Characterising a cleaner way to produce ammonia


Ammonia (NH3), a widely used chemical, is also a critical substance for producing nitrogen-containing fertilizers. Photoelectrochemical nitrogen reduction reaction (PEC NRR) is a way to synthesize it in a solar-powered green and sustainable way – it is estimated that the commonly used synthesis procedure is responsible of about 2% of the world’s energy consumption and 1.5% of total global CO2 emissions, scientists are searching for new solutions that can enhance this method (i.e. changing used photocathodes and/or electrolyte).

Schematic representation of the completely enhanced mechanism of Li-mediated PEC NRR system by optimizing the process of Li cycle [from Advanced Materials, Volume: 35, Issue: 21, First published: 11 March 2023, DOI: 10.1002/adma.202211894]
A promising way is electrochemical Lithium (Li)-mediated NRR, a process that could reduce needed external energy. However, this procedure is rarely studied and there is no fundamental understanding of its catalytic mechanism, so that its improvement is challenging. Dr Xiaoran Zhang (Hunan University), Dr Nataliya Tsud (Charles UniversityPrague) and colleagues have shown the Li-mediated PEC NRR by using silicon (Si)-based photocathodes in a lithium perchlorate (used for its high stability, safety and free labile N-containing group)-propylene carbonate solution to obtain a high NH3 yield rate and excellent faradaic efficiency.
Moreover, researchers used field emission scanning electron microscopy (FESEM) to reveal the architecture of the Si-based photocathode, and performed synchrotron radiation X-ray photoelectron spectroscopy at the Charles University Prague Materials Science Beamline (MSB) at Elettra Sincrotrone Trieste to probe changes in the chemical state and electron structure of the photocathode surface in the dark and under illumination.

For the first time, through comprehensive operando characterization, the research group gained a detailed description of the Li-mediated PEC NRR process using a Si-based photocathode, providing a novel approach for fast, cost-effective, and efficient green synthesis of NH3.



Photoelectrochemical N2-to-NH3 Fixation with High Efficiency and Rates via Optimized Si-Based System at Positive Potential versus Li0/+
Zhang X., Lyu Y., Zhou H., Zheng J., Huang A., Ding J., Xie C., De Marco R., Tsud N., Kalinovych V., Jiang S.P., Dai L., Wang S., Advanced Materials, 2023.

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