Heterophase hexagonal/orthorhombic molybdenum trioxide nanorods for photocatalytic hydrogen production

Phase engineering plays a critical role in enhancing photocatalytic performance of metal oxides. Herein, we demonstrate the phase-selective synthesis of MoO 3 (hexagonal h-MoO 3 , orthorhombic α-MoO 3 , and their junction h/α-MoO 3 ) through controlled phase transitions by adjusting annealing conditions. As evidenced with photocatalytic hydrogen evolution reaction, h/α-MoO 3 (14.20 μmol/h) phase junction shows superior performance to either h-MoO 3 (9.62 μmol/h) or α-MoO 3 (11.31 μmol/h), with a hydrogen yield of 47.6% and 25.6% greater than that of h-MoO 3 and α-MoO 3 (Pt as cocatalyst), respectively. A systematic study of the chemical structure characterizations, photochemical tests, band structure analysis, and photocatalytic activity evaluation reveal that, the enhancement is attributed to the strong built-in electric field in the h/α-MoO 3 phase junction, which effectively facilitates charge separation. Our findings introduce a novel strategy for improving photocatalytic performance using phase engineering.