Shuai Zhang

CO2 conversion was investigated in a 13.56 MHz radio frequency inductively coupled plasma (RF-ICP) operated at 5–40 Pa, with emphasis on electron kinetics and dissociation pathways. The effects of coil turns and applied power were systematically evaluated using V–I measurements, Langmuir probe diagnostics, and optical emission spectroscopy. The optimized three-turn planar coil achieved a peak power-transfer efficiency of 66.9% and a maximum CO2 conversion of 37.1%. Electron density exhibited a non-monotonic pressure dependence, peaking at approximately 10–15 Pa. At lower pressure, reduced collisionality limited electron-impact reaction rates, whereas at higher pressure, decreases in electron temperature and density suppressed electron-impact dissociation and ionization. A two-dimensional fluid-chemistry model reproduced the experimentally observed conversion trend and revealed a pressure-induced shift in the dominant dissociation pathway. The ionization–recombination pathway contributed strongly at ≤15 Pa, whereas direct electron-impact dissociation became dominant above 15 Pa as the ionization pathway weakened. These results establish an experimentally anchored framework for low-pressure RF-ICP CO2 conversion and provide a mechanistic basis for future extension and validation under higher-pressure conditions relevant to Mars ISRU.

Plasma technologies convert electrical power into energetic electrons, ions, reactive species, radiation and heat, thereby breaking through the bottleneck of purely thermal or chemical routes and bringing impressive changes to our world. This roadmap reviews the progress and challenges of plasma technologies from a large‐scale and application‐driven perspective. It covers plasma–material interaction (i.e., surface modification, material preparation and semiconductor processing), aerospace applications (i.e., plasma propulsion, plasma‐assisted aerodynamics, plasma‐assisted ignition and combustion), applications in the energy field (i.e., industrial arc discharge, plasma catalysis for decarbonisation including CO ₂ conversion, nitrogen fixation and hydrogen‐related processes, and plasma‐enabled resource recovery) and applications related to human health (i.e., biomedicine, plasma disinfection/sterilisation, agriculture and food). We also present a unified cross‐comparison of mainstream plasma sources and practical selection guidelines. Beyond reviewing these advances, this roadmap argues that the large‐scale deployment of plasma technologies will be governed by four constraints: controllability of plasma parameters and discharge modes during scale‐up, system‐level energy efficiency from grid to outcome, long‐term reliability and maintainability in realistic environments, and outcome‐relevant diagnostics and harmonised benchmarking. The authors hope this roadmap will enrich the track record and enable cutting‐edge advances in plasma technologies over the next 5–10 years.

This review prensents plasma–electrocatalytic tandem ammonia synthesis, covering nitrogen activation, NO _x management, NH ₃ formation, reactor integration, and pathways toward scalable green ammonia.

Electrochemical nitrogen reduction under ambient conditions is constrained by the kinetic inertness of N₂ and competition from the hydrogen evolution reaction. Here, we report an integrated plasma-electrolysis membrane-electrode assembly that couples a microstructured nonthermal surface discharge directly to a gas-diffusion cathode, enabling in situ generation and delivery of vibrationally excited N₂, N₂(ν), to the electrocatalytic interface. Among 14 metal catalysts screened, Ag provided the best balance of activity and selectivity, achieving an NH₃ production rate of 7.7 ± 0.8 nmol s^-1 cm^-2 with an electrochemical Faradaic efficiency of 86 ± 14% at -0.54 V versus RHE under atmospheric pressure and room temperature. Plasma/electrolysis on-off controls and ¹⁵N₂ isotope-labeling experiments establish that NH₃ formation requires simultaneous plasma activation and electrochemical polarization and originates from the supplied N₂. Plasma-kinetic modeling indicates strong vibrational excitation in the discharge, with a calculated effective vibrational temperature of approximately 4300 K and 11.8% of N₂ occupying levels (ν = 4-8). Transport modeling further suggests that these comparatively long-lived excited states persist to the membrane-catalyst region. In situ Raman spectroscopy reveals N-N-containing surface intermediates only during coupled operation, while density functional theory shows that vibrational excitation lowers the free-energy requirement for the initial hydrogenation of N₂ to *NNH and shifts the rate-determining step in a catalyst-dependent manner. These findings establish vibrational-state engineering as a strategy for coupling non-equilibrium molecular activation with electrocatalysis for distributed ammonia synthesis under ambient conditions.

The electrocatalytic reduction of nitrogen oxides (NOx) to ammonia represents a promising alternative to direct N2 reduction but is often limited by low reaction rates, poor selectivity, and severe competition from hydrogen evolution under dilute feed conditions. Here, we report a plasma-enabled electrocatalytic strategy for efficient NOx-to-NH3 conversion using an electronically engineered Cu-N-P catalyst. A rotating gliding arc plasma converts air into reactive NOx species, providing a continuous and controllable feed for downstream electrochemical reduction. The Cu-N-P catalyst achieves an ammonia production rate of 2.36 mmol h−1 cm−2 with nearly 100% Faradaic efficiency at −0.575 V versus RHE and maintains stable operation for over 125 h under plasma-derived NOx conditions. Compared with unmodified Cu, the N, P co-doped catalyst promotes selective NOx adsorption and accelerates the hydrogenation of key intermediates while suppressing parasitic hydrogen evolution. Spectroscopic characterizations and theoretical analysis reveal that electronic structure modulation facilitates efficient NOx utilization and favorable hydrogenation kinetics. This work establishes an effective catalytic pathway for NOx-to-ammonia conversion under plasma-assisted conditions, providing insights into catalyst design for coupled plasma-electrochemical nitrogen conversion systems.

The in-situ resource utilization (ISRU) of the CO2 -rich Martian atmosphere is crucial for supporting future human exploration and sustained presence on Mars. This work demonstrates the application of a direct current (DC) glow discharge plasma for the direct dissociation of CO2 into O2 under simulated Martian conditions. The effects of key operational parameters including gas pressure, discharge current, and gas composition were systematically investigated in terms of discharge characteristics and CO2 dissociation performance. Results demonstrate that CO2 dissociation is highly sensitive to discharge polarity and pressure, with negative DC polarity proving particularly effective at low pressures. Optical emission spectroscopy (OES) identified distinct peaks for CO2⁺, CO, and atomic oxygen, confirming electron-impact dissociation. The addition of 10% Ar markedly intensified the CO2⁺ emission, indicative of enhanced ionization via Penning processes. In contrast, the introduction of N2 generated emission bands from excited N2 species, which promoted CO2 dissociation through energy transfer; however, this process was less efficient due to competitive energy absorption by N2 . BOLSIG+ simulations corroborated that Ar significantly increases the average electron energy and strengthens the high-energy tail of the electron energy distribution function (EEDF), thereby boosting CO2 conversion. At a specific energy input of 0.5 J•mL⁻¹, the addition of 10% Ar and 10% N2 enhanced the CO2 conversion rate by 16% and 12%, respectively. These findings provide valuable insights for developing scalable plasma-based ISRU systems for oxygen and fuel production on Mars, which are essential for future crewed missions.

To address the challenges of insulation stress on the secondary winding and low energy efficiency during the miniaturization of Tesla transformers, this article proposes a triple-resonant transformer circuit topology that incorporates a high-voltage diode. Based on the traditional dual-resonant topology, this circuit incorporates a high-voltage diode to introduce an additional self-resonance stage, thereby achieving voltage division that reduces insulation stress on the secondary winding and improves energy efficiency. A prototype of a compact 100-kV high-voltage, high-frequency nanosecond pulse generator has been developed, and by embedding the secondary high-voltage capacitor and high-voltage diode directly within the transformer, the system size is further reduced. The volume of the pulse generator is only $25\times 17\times 27$ cm (11.4 L). Detailed testing of each module showed that the pulse amplitude before sharpening reaches approximately 116 kV, which is 1.67 times the maximum voltage sustained by the Tesla secondary winding. After sharpening by a spark gap switch (SGS), a pulse with an amplitude of 100 kV, a rise time of 8 ns, and a full width at half maximum (FWHM) of 190 ns was generated across a 1.25-k $\Omega $ load. The maximum repetition rate reached 100 Hz, with a peak power density of 0.7 MW/L. This design successfully achieves the miniaturization goal while reducing insulation stress on the secondary winding by 40% and increasing efficiency to 75%.

This study establishes a plasma–electrocatalytic tandem approach that enables efficient ammonia synthesis from air and water under mild conditions with a pulsed NO _x replenishment strategy to maintain a stable concentration of intermediates.

Low-temperature plasma is widely used in thin-film deposition, circuit etching, material surface modification, and other applications in which plasma parameters can significantly affect the outcomes. Compared to single-source excitation, dual-source excitation can enhance the efficiency of energy utilization and expand the range of parameter variations. A low-pressure tube filled with a mixture of 95% Ar and 5% N₂ was developed to study the plasma properties under DC excitation and dual-source excitation with DC superimposed nanosecond pulse. The effects of different pulse amplitudes and pulse widths on the plasma properties were explored. The experimental results show that the superposition of pulses can enhance the electron density in the afterglow phase, and the enhancement of electron density in the afterglow phase is more sensitive to the pulse amplitude. The electron density can be maintained at a high level after the pulse ends, with a maximum value reaching 10¹⁷ m⁻³. In addition, the electron density in plasma under dual-source excitation can be two orders of magnitude higher than under single DC excitation, while the gas temperature decreases by approximately 40 K, thereby increasing the range of plasma parameters variations.