An integrated gradually thinning and dual-ion co-substitution strategy modulated In-O-ultrathin-SnS2 nanosheets to achieve efficient electrochemical reduction of CO2

• Two-step gradually thinning method realizes the evolution from bulk to ultrathin. • Dual-ion co-substitution strategy improves the CO 2 RR activity of In-O-ultrathin-SnS 2 . • In-O-ultrathin-SnS 2 shows an excellent formate Faraday efficiency of 88.6%. • Oxidized Sn combined with adjacent In sites synergistically improves performance. The unique two-dimensional structure of ultrathin nanomaterials provides an ideal platform for regulating properties at the atomic level. Herein, gradually thinning method combined with dual-ion co-substitution strategy realizes the evolution of micron-sized bulk ZnSn(OH) 6 -precursor (2 μm) to functionalized In-O-ultrathin-SnS 2 nanosheets (3 nm). The In-O-ultrathin-SnS 2 achieves formate Faraday efficiency (FE HCOO -) of 88.6% and partial current density ( j HCOO -) of 22.7 mA cm −2 at a moderate overpotential of 1.0 V for CO 2 electrocatalytic reduction, which demonstrates a remarkable improvement in comparing with that of the unadorned ultrathin-SnS 2 (FE HCOO - = 17.5%, j HCOO - = 9.4 mA cm −2 ). Density functional theory calculations demonstrate that the superior activity of In-O-ultrathin-SnS 2 is attributed to the synergistic effect among oxidized Sn and the adjacent In sites in reducing the free energy of the key intermediates formation and accelerating the charge transfer rate.