Photoelectrochemical reduction of nitrate to ammonia over CuPc/CeO2 heterostructure: Understanding the synergistic effect between oxygen vacancies and Ce sites

[Display omitted] •CuPc/CeO2 with rich OVs has been successfully fabricated for PEC NO3– reduction.•CuPc/CeO2 exhibited the NH3 production rate up to 1.16 μmol h-1m−2.•Thermodynamic and kinetic factors of PEC NRR have been synergistically optimized.•The isotope NMR result further confirmed the accuracy of NO3– → NH3 conversion. Photoelectrochemical nitrate (NO3–) reduction reaction (PEC NRR) is a promising technology to solve both environmental pollution and traditional energy crisis. However, the fabrication of efficient catalyst with controllable active sites for high selectivity is still challenging. In this work, copper phthalocyanine (C32H16CuN8)/cerium dioxide (CuPc/CeO2) heterostructure has been designed as a model to understand the role of Ce3+/Ce4+ pairs on the formation of oxygen vacancies (OVs), which helps for identifying the key factors to adjust the chemical adsorption and activation of NO3– in PEC NRR system. Furthermore, the unique organic–inorganic hybrid matrix significantly strengthens the relationship of solar harvest–carriers’ separation–NO3– reduction. CuPc/CeO2 heterostructure exhibits a high NH3 yield of 1.16 μmol h−1 cm−2 and Faradic efficiency of 33% (-0.6 V vs.), and the desirable PEC NRR could be well retained for 5 cycles. Therefore, the construction of CuPc/CeO2 successfully optimizes the thermodynamic and kinetic factors in PEC NRR system, providing a new insight for organic–inorganic hybridization and NH3 green production.