Recent developments on multi- versus single-metallic catalytic graphitisation of biocarbon: A review

The typical graphitisation process involves non-renewable carbon sources and high temperatures, which lead to increased carbon dioxide emissions and energy consumption in the resulting graphite. Biocarbon derived from biomass acts as a sustainable carbon source that can be graphitised at lower temperatures with the aid of catalysts. This review highlights the significance of both multi- and single-metallic catalytic graphitisation of biocarbon. Introducing a catalyst offers an effective means to modify the graphitisation conditions and the characteristics of graphitic layers formed at the atomic and molecular levels. Multi-metal catalysts demonstrate superior effectiveness in lowering the graphitisation temperature to 800 °C compared to single-metal catalysts (1000–1800 °C) and those without catalysts (>2000 °C), where the synergistic interaction of two distinct metals enhances the transformation of amorphous carbon into graphitic biocarbon, as opposed to single-metal catalysts. This paper establishes a hierarchy of the graphitisation conditions as follows: temperature > carbon precursors > heating rate. Furthermore, this work outlines the existing knowledge gap regarding metallic catalysts and clarifies the roles of transition, alkaline, and alkaline earth metal catalysts in the graphitisation of bioresources.