Plasma-engineered ultra-low RuPt alloy loading on N-doped carbon nanotubes for efficient methanol oxidation in direct methanol fuel cells

Developing efficient and low-cost catalysts with minimal noble metal usage remains a key challenge for direct methanol fuel cells (DMFCs). Herein, we present a plasma-assisted dual-strategy that integrates direct-current plasma magnetron sputtering (DC-PMS) and radio-frequency (RF) plasma treatment to fabricate RuPt alloy nanoparticles on CoFe-embedded nitrogen-doped carbon nanotubes supported on carbon fiber cloth (p-RuPt-CoFe@NCNT/CFC). With only 0.11 wt% Ru and 0.73 wt% Pt, the catalyst achieves ultra-low platinum group metal (PGM) loading while maintaining abundant structural defects, including carbon vacancies and nitrogen dopants. These plasma-induced modifications increase the density of active sites, promote the generation of Pt⁰ and Ru⁰ species, and strengthen metal–support interactions, thereby enhancing catalytic stability and CO tolerance. With a PGM loading of only 0.35 mg cm⁻², the p-RuPt-CoFe@NCNT/CFC catalyst delivers a mass activity of 402.6 mA mg⁻¹_PGM, demonstrating competitive performance compared with recently reported low-loading PtRu catalysts. Density functional theory (DFT) calculations show that carbon defects and nitrogen dopants in NCNTs strongly promote RuPt nucleation and growth, enhance binding affinity at the metal–support interface, shift the Pt d-band center away from the Fermi level, and reduce CO adsorption energy—collectively accounting for the enhanced CO tolerance and high methanol oxidation reaction activity.