Hydrogen peroxide (H2O2),an environmentally friendly oxidant,has already been widely used in many chemical synthesis and industrials as an altemative to replace traditional oxidants including chlorinated oxidizers and strong acids.However,the conventional synthesis method confronts intense energy cost,tedious separation procedures and high cost,which is not competitive with traditional oxidants.Although direct H2O2 synthesis from H2 and O2 is a green and atomically economic reaction,satisfactory activity and desirable selectivity still remain formidable challenges.Herein,for the first time,a class of Pd@NiO-x nanoparticles (NPs) (x =1,2,3 and 4) with a unique core@shell interface structure has been created to achieve high activity,selectivity and stability for the direct H2O2 synthesis.A precise thermal annealing on Pd@Ni-x NPs revealed that the resulting Pd@NiO-x NPs exhibited the volcano-like activity toward direct H2O2 synthesis as a function of annealing temperature and time.By tuning the composition of Pd@NiO-x NPs and the reaction condition,the efficiency of H2O2 synthesis could be well optimized with 5 wt％ Pd@NiO-3/TiO2 exhibiting the highest productivity (89 mol/(kgcat h)) and selectivity (91％) to H2O2 as well as excellent stability,making it one of the best catalysts for direct H2O2 synthesis reported to date.