Solid-phase production of Co–N–C electrocatalysts at a kilogram scale via the Kirkendall effect for proton exchange membrane fuel cells

Abstract

Platinum-group metal-free single-atom catalysts (SACs) are vital for cost-effective fuel cells, yet their adoption is hindered by performance limitations and challenges in scalable production. While Fe–N–C SACs offer high activity, their stability is severely compromised by Fenton-induced degradation. To address this, Co–N–C SACs have emerged as promising alternatives due to their much lower Fenton activity and hence improved durability. However, conventional synthesis relies on solvent-intensive methods, limiting large-scale, environmentally friendly production and precise structural control. Here, we report a solid-phase synthesis strategy via the Kirkendall effect for the kilogram-scale production of Co-doped zeolitic imidazolate framework-8 (Co-ZIF-8) with high reproducibility and precise compositional control. Further pyrolysis at high temperatures enables the formation of structurally well-defined Co–N–C SACs with tunable composition, high site density, and superior scalability. The optimized catalyst, when integrated as the cathode in a representative proton exchange membrane fuel cell (PEMFC) system, delivers remarkable power densities of 0.70 W cm⁻² and 0.39 W cm⁻² in O₂ and air conditions, respectively, outperforming most reported Co-based catalysts. This work establishes a generalizable and environmentally sustainable route for the large-scale production of high-performance non-precious metal electrocatalysts, advancing PEMFC technology and broader electrochemical energy applications.