Photoelectrochemical N<sub>2</sub> -to-NH<sub>3</sub> Fixation with High Efficiency and Rates via Optimized Si-Based System at Positive Potential versus Li<sup>0/</sup>.
basic_science · Level V
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- Record sourced from PubMed, PMID 36905214.
- Also identified by DOI 10.1002/adma.202211894.
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Abstract
As a widely used commodity chemical, ammonia is critical for producing nitrogen-containing fertilizers and serving as the promising zero-carbon energy carrier. Photoelectrochemical nitrogen reduction reaction (PEC NRR) can provide a solar-powered green and sustainable route for synthesis of ammonia (NH<sub>3</sub> ). Herein, an optimum PEC system is reported with an Si-based hierarchically-structured PdCu/TiO<sub>2</sub> /Si photocathode and well-thought-out trifluoroethanol as the proton source for lithium-mediated PEC NRR, achieving a record high NH<sub>3</sub> yield of 43.09 µg cm<sup>-2</sup> h<sup>-1</sup> and an excellent faradaic efficiency of 46.15% under 0.12 MPa O<sub>2</sub> and 3.88 MPa N<sub>2</sub> at 0.07 V versus lithium(0/+) redox couple (vs Li<sup>0/+</sup> ). PEC measurements coupled with operando characterization reveal that the PdCu/TiO<sub>2</sub> /Si photocathode under N<sub>2</sub> pressures facilitate the reduction of N<sub>2</sub> to form lithium nitride (Li<sub>3</sub> N), which reacts with active protons to produce NH<sub>3</sub> while releasing the Li<sup>+</sup> to reinitiate the cycle of the PEC NRR. The Li-mediated PEC NRR process is further enhanced by introducing small amount of O<sub>2</sub> or CO<sub>2</sub> under pressure by accelerating the decomposition of Li<sub>3</sub> N. For the first time, this work provides mechanistic understanding of the lithium-mediated PEC NRR process and opens new avenues for efficient solar-powered green conversion of N<sub>2</sub> -to-NH<sub>3</sub> .