Interfacial Engineering Promoting Electrosynthesis of Ammonia over Mo/Phosphotungstic Acid with High Performance

Abstract

Electrochemical nitrogen reduction reaction (eNRR) is recognized as a promising approach for ammonia synthesis, which is, however, impeded by the inert nitrogen and the unavoidable competing hydrogen evolution reaction (HER). Here, a Mo-PTA@CNT electrocatalyst in which Mo species are anchored on the fourfold hollow sites of phosphotungstic acid (PTA) and closely embedded in multi-walled carbon nanotubes (CNT) for immobilization is designed and synthesized. Interestingly, the catalyst presents a high ammonia yield rate of 51 ± 1 µg h −1 mg cat.−1 and an excellent Faradaic efficiency of 83 ± 1% at −0.1 V versus RHE under ambient conditions. The concentrations of NH 4 + are also quantitatively calculated by 1 H NMR spectra and ion chromatography. Isotopic labeling identifies that the N atom of the formed NH 3 originates from N 2 . The controlled experiments confirm a strong interaction between Mo-PTA and N 2 with an adsorption energy of 50.46 kJ mol −1 and activation energy of 21.36 kJ mol −1 . More importantly, due to CNT's gas storage and hydrophobicity properties, there is a fourfold increase in N 2 content. The concentration of H 2 O is reduced by more than half at the interface of the electrode. Thus, the activity of eNRR can be significantly improved with ultrahigh electron selectivity.

Recent advances in material design and reactor engineering for electrocatalytic ambient nitrogen fixation

“…To assess the distribution of N 2 and H 2 O molecules at the electrode interface, Liao et al performed MD simulations of phosphotungstic acid (PTA)@carbon nanotubes. 240 At the catalyst and electrolyte interface, Mo-PTA has a nitrogen distribution density of around 0.19 nm À3 , while pure CNT has a nitrogen distribution density of 0.50 nm À3 . This suggests that carbon nanotubes will aid in nitrogen enrichment at the interface.…”

Facile Synthesis and High‐Value Utilization of Ammonia

“…Recently, our group anchored PTA‐based catalysts in carbon nanotubes (CNT) with hydrophobicity and nitrogen enrichment ability via a simple immersion method to regulate electrode structure. [ 35 ] The introduction of CNT contributes to the reconstruction of the gas‐liquid‐ solid reaction interface, in which the distribution content of H 2 O molecules at the interface reduces and storage space is built for N 2 molecules (Figure 9). As a result, N 2 molecules could accumulate…”

“…Illustrations of the initial and final simulated structures: (c) Mo‐PTA‐liquid; (d) CNT‐liquid; (e) Mo‐PTA@CNT‐liquid. [ 35 ]…”

Holey reduced graphene oxide-assisted oxide-derived Bi for efficient nitrogen electroreduction

“…10 However, this eld has been overshadowed by two major challenges which result in an excessively low NRR performance: (1) the inert N 2 is difficult to activate under ambient conditions because of its strong triple bonds; (2) the undesired hydrogen evolution reaction (HER) occurs simultaneously during the NRR. 11,12 To surmount these issues, numerous advanced electrocatalysts have been developed adhering to the principle of activating N 2 and/or restraining the HER. [13][14][15][16] Frustratingly, most of them failed to achieve high expectations and suffered from limited NH 3 yields and low Faraday efficiency.…”