42% and a lifetime of 50,000 accelerated stress test cycles for fully humidified feeds. Discussion of vapor-URFC for energy storage and extensions to look at various applications shows the promise of this technology.