Preparation of corn straw-based carbon by “carbonization-KOH activation” two-step method: Gas–solid product characteristics, activation mechanism and hydrogen storage potential

Making excellent carbon-based hydrogen adsorbents requires thoroughly understanding the two-step activation method's reaction mechanism. This research examined the properties of gases and solids with high KOH/biochar ratios (4:1), various carbonization temperatures (400–600 °C), and activation temperatures (700–900 °C). The potential of biochar for hydrogen storage was further examined. These results demonstrate the division of the KOH activation process into four temperature-dependent reaction stages. The emission of CH₄, CO, and H₂ in various temperature ranges can be significantly influenced by the degree of carbonization and activation temperature. The outcome of activation is primarily determined by the volatile content and reactivity of carbon precursors. Biochar produced at 400 °C for carbonization and 900 °C for activation has a specific surface area (SSA) of 3567.33 m²/g. The oxygen concentration of H-400 decreases as the activation temperature rises, whereas the oxygen-containing structure can be built by raising the carbonization level. The hydrogen storage capacity of biochar was 2.49 wt.% at −196 °C and 1 bar, and increased to 5.51 wt.% at 50 bar, while it is 0.43 wt.% at 50 bar and room temperature. These findings can provide a novel strategy for developing carbon-based hydrogen storage materials.