Reducing sizes of precious metals and utilization of the mixed small clusters of them as catalysts in reactions are important methods due to more active sites for higher catalytic efficiency.Based on first-principles calculations in this work,we found that the platinum-based clusters of Pt3X (X=Al,Si,Cu) which have the magic number 4 can effectively catalyze the water decomposition and hydrogen production in just one-step reaction process.The adsorbates of the H2O@Pt3X clusters have strong absorption in the ultraviolet and visible regions with wavelength from 300 nm to 760 nm,indicating the sunlight can be used to drive catalytic hydrolysis for producing clean hydrogen.In addition,the O atom remains on the clusters after hydrolysis and can react with CO to form CO2 in activation barrier of 0.34-0.58 eV,showing the recycling ability of the products after hydrolysis for eliminating the poisoning CO by oxidation.Moreover,the formed CO2 molecule can be detached from the Pt3X clusters at 323 K.Our results provide interesting guidance for practical designing the useful photocatalysts.