Catalysts for electrochemical ammonia oxidation: Trend, challenge, and promise

Abstract

Developing sustainable and clean energy technology is critial to address the current energy and environmental crisis. As an energy carrier, hydrogen has been getting attention due to its abundance, high energy density, and zero carbon emission. Due to the difficulty of hydrogen storage and transport, the electro-oxidation of ammonia shows great potential for renewable energy since it satisfies both energy supply and environmental protection as a carbon-free fuel with high hydrogen content. However, ammonia electro-oxidation is a sluggish reaction and shows low durability. Understanding the complicated mechanism and intermediates is conducive to developing efficient electrocatalysts with high catalytic activity and durability. This review begins with the ammonia oxidation technologies and their principles. The two typical mechanisms for ammonia electro-oxidation, Oswin-Salomon mechanism and Gerischer-Mauerer mechanism, are discussed, and attention to the poisoning species is included. Then, the electrocatalysts for ammonia reaction are classified into Pt-based catalysts and non-noble metal-based catalysts, and their performances are reviewed with various strategies. Based on the progress on the electrochemical ammonia oxidation catalysts, the challenges and future insight on ammonia oxidation reaction are discussed and proposed.

Coupling electrochemical CO2 reduction with value-added anodic oxidation reactions: progress and challenges

“…According to the dehydrogenation degree of N intermediates in the N-N coupling step, there are two possible pathways for AOR: (1) the adsorbed ammonia undergoes continuous dehydrogenation steps and the N-N coupling step occurs between two *N species; (2) the N-N coupling step occurs between two incomplete dehydrogenated *NH x species followed by further dehydrogenation of *N 2 H y species (x = 1-3 and y = 2-5). [24][25][26] Pt-based catalysts have shown excellent activity in the AOR. The introduction of Ir and Ni into the Pt lattice can decrease the energy barrier of dehydrogenation of *NH 2 to *NH and the ratedetermining step (RDS) on the Pt surface via elevating the dband centre for enhanced *NH adsorption, thereby accelerating the reaction kinetics and reducing the overpotential.…”

In situ decorated Cu2FeSnS4 nanosheet arrays for low voltage hydrogen production through the ammonia oxidation reaction

“…29 Typically, TMSs exhibit higher conductivity, lower band gap, and lower electronegativity compared to their corresponding oxide materials. [30][31][32] Beyond ternary TMSs, quaternary metal sulfides have relatively high structural diversity and energy stability, making them suitable for long-term electrochemical reactions.…”

Highly Selective Ammonia Oxidation on BiVO4 Photoanodes Co‐catalyzed by Trace Amounts of Copper Ions

“…Ammonia (NH 3 ) is an effective liquid hydrogen (H 2 ) carrier due to its high hydrogen content, mild storage conditions and mature infrastructures for handling [1] . Replacing the sluggish (photo)electrocatalytic water oxidation reaction (WOR, 1.23 V RHE ) by the thermodynamically favorable ammonia oxidation reaction (AOR, 0.06 V RHE ) to couple with the cathodic hydrogen evolution reaction (HER) can theoretically save 95 % of energy, which provides an energy‐effective way to achieve a clean energy future [1a,c,2] . Aside from it, highly active and durable AOR (photo)electrocatalysts are also crucial for the low‐temperature direct ammonia fuel cells and the remediation of ammonia‐nitrogen wastewater [3] .…”

“…Aside from it, highly active and durable AOR (photo)electrocatalysts are also crucial for the low‐temperature direct ammonia fuel cells and the remediation of ammonia‐nitrogen wastewater [3] . However, the well‐investigated Pt‐based noble metal catalysts and Ni‐based non‐noble metal electrodes suffer from the rapid inactivation and the inherent high onset potential (≈1.4 V RHE ), respectively [1c,4] . Photoelectrochemical (PEC) ammonia oxidation based on low‐cost and robust semiconductor photoanodes offers a potential to achieve the long‐term stability and the low onset potential for AOR.…”