A recent review on photochemical and electrochemical nitrogen reduction to ammonia: Strategies to improve NRR selectivity and faradaic efficiency

Single and dual-atom catalysts towards electrosynthesis of ammonia and urea: a review

Ammonia and urea represent two important chemicals that have contributed to the rapid development of humanity. However, their industrial production requires harsh conditions, consuming excessive energy and resulting in significant greenhouse gas emission. Therefore, there is growing interest in the electrocatalytic synthesis of ammonia and urea as it can be carried out under ambient conditions. Recently, atomic catalysts (ACs) have gained increased attention for their superior catalytic properties, being able to outperform their micro and nano counterparts. This review examines the advantages and disadvantages of ACs and summarises the advancement of ACs in the electrocatalytic synthesis of ammonia and urea. The focus is on two types of AC - single-atom catalysts (SACs) and diatom catalysts (DACs). SACs offer various advantages, including the 100% atom utilization that allows for low material mass loading, suppression of competitive reactions such as hydrogen evolution reaction (HER), and alternative reaction pathways allowing for efficient synthesis of ammonia and urea. DACs inherit these advantages, possessing further benefits of synergistic effects between the two catalytic centers at close proximity, particularly matching the NN bond for N2 reduction and boosting C-N coupling for urea synthesis. DACs also possess the ability to break the linear scaling relation of adsorption energy of reactants and intermediates, allowing for tuning of intermediate adsorption energies. Finally, possible future research directions using ACs are proposed.

Fe─S Bond-Mediated Efficient Electron Transfer in Quantum Dots/Metal-Organic Frameworks for Boosting Photoelectrocatalytic Nitrogen Fixation

Effective electron supply to produce ammonia in photoelectrochemical nitrogen reduction reaction (PEC NRR) remains challenging due to the sluggish multiple proton-coupled electron transfer and unfavorable carrier recombination. Herein, InP quantum dots decorated with sulfur ligands (InP QDs-S2-) bound to MIL-100(Fe) as a benchmark catalyst for PEC NRR is reported. It is found that MIL-100(Fe) can combined with InP QDs-S2- via Fe─S bonds as bridge to facilitate the electron transfer by experimental results. The formation of Fe─S bonds can facilitate electron transfer from inorganic S2- ligands of InP QDs to the Fe metal sites of MIL-100(Fe) within 52 ps, ensuring a more efficient electron transfer and electron-hole separation confirmed by the time-resolved spectroscopy. More importantly, the process of photo-induced carrier transfer can be traced by in situ attenuated total reflection surface-enhanced infrared tests, certifying that the effective electron transfer can promote N≡N dissociation and N2 hydrogenation. As a result, InP QDs-S2-/MIL-100(Fe) exhibits prominent performance with an outstanding NH3 yield of 0.58 µmol cm-2 h-1 (3.09 times higher than that of MIL-100(Fe)). This work reveals an important ultrafast dynamic mechanism for PEC NRR in QDs modified metal-organic frameworks, providing a new guideline for the rational design of efficient MOFs photocathodes.