Highly Efficient Electrochemical Nitrate Reduction to Ammonia in Strong Acid Conditions with Fe₂M‐Trinuclear‐Cluster Metal–Organic Frameworks

Abstract

Nitrate-containing industrial wastewater poses a serious threat to the global food security and public health safety. As compared to the traditional microbial denitrification, electrocatalytic nitrate reduction shows better sustainability with ultrahigh energy efficiency and the production of high-value ammonia (NH 3 ). However, nitratecontaining wastewater from most industrial processes, such as mining, metallurgy, and petrochemical engineering, is generally acidic, which contradicts the typical neutral/alkaline working conditions for both denitrifying bacteria and the state-of-the-art inorganic electrocatalysts, leading to the demand for pre-neutralization and the problematic hydrogen evaluation reaction (HER) competition and catalyst dissolution. Here, we report a series of Fe 2 M (M = Fe, Co, Ni, Zn) trinuclear cluster metal-organic frameworks (MOFs) that enable the highly efficient electrocatalytic nitrate reduction to ammonium under strong acidic conditions with excellent stability. In pH = 1 electrolyte, the Fe 2 Co-MOF demonstrates the NH 3 yield rate of 20653.5 μg h À 1 mg À 1 site with 90.55 % NH 3 -Faradaic efficiency (FE), 98.5 % NH 3 -selectivity and up to 75 hr of electrocatalytic stability. Additionally, successful nitrate reduction in high-acidic conditions directly produce the ammonium sulfate as nitrogen fertilizer, avoiding the subsequent aqueous ammonia extraction and preventing the ammonia spillage loss. This series of cluster-based MOF structures provide new insights into the design principles of high-performance nitrate reduction catalysts under environmentally-relevant wastewater conditions.

Modulation of Reactive Hydrogen Adsorbed on Dual-Active Site NiMoO4 Nanocubes for Reduction of Nitrate to Ammonia

“…Isotopic labeling combined with NMR measurements is a powerful method for detecting N sources in NH 3 . 46,47 Therefore, 14 Nand 15 N-labeled NO 3 − were used as the nitrogen source for the NO 3 − RR test and the product was detected by 1 H NMR spectroscopy. In Figure 3f, only a typical double peak of 15 NH 4 + was collected when 15 NO 3 − was added.…”

“…Undoubtedly, a proper catalyst design is essential for the high efficiency and selectivity of the electrocatalytic NO 3 − RR to NH 3 . Nonprecious monometallic catalysts, such as iron, 13,14 cobalt, 15,16 and copper, 17−20 are the main choices for NO 3 − RR owing to their high cost-effectiveness, but their catalytic activity and selectivity are inadequate to meet the growing demand of NH 3 synthesis. Furthermore, other materials, nickel, have rarely been investigated because they are generally considered unsuitable for NO 3 − RR as the HER is their main competing reaction.…”

Vapor‐Phase Synthesis of Electrocatalytic Covalent Organic Frameworks

“…The developed process allows the bottom-up synthesis of COFs that carry pyrrole-N 4 motifs, well known for their electrocatalytic properties. [20] We show that by changing the metal center, we can tune the selectivity and activity of our electrocatalysts for electrochemical nitrate reduction reaction (eNRR) and oxygen reduction and evolution reactions (ORR/OER) in an aprotic medium, rivaling [21] the reported performance of catalysts used for these reactions [22][23][24][25][26] In the first step, a pulse of TAPP (monomer) was given. Thereafter, the reactor was pumped down and purged to reach the base pressure.…”

“…This areal yield, with loading of 100 μg cm −2 , translates to a per-mass yield of 60 mg h −1 mg −1 , threefold higher than previously reported values. [35][36][37][38][39][40][41] Compared with similar COFs prepared by a solution phase technique, [21] our CuPOR-COF catalyst's performance presents a 20-fold higher yield. The F.E.% declines at higher potentials due to the competing hydrogen evolution on the electrodes (Figure 3B).…”

Vanadium-Doped Bimetallic Nanoporous Metal–Organic Frameworks as Bifunctional Electrocatalysts for Urea-Assisted Hydrogen Production

“…31−33 Lv et al report a series of Fe 2 M (M = Fe, Co, Ni, Zn) trinuclear cluster constructed metal−organic frameworks (MOFs) that enable highly efficient electrocatalytic nitrate reduction to ammonium with excellent stability. 31 Gu et al synthesized Fe 2 Co-MOF and Fe 2 Zn-MOF catalysts with extremely low overpotential of 339 mV@10 mA cm −2 for OER and 221 mV@10 mA cm −2 for HER, respectively. 34 These works indicate that the element doping strategy is very effective to enhance the electrocatalytic performance of target trinuclear metal−organic frameworks.…”