Au Sub‐Nanoclusters on TiO₂ toward Highly Efficient and Selective Electrocatalyst for N₂ Conversion to NH₃ at Ambient Conditions

TLDR

N₂ fixation is traditionally energy‑intensive, requiring high pressures and temperatures in the Haber–Bosch process that generates substantial CO₂, while isolated precious‑metal clusters on oxide supports offer well‑defined active sites that can enhance diverse electrochemical reactions. This study demonstrates that Au sub‑nanoclusters (~0.5 nm) on TiO₂ enable electrocatalytic N₂ reduction at ambient conditions. The catalyst consists of 1.542 wt % Au sub‑nanoclusters embedded in TiO₂, providing active sites for N₂ adsorption and reduction. The system achieves a stable NH₃ production rate of 21.4 µg h⁻¹ mg_cat⁻¹ with an 8.11 % Faradaic efficiency at –0.2 V vs RHE, surpassing previous ambient‑condition results and approaching yields obtained under high‑temperature/high‑pressure conditions.

Abstract

As the NN bond in N2 is one of the strongest bonds in chemistry, the fixation of N2 to ammonia is a kinetically complex and energetically challenging reaction and, up to now, its synthesis is still heavily relying on energy and capital intensive Haber-Bosch process (150-350 atm, 350-550 °C), wherein the input of H2 and energy are largely derived from fossil fuels and thus result in large amount of CO2 emission. In this paper, it is demonstrated that by using Au sub-nanoclusters (≈0.5 nm ) embedded on TiO2 (Au loading is 1.542 wt%), the electrocatalytic N2 reduction reaction (NRR) is indeed possible at ambient condition. Unexpectedly, NRR with very high and stable production yield (NH3 : 21.4 µg h-1 mg-1cat. , Faradaic efficiency: 8.11%) and good selectivity is achieved at -0.2 V versus RHE, which is much higher than that of the best results for N2 fixation under ambient conditions, and even comparable to the yield and activation energy under high temperatures and/or pressures. As isolated precious metal active centers dispersed onto oxide supports provide a well-defined system, the special structure of atomic Au cluster would promote other important reactions besides NRR for water splitting, fuel cells, and other electrochemical devices.