Synergy of Bi2 O3 and RuO2 Nanocatalysts for Low-Overpotential and Wide pH-Window Electrochemical Ammonia Synthesis.

Electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions is still seriously impeded by the inferior NH3 yield and low Faradaic efficiency, especially at low overpotentials. Herein, we report the synthesis of nano-sized RuO2 and Bi2 O3 particles grown on functionalized exfoliated graphene (FEG) through in situ electrodeposition, denoted as RuO2 -Bi2 O3 /FEG. The prepared self-supporting RuO2 -Bi2 O3 /FEG hybrid with a Bi mass loading of 0.70 wt% and Ru mass loading of 0.04 wt% shows excellent NRR performance at low overpotentials in acidic, neutral and alkaline electrolytes. It achieves a large NH3 yield of 4.58±0.16 µgNH3 h-1  cm-2 with a high Faradaic efficiency of 14.6 % at -0.2 V versus reversible hydrogen electrode in 0.1 M Na2 SO4 electrolyte. This performance benefits from the synergistic effect between Bi2 O3 and RuO2 which respectively have a fairly strong interaction of Bi 6p orbitals with the N 2p band and abundant supply of *H, as well as the binder-free characteristic and the convenient electron transfer via graphene nanosheets. This work highlights a new electrocatalyst design strategy that combines transition and main-group metal elements, which may provide some inspirations for designing low-cost and high-performance NRR electrocatalysts in the future.

Ultrathin 1T-MoS2 Nanoplates Induced by Quaternary Ammonium-Type Ionic Liquids on Polypyrrole/Graphene Oxide Nanosheets and Its Irreversible Crystal Phase Transition During Electrocatalytic Nitrogen Reduction.

Ultrathin nanoplates of metastable 1T-MoS2 have been successfully stabilized and uniformly distributed on the surface of n-butyl triethyl ammonium bromide functionalized polypyrrole/graphene oxide (BTAB/PPy/GO) by a very simple hydrothermal method. BTAB as a typical kind of quaternary ammonium-type ionic liquids (ILs) played a crucial role in the formation of the obtained 1T-MoS2/BTAB/PPy/GO. It was covalently linked with PPy/GO and arranged in a highly ordered order at the solid-liquid interface of PPy/GO and H2O due to Coulombic interactions and other intermolecular interactions, which would induce and stabilize ultrathin 1T-MoS2 nanoplates by morphosynthesis. The good electrocatalytic activity toward nitrogen reduction reaction (NRR) with strong durability and good stability can be achieved by 1T-MoS2/BTAB/PPy/GO due to their excellent inorganic/organic hierarchical lamellar micro-/nanostructures. Especially, after the long-term electrocatalysis for NRR at a negative potential, metastable 1T-MoS2 as the catalytic center undergoes two types of irreversible crystal phase transition, which was converted to 1T'-MoS2 and Mo2N, caused by the competitive hydrogen evolution reaction (HER) process and the electrochemical reaction between the electroactive 1T-MoS2 and N2, respectively. The new N-Mo bonding prevents Mo atoms from binding to other N atoms in N2, resulting in the deactivation of the electrocatalysts to NRR after being used for 18 h. Even so, quaternary ammonium-type ILs would induce the crystal structures of transition-metal dichalcogenides (TMDCs), which might provide a new thought for the reasonable design of electrocatalysts based on TMDCs for electrocatalysis.

Bismuth-Based Free-Standing Electrodes for Ambient-Condition Ammonia Production in Neutral Media.

Electrocatalytic nitrogen reduction reaction is a carbon-free and energy-saving strategy for efficient synthesis of ammonia under ambient conditions. Here, we report the synthesis of nanosized Bi2O3 particles grown on functionalized exfoliated graphene (Bi2O3/FEG) via a facile electrochemical deposition method. The obtained free-standing Bi2O3/FEG achieves a high Faradaic efficiency of 11.2% and a large NH3 yield of 4.21 ± 0.14 [Formula: see text] h-1 cm-2 at - 0.5 V versus reversible hydrogen electrode in 0.1 M Na2SO4, better than that in the strong acidic and basic media. Benefiting from its strong interaction of Bi 6p band with the N 2p orbitals, binder-free characteristic, and facile electron transfer, Bi2O3/FEG achieves superior catalytic performance and excellent long-term stability as compared with most of the previous reported catalysts. This study is significant to design low-cost, high-efficient Bi-based electrocatalysts for electrochemical ammonia synthesis.