New insights into the mechanism of biomass char steam gasification process by oxygen-containing functional group as aromatic carbon boundaries: Experimental and DFT study

•The existence of OCFG promotes the production of H2.•The different substitution positions of OCFG have different effects.•Each OCFG reacts individually in the composite boundary better than together.•The H atoms in OCFG are more active than those in the aromatic boundary.•The optimal paths and rate-determining steps for each boundary are determined.