Methane (CH₄) and nitrogen (N₂) are abundant feedstocks whose valorization is central to addressing challenges in energy, agriculture, and the environment. However, their conversion still relies largely on centralized, carbon-intensive thermochemical processes. Developing synthetic routes under ambient conditions is therefore important for reducing greenhouse gas emissions, improving the sustainability of chemical manufacturing, and helping close anthropogenic carbon and nitrogen cycles. Yet the kinetic inertness of CH₄ and N₂ makes their selective conversion under ambient conditions difficult. Direct electrocatalysis is limited by sluggish reaction kinetics, low production rates, low Faradaic efficiencies (FE), and competing side reactions. Non-thermal plasma (NTP), which can activate inert molecules under ambient conditions, offers a distinct route to address these limitations.
In our previous work, we developed an NTP-driven N₂ oxidation route that generates NO_x species for subsequent electrochemical conversion. This strategy showed that NTP activation and electrocatalytic selectivity can be coupled to enable inert small-molecule conversion under ambient conditions ¹. However, this stable-intermediate-mediated route has intrinsic limitations, including active-species loss during long-range mass transport and low electron utilization in multi-electron transfer processes. In addition, NO_x generation and transport may introduce secondary environmental concerns and complicate downstream integration. These limitations motivate a more direct plasma–electrocatalytic strategy.
To address these challenges, we propose a plasma–electrocatalytic approach that couples micro-structured plasma discharge with a flow cell. This configuration activates inert gas-phase molecules in situ and delivers short-lived reactive species to the catalyst–electrolyte interface. As a result, the key challenge shifts from direct electrochemical activation of inert molecules to selective electrochemical conversion of plasma-generated reactive species.
We first validated this concept in CH₄-to-methanol conversion. Plasma activation of CH₄ generates methyl radicals (·CH₃), which couple with adsorbed OH at the electrocatalytic interface. The hybrid system achieved a FE above 90%, an energy yield of 60 g kWh^-1, and stable operation for 890 h ².
We then extended this strategy to N₂-to-NH₃ conversion. Using Ag as a model catalyst, we verified the delivery of excited-state N₂ to the electrocatalytic interface and its involvement in NH₃ formation. Control experiments, ¹⁵N₂ isotope-labelling, plasma kinetic modelling, in-situ Raman spectroscopy, and density functional theory (DFT) calculations confirmed that NH₃ formation results from the coupling of plasma-activated N₂ with electrochemical reduction. Building on this proof of concept, we optimized the catalyst using Ni-doped MoS₂ gas-diffusion electrodes to promote selective N–H bond formation at low potentials to improve the utilization of plasma-activated N₂ species. The 5% Ni/MoS₂ electrode achieved an NH₃ FE of 72.8 ± 2.2% and a production rate of 0.047 mmol h^-1 cm^-2 at −0.17 V vs. RHE. DFT calculations show that activated N₂ adsorbs more favorably than ground-state N₂, while Ni incorporation optimizes H adsorption and stabilizes key nitrogen-containing intermediates. Techno-economic and life-cycle analyses identify plasma energy efficiency and low-carbon electricity as key factors for economically and environmentally competitive plasma–electrochemical nitrogen reduction ³.
Overall, this study establishes plasma electrocatalysis as a radical- and excited-state-mediated platform for sustainable carbon and nitrogen conversion under ambient conditions. By utilizing short-lived reactive species at the interface, this approach enables the renewable-electricity-driven conversion of inert small molecules into transportable fuels and chemicals, offering a route toward distributed and sustainable chemical manufacturing.. 

 

plasma electrocatalysis,nitrogen fixation,methane oxidation,energy efficiency