Recent Advance in Heterogenous Electrocatalysts for Highly Selective Nitrite Reduction to Ammonia Under Ambient Condition

Abstract

Industrial ammonia production mainly relies on the conventional Haber–Bosch process accompanied by high energy consumption and plentiful carbon dioxide emissions, which triggered the recent interest to explore more energy‐efficient and environmentally benign alternatives. Very recently, electrochemical nitrite reduction in an aqueous medium promises new opportunities for advanced, energy‐efficient, and sustainable ammonia production at ambient conditions. The ammonia formation rate and Faradic efficiency are strongly associated with the adopted electrocatalysts; therefore, striving for high‐efficient electrocatalysts is the key to sustainable ammonia production via the electrochemical nitrite reduction reaction. Herein, a critical overview of recent advances in electrochemical nitrite reduction reaction to ammonia is presented, highlighting the latest innovative heterogenous electrocatalysts including noble metal catalysts, transition‐metal‐based catalysts, and their compounds. Meanwhile, the possible reaction pathway of nitrite electroreduction to ammonia, ammonia detection, and catalytic activity descriptor are briefly summarized. Finally, the perspective and research challenges of electrocatalysts that convert nitrite to ammonia are outlined, increasing their contributions in the route of realizing a neutral carbon footprint.

High-Performance Electrocatalytic Reduction of Nitrite to Ammonia under Ambient Conditions on a FeP@TiO2 Nanoribbon Array

“…Precious metal-based catalysts have admirable catalytic activity for the NO 2 – RR. − Their scarcity and high price, nevertheless, pose significant obstacles to their widespread application. It thus holds significant practical importance to explore earth-abundant nonprecious alternatives. − ,− As an transition-metal phosphide, FeP has found applications in electrocatalytic hydrogen evolution and hydrogenation of N 2 and carbon dioxide (CO 2 ), − and it also demonstrates catalytic ability toward the NO 2 – RR . Titanium dioxide (TiO 2 ) featuring abundance, nontoxicity, and excellent chemical stability has gained considerable attention as a support for active nanocatalysts. − Our recent study confirms its NO 2 – RR activity .…”

“…Encouragingly, electrocatalytic N 2 reduction has emerged as a promising approach for green NH 3 production under ambient conditions. − However, the ultralow water solubility and high bond dissociation energy of NN (941 kJ mol –1 ) in N 2 , along with the competitive hydrogen evolution reaction, significantly impact the yield of NH 3 and Faradaic efficiency (FE) for the N 2 reduction reaction. Nitrite (NO 2 – ) is widely present in the environment and highly soluble in water with a lower bond energy (204 kJ mol –1 ) compared to N 2 . − Electrochemical NO 2 – reduction offers an attractive alternative to remove NO 2 – and generate value-added NH 3 simultaneously. The NO 2 – reduction reaction (NO 2 – RR) is a six-electron process and could yield other byproducts like hydrazine (N 2 H 4 ), N 2 , and H 2 , highlighting the importance of developing efficient electrocatalysts with high selectivity for the conversion of NO 2 – to NH 3 .…”

3D cauliflower-like Ni foam: a high-efficiency electrocatalyst for ammonia production via nitrite reduction

“…5 Nitrite (NO 2 À ) demonstrates significantly greater water solubility and relatively lower NQO bond energy (204 kJ mol À1 ), resulting in faster reaction kinetics during the electrolytic reduction of NO 2 À to NH 3 . 6,7 The overuse of agricultural fertilizers, nevertheless, has led to excessive accumulation of NO 2 À in the aquatic ecosystem.…”

“…Great efforts have thus been made to develop non-precious metal-based alternatives. 6,7,[14][15][16][17][18][19][20][21] Ni has emerged as an interesting transition metal toward electrocatalytic NO 2 À RR and several Ni-based such catalysts are available, including vacancy-rich Ni, 22 CuNi alloy, 23 Ni@TiO 2 nanoarray 24 and Ni-carbon nanohybrid, 25,26 etc. Threedimensional (3D) Ni foam constructed by the dynamic hydrogen bubble template (DHBT) method possesses an interconnected open porous structure that can effectively prevent selfagglomeration of Ni during the reaction, eliminating the need for additional carriers and facilitating ion/electron transport for applications.…”

Cobalt-Nanoparticles-Decorated 3D Porous Nitrogen-Doped Carbon Network for Electrocatalytic Nitrite Reduction to Ammonia

“…Ammonia (NH 3 ) is an essential chemical raw material widely applied in the chemical industry, agriculture, pharmaceuticals, etc., and holds great potential as a clean energy carrier with high energy density (4.32 kW h kg –1 ). − Currently, the conventional industrial-scale NH 3 synthesis relies on the energy-intensive Haber–Bosch process, which accounts for approximately 1% of global energy consumption and generates ∼2% of carbon dioxide emissions annually, leading to significant energy and environmental challenges . The electrocatalytic nitrogen (N 2 ) reduction reaction (NRR) has emerged as a promising, pollution-free, and sustainable strategy for NH 3 generation. − Despite its potential, NRR faces challenges like low Faradaic efficiency (FE) and NH 3 yield due to the strong NN bond (941.0 kJ mol –1 ), ultralow water solubility of N 2 , and competition from the hydrogen evolution reaction.…”