Alloying Pd with Ru enables electroreduction of nitrate to ammonia with ∼100% faradaic efficiency over a wide potential window.

Electrocatalytic nitrate (NO3-) reduction reaction (eNO3-RR) to ammonia under ambient conditions is deemed a sustainable route for wastewater treatment and a promising alternative to the Haber-Bosch process. However, there is still a lack of efficient electrocatalysts to achieve high NH3 production performance at wastewater-relevant low NO3- concentrations. Herein, we report a Pd74Ru26 bimetallic nanocrystal (NC) electrocatalyst capable of exhibiting an average NH3 FE of ∼100% over a wide potential window from 0.1 to -0.3 V (vs. reversible hydrogen electrode, RHE) at a low NO3- concentration of 32.3 mM. The average NH3 yield rate at -0.3 V can reach 16.20 mg h-1 cm-2. Meanwhile, Pd74Ru26 also demonstrates excellent electrocatalytic stability for over 110 h. Experimental investigations and density functional theory (DFT) calculations suggest that the electronic structure modulation between Pd and Ru favors the optimization of NO3- transport with respect to single components. Along the *NO3 reduction pathway, the synergy between Pd and Ru can also lower the energy barrier of the rate-determining steps (RDSs) on Ru and Pd, which are the protonation of *NO2 and *NO, respectively. Finally, this unique alloying design achieves a high-level dynamic equilibrium of adsorption and coupling between *H and various nitrogen intermediates during eNO3-RR.

Phase Transition Modulated by Grain Size and Lattice Distortion in Layered Transition Metal Oxide for Sodium-Ion Batteries.

Low-cost sodium-ion batteries have demonstrated great prospects in energy storage, among which layered transition metal oxides hold great potential as a cathode material. However, the notorious phase transition in layered cathode materials has greatly hampered their cycle life due to large volume changes upon desodiation/sodiation. In this study, by adopting an O3-type NaNi1/3Fe1/3Mn1/3O2 (NFM) with controlled synthesis temperatures, we have revealed that the grain size is closely related to its phase transition behaviors. The layered material with a smaller grain size and more distorted lattice tends to experience a shorter plateau of the O3-P3-O3 phase transitions during the charge/discharge process. Despite having a lower nominal discharge capacity without the phase transition plateau, its cycling stability increases from 77.4% to 96.2% after 100 cycles with greatly reduced intragranular cracks. The smaller grain size and lattice distortion act as a barrier that prevents the smooth layer from gliding upon sodium intercalation and deintercalation. This study focuses on the influence of grain size on battery cycle stability and provides a basis for future analysis of the structural instability of layered materials.