Greatly Improving Electrochemical N₂ Reduction over TiO₂ Nanoparticles by Iron Doping

Abstract

Titanium‐based catalysts are needed to achieve electrocatalytic N2 reduction to NH3 with a large NH3 yield and a high Faradaic efficiency (FE). One of the cheapest and most abundant metals on earth, iron, is an effective dopant for greatly improving the nitrogen reduction reaction (NRR) performance of TiO2 nanoparticles in ambient N2‐to‐NH3 conversion. In 0.5 m LiClO4, Fe‐doped TiO2 catalyst attains a high FE of 25.6 % and a large NH3 yield of 25.47 μg h−1 mgcat−1 at −0.40 V versus a reversible hydrogen electrode. This performance compares favorably to those of all previously reported titanium‐ and iron‐based NRR electrocatalysts in aqueous media. The catalytic mechanism is further probed with theoretical calculations.

Vacancy Engineering of Iron‐Doped W18O49 Nanoreactors for Low‐Barrier Electrochemical Nitrogen Reduction

“…The deconvoluted high‐resolution W 4f spectra of pristine and W 18 O 49 ‐16Fe nanowires suggests both W 5+ and W 6+ species present in the samples (Figure d, Figure S7 b), which is consistent with the distorted edge‐sharing crystal structure of W 18 O 49 forming low‐valence W elements and metallic W–W interaction in the lattice . Compared with the pristine W 18 O 49 , the W 18 O 49 ‐16Fe showed an increased W 5+ /W 6+ ratio from 1.2 to 1.7 and a clear shift to the lower binding energy (Table S3), indicating the partial reduction of W 6+ into W 5+ associated with the increase of O vac . On the other hand, for the Fe 2p spectra, it can be deconvoluted into four peaks at 710.5, 712.3, 723.8 and 725.6 eV (Figure e, Figure S7), corresponding to the Fe 2+ 2p 3/2 , Fe 3+ 2p 3/2 , Fe 2+ 2p 1/2 , and Fe 3+ 2p 1/2 states, respectively .…”

“…Compared with the pristine W 18 O 49 , the W 18 O 49 ‐16Fe showed an increased W 5+ /W 6+ ratio from 1.2 to 1.7 and a clear shift to the lower binding energy (Table S3), indicating the partial reduction of W 6+ into W 5+ associated with the increase of O vac . On the other hand, for the Fe 2p spectra, it can be deconvoluted into four peaks at 710.5, 712.3, 723.8 and 725.6 eV (Figure e, Figure S7), corresponding to the Fe 2+ 2p 3/2 , Fe 3+ 2p 3/2 , Fe 2+ 2p 1/2 , and Fe 3+ 2p 1/2 states, respectively . Besides, the additional pre‐peak in the low‐binding‐energy region (708.7 eV) accounts for the Fe ions with a lower oxidation state than Fe 2+ , further revealing the existence of O vac in the neighboring sites of Fe dopants …”

Low‐Coordinate Step Atoms via Plasma‐Assisted Calcinations to Enhance Electrochemical Reduction of Nitrogen to Ammonia

“…To verify the N source of the obtained NH 3 , 15 N isotopic labeling experiments combined with 1 H nuclear magnetic resonance (NMR) technique were further carried out. [ 6,9,18 ] When 15 N 2 is chosen as the feeding gas, 1 H NMR spectrum for the electrolyte after the electrocatalytic process at −0.2 V versus RHE shows two resonance peaks, which nicely match the standard 15 NH 4 + with a doublet coupling (Figure S11, Supporting Information). This result further confirms that the synthesized NH 3 is derived from the N 2 electroreduction over IrP 2 @PNPC‐NF.…”

“…To address this critical but thorny problem, stepped facets and doping modification may be the two effective ways to intrinsically enhance their catalytic activity. [ 16–21 ] On the one hand, stepped facets usually have low coordination number (CN) of surface atoms, where these unsaturated sites can more favorably adsorb and activate N 2 molecule compared with the flat facets. [ 22 ] For example, Zhang's group reported tetrahexahedral gold nanorods enclosed by stepped {730} facets that exhibit unexpectedly electrocatalytic NRR performance, indicating low‐coordinate step atoms are the favorable active sites in optimizing the activity of the metal‐based catalysts.…”

Electrochemical Synthesis of Ammonia Based on a Perovskite LaCrO3 Catalyst

“…The overall reaction with the release of a second NH 3 molecule is exothermic at both facets and the calculations show that both reaction pathways are viable. [26][27][28][29][30] Lanthanum Chromite (LaCrO 3 ) nanoparticles were synthesized and evaluated as the NRR electrocatalyst in an aqueous based cell under ambient conditions. The particles had a homogenous size distribution and planes were (110) oriented and the transition metal Cr contained a mixed oxidation states of 3 + and 6 + at the catalyst surface.…”