A Review of Catalytic Methane Decomposition on Biochar

In the transition toward a hydrogen economy, sustainable production pathways are critical. Traditional routes suffer from high CO₂ emissions and prohibitive operational costs, driving the demand for cost-effective, low-carbon alternatives. Turquoise hydrogen, produced from the thermal decomposition of methane to hydrogen and solid carbon, offers a promising CO₂-emission-free pathway. This reaction is often assisted by catalysts, including transition metals and carbonaceous materials. Particularly, biochar, produced from the pyrolysis or gasification of biomass, has emerged as a highly tunable carbon material based on sustainable and low-cost feedstocks. However, inevitable carbon deposition on the catalyst surface causes rapid deactivation by blocking the pores and active sites. In this Review, key parameters influencing the catalytic performance of biochar for catalytic methane decomposition (CMD), including physical and chemical properties, are discussed. Furthermore, modifications of the biochar catalytic activity through physical and chemical activation and the utilization of additives such as transition metals and metal oxides have been reviewed. It was found that KOH and H₃PO₄ were the most efficient chemical activation agents in improving surface area, in some cases exceeding 1000 m²/g, and altering surface chemistry. This enabled an increase in the initial methane conversion by up to three times. Adding transition metals, such as Ni and Fe, may improve the initial methane conversion by more than 3-fold. Trends in catalytic performance were quantitatively compared through the evaluation of rate constants, obtained by kinetic analysis, and time-averaged hydrogen production rates. The results show that while carbon materials are less active than transition metals, they could be promising, low-cost, and sustainable alternatives. The comparison further reveals that the surface area, pore volume, defect density, and surface chemistry collectively influence the activity. Finally, experimental recommendations are provided on conversion calculation methods, adsorption isotherm protocols, and reactor material selection to improve comparability across studies and support the development of biochar-based CMD toward an industrial scale.