Sustainable Nitrogen Fixation to Produce Ammonia by Electroreduction of Plasma-Generated Nitrite

Abstract

One-step electrocatalytic N 2 fixation is of emerging interest but is retarded due to the tough dissociation of the N 2 triple bond and low NH 3 selectivity. Here, a plasma-electrocatalytic integrated strategy is reported to be effective to circumvent this dilemma and realize high-performance N 2 fixation via decoupling the reaction to two steps with NO x − serving as an intermediary: (i) non-thermal plasma (NTP) drives air activation into highly active NO x − intermediates, and (ii) subsequent electroreduction of the resultant NO x − into NH 3 . A gliding arc−microwave conjunction plasma mode was found to be preferred to achieve an optimal NO 2 − -N concentration of 2844.31 μg mL −1 , adopting 0.5 M KOH as the absorption solution in the first step. For the next ENO 2 − RR step, plasma-treated 0.5 M KOH was directly used as electrolyte, with well-designed Cu 2 Pd nanodots anchored on carbonized bacterial cellulose (Cu 2 Pd/CBC) as electrocatalyst. An exceptional ENO 2 − RR performance, including a superior R NHd 3 of 1956.65 μg h −1 mg −1 , highest FE of 93.79%, and long time stability of 30 h, was attained for Cu 2 Pd/CBC, outperforming the counterparts Cu/CBC and Pd/CBC. The synergism of CuPd bifunctional catalytic sites is the key to the greatly enhanced electrocatalytic activity via improving the adsorption of NO 2 − and the related intermediates while simultaneously supplying sufficient protons. This work provides an alternative strategy toward sustainable and distributed on-site ammonia synthesis.

Sustainable ammonia synthesis from air by the integration of plasma and electrocatalysis techniques

“…As depicted, plasma excitation is divided into two stages: gliding arc plasma ignition by a high-frequency high-voltage power supply in the discharge tube and the strengthening of the plasma torch by microwave power when it approaches the microwave reactor. The plasma-generated NO x streaming from the outlet was absorbed by the KOH solution to form NO x − (NO 2 − and NO 3 − ) in this work based on the following equations: 48,49 NO + NO 2 + 2OH − → 2NO 2 − + H 2 O2NO 2 + 2OH − → NO 2 − + NO 3 − + H 2 O…”

Insights on the Mechanism of Surface-Catalyzed Oxidative Nitrogen Fixation Based on Liquid-Phase Bubble Pin-Plate Discharge

“…Vibrational excitation of N 2 and O 2 molecules provides the energy required to overcome the activation barrier for the nonthermal Zeldovich mechanism. 20,21,24,30,31 It involves two crucial steps: the reaction of excited-state N 2 (v) molecules and O• radicals (R1) and the reaction of excited-state O 2 (v) molecules to N• radicals (R2) (where v represents vibrationally excited states). 32−34 Furthermore, the participation of water vapor can further extend the Zeldovich mechanism: the N• radical forms NO (R3) by reacting with the OH produced by hydrolysis.…”

A High-Throughput Screening toward Efficient Nitrogen Fixation: Transition Metal Single-Atom Catalysts Anchored on an Emerging π–π Conjugated Graphitic Carbon Nitride (g-C10N3) Substrate with Dirac Dispersion

“…10 This process has a large carbon footprint, accounting for 1−2% of the global total energy consumption 11 and meanwhile discharging a large amount of greenhouse gas annually. 12 Considering such unwilling costs in energy and environment, it is highly desirable to find a cost-effective and sustainable technology to achieve highly efficient synthesis for N 2 reduction. Under such circumstances, the electrocatalytic nitrogen reduction reaction (NRR) that directly produces NH 3 from N 2 and H 2 O at mild conditions stands as an almost perfect NH 3 production process because it is a sustainable, environmentally benign, and clean approach that has aroused worldwide scholarly interest in the past few years.…”

“…Currently, industrial-scale NH 3 synthesis has mainly been achieved through the capital- and energy-intensive Haber-Bosch (H–B) approach usually necessitating severe temperature (300–600 °C) and ultrahigh pressure (150–300 atm), which is unsustainable and disadvantageous . This process has a large carbon footprint, accounting for 1–2% of the global total energy consumption and meanwhile discharging a large amount of greenhouse gas annually . Considering such unwilling costs in energy and environment, it is highly desirable to find a cost-effective and sustainable technology to achieve highly efficient NH 3 synthesis for N 2 reduction.…”