Developing
cost-efficient electrocatalysts for ambient N2-to-NH3 conversion and revealing the reaction mechanism
are appealing yet challenging tasks. Some transition metal oxides
have been recently used to catalyze the nitrogen reduction reaction
(NRR), but their further applications are greatly impeded because
of their questionable conductivity, poor dispersion, limited active
sites, and so forth. Herein, three-dimensional Ni foam-supported urchin-like
Al-doped Co3O4 nanospheres rich in surface oxygen
vacancies (Al-Co3O4/NF) were prepared via a
hydrothermal process and subsequent annealing treatment. It is shown
that introducing Al atoms into Co3O4 effectively
tunes the electronic properties of the catalyst, and the increased
surface oxygen vacancies induced by Al doping facilitate the activation
of nitrogen. What is more, this urchin-like nanostructure, demonstrating
an ability to limit the coalescence of gas bubbles, enables the rapid
removal of small gas bubbles and better exposure of active sites to
N2, thus yielding an impressive ammonia electrosynthesis
activity (NH3 yield rate: 6.48 × 10–11 mol s–1 cm–2; Faradaic efficiency:
6.25%) in 0.1 M KOH. Electrochemical-based in situ Fourier transform
infrared spectroscopy was employed to study the mechanism of NRR,
indicating an associative alternating pathway.
Recently, ambient electrochemical N2 fixation has gained great attention. However, the commercial Pt‐based electrocatalyst hardly shows its potential in this field. Herein, it is found that the isolated Pt sites anchored on WO3 nanoplates exhibit the optimum electrochemical NH3 yield rate (342.4 µg h−1 mg−1Pt) and Faradaic efficiency (31.1%) in 0.1 m K2SO4 at −0.2 V versus RHE, which are about 11 and 15 times higher than their nanoparticle counterparts, respectively. The mechanistic analysis indicates that N2 conversion to NH3 follows an alternating hydrogenation pathway, and positively charged isolated Pt sites with special Pt−3O structure can favorably chemisorb and activate the N2. Furthermore, the hydrogen evolution reaction can be greatly suppressed on isolated Pt sites decorated WO3 nanoplates, which guarantees the efficient going‐on of nitrogen reduction reaction.
One step towards green ammonia: electrosynthesis of ammonia from nitrogen and thin air over a gold–copper nanoalloy-decorated zeolitic imidazolate framework.
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