CuPc decorating NiO for efficient photoelectrochemical ammonia production

Photoelectrochemical nitrate reduction reaction (PEC NIRR) is promising green technique to produce ammonia (NH3) as well as solve the problem of excessive nitrate (NO3−) content in wastewater, which uses clean solar energy as the main energy source. However, there are still some urgent problems to be solved in the production of NH3 by PEC NIRR. At this stage, the photocathodes cannot be in line with actual production requirements and cannot keep long-time stability. The fabrication of photocathode with good performance and high stability is the key to PEC NIRR. In this work, we successfully designed and fabricated nickel oxide/copper phthalocyanine (NiO/CuPc) heterojunctions. As a kind of metal oxide, nickel oxide (NiO) is very attractive to electrons, which provides help for the reduction reaction. At the same time, organic semiconductor CuPc could improve the utilization of visible light and the NiO/CuPc heterojunction could restrain the recombination of photogenerated electrons-holes. The heterostructure of NiO/CuPc shows excellent NH3 production ability of 9.5 μg h−1 cm−2, which has been significantly improved. Compared to pure CuPc and NiO, the NH3 yield was increased by 21.1 and 1.98 times, respectively. The accuracy of the NO3− → NH3 conversion was further valued by 15N isotope tracking. Meanwhile, NiO/CuPc sample maintains good stability in the cycle experiment. This work provides a new idea for the photoelectrochemical production of NH3.