Ag@TiO₂ as an Efficient Electrocatalyst for N₂ Fixation to NH₃ under Ambient Conditions

Abstract

With the use of traditional Haber-Bosch N 2 fixation, a huge amount of CO 2 emission bring a huge burden to the environment. Electrochemical N 2 reduction provides an environmentalfriendly and sustainable alternative to NH 3 synthesis at ambient conditions. Herein, we report our recent experimental finding that Ag composited with TiO 2 can greatly improve the N 2 reduction reaction performance of TiO 2 toward ambient conversion. In 0.1 M Na 2 SO 4 (pH = 7), such electrocatalyst achieves a large NH 3 yield rate of 14.88 μg h À 1 mg À 1 cat. with a Faradaic efficiency of 6.2 % at À 0.70 V vs. reversible hydrogen electrode. Besides, it also demonstrates high electrochemical and structural stability for NH 3 generation. NH 3 is a basic raw material for manufacturing synthetic chemicals, such as fertilizers, dyes, medicaments and explosives, etc. [1][2][3][4][5] Currently, large-scale NH 3 production is still dominated by the Haber-Bosch process with intensive energy input and large amount of CO 2 emission under harsh conditions. [6] Therefore, it is urgent to develop a sustainable and efficient synthetic method for NH 3 production to meet the increasing world demands.Electrochemical N 2 reduction has aroused great attention as an attractive environmental-friendly alternative for artificial N 2to-NH 3 fixation. [7][8][9][10] Nevertheless, this process needs advanced electrocatalysts for the N 2 reduction reaction (NRR) to effectively break the high bond energy of N 2 (940.95 kJ mol À 1 ) and activate dinitrogen for alleviating energy barriers. [11,12] Consequently, considerable attention has recently been paid to the exploration of efficient NRR catalysts. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] Among them, TiO 2 is an appealing catalytic material for its chemical and thermal stability, good biocompatibility, and environmentally benigh nature. [33][34][35] Our previous study suggests that TiO 2 nanosheet is active for NRR. [34] Heteroatoms (Cu, [17] B, [36] V, [37] Zr, [38] Fe, [39] La [40] and Mn [41] ) doping and graphene hybridization [42] are also effective strategies to enhance the NRR performance of TiO 2 . Meantime, hybridization with noble metals (Au, Pt, Ru) also leads to improve NRR performance of TiO 2 . [43][44][45] Compared with above noble metals, Ag is more earth-abundant and thus holds promise for more widespread use. It is established that Ag can improve the electron transfer rate of Ag/TiO 2 hybrid, [46,47] which is beneficial to its applications in photocatalysis (dye degradation, [48,49] H 2 evolution, [50,51] ) and supercapacitor. [52] However, the use of such hybrid in NRR has not been investigated before.In this work, we report on the development of Ag@TiO 2 for N 2 reduction electrocatalysis. When tested in N 2 -saturated 0.1 M Na 2 SO 4 , this catalyst achieves a large NH 3 yield rate of 14.88 μg h À 1 mg À 1 cat. with a FE of 6.2 % at À 0.70 V vs. reversible hydrogen electrode (RHE). Meanwhile, outstanding durability and reproducibility are also obtain...