Gd-doped CuBi₂O₄/CuO heterojunction film photocathodes for photoelectrochemical H₂O₂ production through oxygen reduction

Photoelectrochemical oxygen reduction reaction (ORR) toward H₂O₂ is highly desirable because only sunlight, O₂ and water are required in the process. However, the corresponding studies are still at its infancy because of the lack of suitable photocathodes, especially inorganic semiconductor photocathodes. In this work, we report CuBi₂O₄/CuO (CBO/CuO) heterojunction submicrocrystalline film photocathodes with efficient ORR activity for H₂O₂ production. The heterojunction film photocathodes were prepared through thermal evaporation of Cu and Bi metals under vacuum and subsequent annealing treatment. Furthermore, the doping of Gd³⁺ ions into CBO/CuO could significantly enhance the yield of H₂O₂. As a result, the concentration of H₂O₂ could reach 1.3 mM within 30 min, which is 6 times higher than that obtained on the pristine CBO/CuO photocathode. The theoretical calculations suggested that the introduction of Gd could adjust the electronic structure of CBO surface and promote 2e ORR pathway for selective production of H₂O₂. Our work not only provides a new strategy for designing highly efficient photocathode for H₂O₂ production but also will evoke more interest in photoelectrocatalytic ORR through inorganic semiconductor photocathode.