Cost-effective hydrotalcite-derived Fe-based catalysts for stable and continuous catalytic methane decomposition

Abstract

Catalytic methane decomposition (CMD) is a promising technology for CO₂-free hydrogen (H₂) production and valuable carbon co-product generation. However, stable and continuous CMD operation remains challenging due to rapid catalyst deactivation from carbon accumulation, necessitating further reactor design and development of cost-effective and stable catalysts. Here, we present an economic and environmentally friendly method for preparing hydrotalcite-derived Fe-based catalysts. The Fe content in the catalyst is precisely tuned by varying the molar ratio of ferrous to ferric ions, enabling systematic optimization of catalytic performance. The optimal Fe²⁺₇Al³⁺₃-O catalyst achieves a high CH₄ conversion efficiency of 63.4% and H₂ generation rate of about 30 mL g_cat.⁻¹ min⁻¹ at 1.5 h, sustaining 50% conversion over 10 h with a total carbon yield of 9.509 g_carbon g_cat.⁻¹. The lengths of the carbon products (i.e., carbon nanotubes (CNTs)) range from 0.5 to 5 µm and their diameters mainly distribute between 20 and 40 nm. Subsequent acid purification removes aggregated particles, impurities, and the residual catalyst, yielding purified carbon products with an open end side (pore diameter: 3.827 nm), improved dispersibility and suitability for battery applications. In a sodium-ion half cell with Na₂Fe(SO₄)₂ (NFS) as the cathode, the purified CNT used as a conductive additive shows lower ohmic resistance and delivers performance comparable to that of commercial CNTs, underscoring the notable electrochemical merits of our purified CNTs. This work offers solutions for both methane utilization and battery technology while bridging two crucial areas of sustainable energy research.