requires huge and expensive infrastructures to bear the harsh operating conditions, which further raises the production cost. [5] Thus, the development of energy efficient and environmental-friendly technologies for NH 3 synthesis is urgently important. Electrochemical methods powered by renewable electricity offer economical and environmentally friendly routes to produce NH 3 at room temperature. [6] Recently, electrochemical N 2 reduction reaction (NRR) under ambient conditions has been considered as a clean energy route for NH 3 production. [7] However, current NRR processes are still very inefficient, because of the extremely stable NN triple bond in N 2 (941 kJ mol −1 ), limited solubility of N 2 in the aqueous solution, and competing hydrogen evolution reaction (HER) in the aqueous electrolyte. [8] Thus, the practical application of NRR for NH 3 synthesis still has a long way to go. Recently, electrochemical nitrate (NO 3 − ) reduction reaction (NitRR) under ambient conditions has emerged as a highly promising strategy toward green NH 3 synthesis because the dissociation energy of N = O in NO 3 − (204 kJ mol −1 ) is much lower than that of the NN bond, which achieves much higher reaction rate for NH 3 production. [9] In addition, NO 3 −
Synthesis of polyhedral oligomeric silsesquioxanes (POSS) by the hydrolytic condensation reaction of trifunctional organosilanes [e.g., RSiCl 3 or RSi(OR) 3 ] may have achieved success. However, the exact formation mechanism of POSS, especially, an evolution process in the reaction still remains unclear. In this work, a real-time FTIR was carried out to trace the synthesis process of POSS. It was found that linear siloxanes, cyclic siloxanes, and cage-like polysiloxanes were formed during the reaction. With the help of generalized two-dimensional (2D) correlation analysis, we obtained exact sequential change among the three siolxanes, with the linear silicons formed initially. Following this was the emergence of cyclic silox-anes, and finally the cage-like polysiloxanes. Consequently, we not only proved the existence of the linear and cyclic siloxanes but also accurately detected the sequential change of the siloxanes in the process, which exhibited an intact and visual evolution process of POSS formation. Based on this, the reaction mechanism is presented. Finally, the chemical structure of cage-like products was further characterized by 29 Si-NMR and GPC measurements.
Electrocatalytic
nitrogen reduction reaction (NRR) at ambient conditions
is a promising route for ammonia (NH3) synthesis but still
suffers from low activity and selectivity. Here, ultrafine Sn nanoparticles
(NPs) grown on carbon blacks (SnSC/C) have been synthesized
through a wet-chemical method using sodium citrate dehydrate as a
stabilizing agent. Benefiting from the small sizes of Sn NPs, the
SnSC/C catalyst exhibits excellent electrocatalytic performance for NRR with
a high Faradaic efficiency of 22.76% and an NH3 yield rate
of 17.28 μg h–1 mg–1 in
the 0.1 M Na2SO4 electrolyte, outperforming
many reported electrocatalysts for NRR under similar conditions. Density
functional theory calculation results reveal that the potential-determining
step on Sn NPs is the generation of NHNH* through simultaneous hydrogenation
of N2
* by a
H* and a H+/e– pair via Langmuir–Hinshelwood
plus Eley–Rideal mechanisms.
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