(A) N–N distance of free N₂, N₂ on CuCr-V_O^••, N₂ on CuCr-V_O^••-Strain, N₂H₂, and N₂H₄. (B) 2D structural model of TiO₂ nanosheets with V_O^•• and engineered strain. (C) The O₂ chemisorbed at a coordinatively unsaturated W site of defective WO₃, and (D) the O₂ adsorbed at the surface of perfect WO₃. The purple and olive colors represent increase and decrease in electron density, respectively, revealed by first-principle calculations. (A) Adapted with permission from Ref. [74], copyright 2017 Wiley-VCH; (B) adapted with permission from Ref. [76], copyright 2019 Wiley-VCH; (C and D) adapted with permission from Ref. [77], copyright 2016 American Chemical Society.