First-principles and experimental study of structural defects in multielement-doped biochar for enhanced H2O2 sensing

Exploiting the natural heteroatom composition of alfalfa, we synthesized a series of biochar from leaves and stems through controlled pyrolysis (300–600 ℃). Gas-sensing tests indicated that the leaf-derived material prepared at 300 ℃ (ALFLs-3) shows the highest response value to H 2 O 2 vapor among all eight materials. The enhanced gas-sensing performance is attributed to its unique wrinkled microstructure combined with heteroatoms (Ca, K, P), where ALFLs-3 generates substantial structural defects that facilitate the adsorption and activation of both O 2 and H 2 O 2 . The prepared material operates at room temperature and achieves a response of 154.99 (Δ I / I air ) to 500 ppm H 2 O 2 with rapid 21 s detection cycles, indicating certain competitiveness among room-temperature operable sensing materials. DFT calculations reveal that the co-doped system achieves well-balanced adsorption energies. The H 2 O 2 adsorption energy of −0.998 eV represents an optimal balance between high sensitivity and satisfactory reversibility, significantly stronger than those in single-element doped systems (e.g., −0.151 eV for Ca, −0.542 eV for K, and −0.081 eV for P). Meanwhile, the O 2 adsorption energy of −2.266 eV, the strongest among all configurations, facilitates efficient oxygen activation by promoting the formation of surface oxygen species. These findings clarify the origin of the improved sensing behavior. This work highlights the potential of plant organ-specific selection and low-temperature conversion strategies for transforming agricultural residues into functional gas sensing materials.