Structure-dependent evolution of inherent oxygen and CO₂ modulation in oxy-fuel biomass gasification: gas–solid product distribution and in-situ biochar structure

Oxy-fuel biomass gasification coupled with green hydrogen synthesis offers a promising route for utilizing surplus renewable electricity. However, existing studies focus on steam gasification for maximum hydrogen yield, overlooking CO‑selective conversion and the role of inherent oxygen. Here, corn straw and rice husk are gasified under oxy‑fuel conditions in a fluidized bed with in‑situ sampling. Increasing oxidizing intensity first raises then lowers cold gas efficiency, while higher temperature enhances carbon conversion. Introducing CO₂ increases CO yield via the Boudouard reaction, achieving optimal cold gas efficiencies of 65.8 % for corn straw at 15 % CO₂ and 68.0 % for rice husk at 10 % CO₂; excessive CO₂ inhibits O₂‑mediated oxidation. In corn straw, abundant acetyl/carboxyl groups in hemicellulose undergo decarboxylation and reforming, generating CO₂/H₂O, with residual oxygen retained as quinone‑type C=O. In rice husk, stable methoxy and β‑O‑4 aryl ether linkages in lignin favor homolytic cleavage to CO, while SiO₂ encapsulation of cellulose suppresses reactive oxygen release. Furthermore, inherent oxygen actively modulates CO₂ gasification efficiency: aliphatic C=O in corn straw promotes decarboxylation, generating competing CO₂ that reduces net CO yield from the Boudouard reaction; aromatic C–O in rice husk lignin suppresses side reactions and complements CO₂ to enhance CO production. This structure‑dependent cooperation or competition between inherent oxygen and CO₂ gasification provides a theoretical basis for the zero‑carbon route coupling oxy‑fuel biomass gasification with green hydrogen to produce green alcohols.