Introduction Hydrogen peroxide (H2O2) is an important chemical that can be utilized as oxidant and fuel. Photocatalytic technology based on semiconductors can produce H2O2 from water and oxygen with sustainable solar energy as a sole energy input, which is a promising approach for industrial application. Nevertheless, the photoactivity of the common catalysts (i.e., graphitic carbon nitride, metal oxide, metal-organic frameworks, etc.) is low due to the poor utilization of solar light, easy recombination of electron-hole pairs, small quantity of reactive sites and weak redox ability. Developing efficient photocatalytic systems thus becomes an urgent target. Metal sulfides can be classified to single metal sulfide (i.e., CdS, In2S3, etc.), bimetallic sulfide (i.e., ZnIn2S4、CdIn2S4, etc.) and trimetallic sulfide (i.e., Cu2ZnSnS4). Sulfides exhibits the suitable band structures that can harness visible light and possess the proper redox capability. Meanwhile, the high structural symmetry enables them ultrafast charge carries transportation. The band structure of the semiconductor is a prerequisite both for optical absorption and redox ability. For photocatalytic H2O2 production, oxygen reduction reaction (ORR) and water oxidation reaction (WOR) channels can synergistically achieve the maximum activity. The ORR requires a potential that is more negative than -0.33 V vs. normal hydrogen electrode (NHE). The WOR needs a potential that is more positive than +1.78 V vs. NHE. The larger bandgap can induce the limited photon absorption. Thus, modulating the band structure of the metal sulfide through changing the metals ratio is an effective strategy to boost the photoactivity. Methods InxSn5-xS8 samples were prepared through a hydrothermal approach. A certain amount of InCl3·4H2O and SnCl4·5H2O were dissolved into deionized water and then added L-Cysteine into the solution. Thereafter, the suspension was treated by a hydrothermal method at 180 ℃ for 24 h. In2S3 and SnS2 were prepared by the same procedure without the addition of SnCl4·5H2O or InCl3·4H2O. The XRD patterns were characterized by X'Pert3MRD. The Raman spectra were obtained by LabRAM HR Evolution with 532 nm laser. The morphology structure was detected by a modelGemini SEM 500 scanning electron microscope and a modelJEM-2100 transmission electron microscope. The specific surface area and pore size were analyzed by a model ASAP2460BET instrument. The XPS spectra were obtained by an X-ray photoemission spectroscope with Al Kα excitation. The ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS) was determined by an ultraviolet-visible absorbance spectroscope. The photoluminescence (PL) and time-resolved photoluminescence (TR-PL) spectra were collected on Horiba Fluorologat 375 nm. The transient photocurrent, electrochemical impedance spectra and Mott-Schottky plots were measured on a modelDH7000 electrochemical workstation. Photocatalytic H2O2 production was evaluated in a sealed three-neck round bottom flask with the mixture of deionized water and isopropanol under visible light illumination (λ≥420 nm). After purging with oxygen for 30 min, the reaction system was placed under Xenon lamp and then extracted the suspension at certain time interval. The concentration of H2O2 was estimated by iodometry methods. The reaction pathway was investigated by scavengers experiment and changing the gases. Results and discussion The as-prepared In4SnS8 nanomaterials have a typical cubic structure with the flower-like morphology that is composed of ultrathin 2D nanosheets with the thicknesses of 5-10 nm. Apristine In2S3 presents a 3D solid sphere with the diameters of 4-7 μm, and SnS2 has a plate-like structure with a lateral size of ~1 μm. The hierarchical structure of In4SnS8 endow it with the maximum specific surface area of 648.056 m2/g, benefiting for the surface photoreaction. Nevertheless, pure In2S3 and SnS2 possess the small specific surface area of 70.631 m2/g and 30.411 m2/g. According the UV-Vis DRS, the bandgap of In2S3, In9SnS16, In4SnS8, In3Sn2S8, In2Sn3S8 and SnS2 is 2.03, 1.98, 2.16, 1.87, 1.80 and 1.78 eV, respectively. According to Mott-Schottky (MS) plots, their conductive band (CB) potential is calculated to be -0.24、-0.26、-0.39、-0.24、-0.22 and -0.31 eV, respectively. Their corresponding valance band (VB) is thus 1.79、1.72、1.77、1.63、1.58 and 1.47 eV, respectively. CB and VB both for In4SnS8 can meet the requirement of ORR and WOR channels for H2O2 evolution. While other photocatalysts can only undergo the single pathway of direct two-electron reduction reaction. Under visible light illumination, In4SnS8 nanomaterials have the maximum photoactivity with a H2O2 production rate of 1.936 μmol·L-1·min-1, which is 5.2- and 71.7- fold greater than that of pristine In2S3 and SnS2. They also present a good stability after 4 cycles experiments. The photo-reactivity of In9SnS16, In3Sn2S8 and In2Sn3S8 dramatically decreases in N2 atmosphere, indicating that ORR is a dominant pathway in the three systems above. For In2S3 and In4SnS8, the concentration of H2O2 is decreased by 30%-50% in N2, implying that WOR pathway is also responsible for H2O2 evolution. The trapping agent experiment demonstrates that 2e- WOR, direct one-step two-electron ORR and indirect sequential two-step single-electron ORR all exist in In4SnS8 system. Among all the photocatalysts, In4SnS8 exhibits the maximum photocurrent of 0.25 mA-cm-2, the minimum interfacial electron transfer resistance, the lowest photoluminescence signal and the shortest charge carrier lifetime, indicating that the electron-hole pairs in In4SnS8 can efficiently separate and migrate to the surface, then boost the photo-reactivity. Conclusions A series of InxSn5-xS8 materials were prepared through a hydrothermal process. In4SnS8 nanomaterials exhibited the superior photocatalytic performance and its visible-light-driven H2O2 production rate was 1.936 μmol·L-1·min-1, which was 5.2- and 71.7- fold greater than that of pristine In2S3 and SnS2. The band structure analysis demonstratedthat the bandgap and band position of InxSn5-xS8 could be controlled by In/Sn molar ratio. In4SnS8 had the proper bandgap of 2.16 eV and its CB and VB lied at -0.39 and 1.77 eV, thus satisfying the potential of two independent pathways for H2O2 generation, i.e., oxygen reduction reaction and water oxidation reaction. In addition, the hierarchical nanoflower-like structure of bimetallic In4SnS8 nanomaterials could also provide the more reactive sites, which were responsible for the improved photocatalytic performance.