HIGHLIGHTS • The Bi 2 O 3 nanoplates homogeneously decorated free-standing exfoliated graphene (Bi 2 O 3 /FEG) was prepared by a facile electrochemical deposition method. • The Bi 2 O 3 /FEG first used as nitrogen reduction electrocatalyst exhibits excellent electrocatalysis performance and stability for nitrogen reduction reaction in neutral media. • The superior electrocatalytic nitrogen reduction activity is attributed to the strong interaction of the Bi 6p band with the N 2p orbitals, binder-free nature of the electrodes, and facile electron transfer through the graphene nanosheets. ABSTRACT Electrocatalytic nitrogen reduction reaction is a carbonfree and energy-saving strategy for efficient synthesis of ammonia under ambient conditions. Here, we report the synthesis of nanosized Bi 2 O 3 particles grown on functionalized exfoliated graphene (Bi 2 O 3 /FEG) via a facile electrochemical deposition method. The obtained free-standing Bi 2 O 3 /FEG achieves a high Faradaic efficiency of 11.2% and a large NH 3 yield of 4.21 ± 0.14 μg NH 3 h −1 cm −2 at − 0.5 V versus reversible hydrogen

Ultrathin nanoplates of metastable 1T-MoS 2 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-MoS 2 /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 H 2 O due to Coulombic interactions and other intermolecular interactions, which would induce and stabilize ultrathin 1T-MoS 2 nanoplates by morphosynthesis. The good electrocatalytic activity toward nitrogen reduction reaction (NRR) with strong durability and good stability can be achieved by 1T-MoS 2 /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-MoS 2 as the catalytic center undergoes two types of irreversible crystal phase transition, which was converted to 1T′-MoS 2 and Mo 2 N, caused by the competitive hydrogen evolution reaction (HER) process and the electrochemical reaction between the electroactive 1T-MoS 2 and N 2 , respectively. The new N−Mo bonding prevents Mo atoms from binding to other N atoms in N 2 , 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. KEYWORDS: n-butyl triethyl ammonium bromide (BTAB), polypyrrole/graphene oxide (PPy/GO), 1T-MoS 2 , nitrogen reduction reaction (NRR), irreversible crystal phase transition

Electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions is still seriously impeded by the inferior NH 3 yield and low Faradaic efficiency, especially at low overpotentials. Herein, we report the synthesis of nanosized RuO 2 and Bi 2 O 3 particles grown on functionalized exfoliated graphene (FEG) through in situ electrodeposition, denoted as RuO 2 À Bi 2 O 3 /FEG. The prepared self-supporting RuO 2 À Bi 2 O 3 /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 NH 3 yield of 4.58 � 0.16 μg NH3 h À 1 cm À 2 with a high Faradaic efficiency of 14.6 % at À 0.2 V versus reversible hydrogen electrode in 0.1 M Na 2 SO 4 electrolyte. This performance benefits from the synergistic effect between Bi 2 O 3 and RuO 2 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 maingroup metal elements, which may provide some inspirations for designing low-cost and high-performance NRR electrocatalysts in the future.