Locking the lattice oxygen in RuO2 to stabilize highly active Ru sites in acidic water oxidation.

Ruthenium dioxide is presently the most active catalyst for the oxygen evolution reaction (OER) in acidic media but suffers from severe Ru dissolution resulting from the high covalency of Ru-O bonds triggering lattice oxygen oxidation. Here, we report an interstitial silicon-doping strategy to stabilize the highly active Ru sites of RuO2 while suppressing lattice oxygen oxidation. The representative Si-RuO2-0.1 catalyst exhibits high activity and stability in acid with a negligible degradation rate of ~52 µV h-1 in an 800 h test and an overpotential of 226 mV at 10 mA cm-2. Differential electrochemical mass spectrometry (DEMS) results demonstrate that the lattice oxygen oxidation pathway of the Si-RuO2-0.1 was suppressed by ∼95% compared to that of commercial RuO2, which is highly responsible for the extraordinary stability. This work supplied a unique mentality to guide future developments on Ru-based oxide catalysts' stability in an acidic environment.

Plasma-induced nitrogen vacancy-mediated ammonia synthesis over a VN catalyst.

Plasma catalysis has recently been recognized as a promising route for artificial N2 reduction under mild conditions. Here we report a highly active VN catalyst for plasma-catalytic NH3 synthesis via the typical Mars-van Krevelen (MvK) mechanism. Our results indicate that NH3 synthesis occurs through the continuous regeneration and elimination of nitrogen vacancies on the VN surface. With this strategy, the VN catalyst achieves a superhigh NH3 yield of 143.2 mg h-1 gcat.-1 and a competitive energy efficiency of 1.43 gNH3 kW h-1.

The role of nitrogen sources and hydrogen adsorption on the dynamic stability of Fe-N-C catalysts in oxygen reduction reaction.

Fe-N-C catalysts are promising alternatives to Pt-based electrocatalysts for the oxygen reduction reaction (ORR) in various electrochemical applications. However, their practical implementation is impeded by their instability during prolonged operation. Various degradation mechanisms have been proposed, yet the real origin of the intrinsic instability of Fe-N-C structures under ORR operations is still disputed. Herein, we observed a new type of protonation mechanism based on advanced first-principles simulations and experimental characterizations. The results revealed strong evidence of pyrrolic-N protonation in pyrrolic-type FeN4, which plays a vital role for the low kinetic barrier of Fe leaching. Conversely, the pyridinic-type FeN4 prefers protonation at the Fe site, contributing to the higher barrier of Fe leaching and relatively higher stability. The facile pyrrolic-N protonation is verified by various spectroscopy characterizations in the Nafion-treated FePc molecule. Crucially, the presence of oxygen-containing intermediates at the Fe site can further work synergistically with N protonation to promote conversion of iron atoms (Fe-N4) into ferric oxide under working potentials, and the more positive the electrode potential, the lower the kinetic barrier of Fe leaching. These findings serve as a foundation for future research endeavors on the stability issues of Fe-N-C catalysts and advancing their application in sustainable energy conversion technologies.