Biographite from Wood—Surpassing Structural Limitations by Catalytic Graphitization Using Iron Sulfate Salts

Biomass serves as an abundant carbon feedstock, yet its inherently “non-graphitizable” nature typically limits its use in high-performance applications such as batteries and electronics. This study investigates the catalytic graphitization of wood dust using iron(II) sulfate (IS) and ammonium-iron(II) sulfate (AIS) as scalable, non-toxic alternatives to traditional metal catalysts such as Ni, Co or Mo. Wood powder was impregnated with aqueous solutions of these Fe salts and carbonized at temperatures ranging from 900 °C to 2200 °C, followed by structural and electrical characterization using XRD, Raman spectroscopy, gas adsorption, and four-point probe resistance measurements. Results demonstrate that both Fe salts successfully induced high-order graphitic regions at temperatures as low as 1100 °C, achieving interlayer spacing (~0.336 nm) close to perfect graphite, while non-impregnated wood remained poorly ordered even at 2200 °C with interlayer spacing that can be associated with turbostratic structures. This improved structural ordering is also reflected in the electrical conductivity of the catalytically graphitized samples, which is competitive with commercial graphite already at production temperatures as low as 1300 °C. Additionally, in the medium temperature range around 1500 °C, the catalytically graphitized samples show unique combinations of high conductivity and large specific surface area (up to 586 m2 g−1). These findings show that iron salts are effective, sustainable catalysts for transforming biomass into high-quality graphitic carbon at significantly reduced process temperatures.