Key Takeaways & Executive Findings
- •• • Active-site tuning remains central: noble-metal catalysts require optimized NHx adsorption/dehydrogenation and poisoning suppression; Ni-based catalysts demand regulation of NiOOH-like reconstructed phases to balance activity and selectivity. • • Interfacial engineering controls selectivity and stability: heterointerfaces, defects, and doped coordination environments alter AOR vs. OER competition and product branching toward N2 or oxygenated species. • • Device-oriented development is essential: practical DAFCs, ammonia electrolyzers, and SOFCs are limited by membrane compatibility, mass transport, ammonia crossover, thermal management, and durability, not just intrinsic activity. • • Future progress requires coordinated optimization from active materials to electrode architectures and full-device systems to bridge lab-scale catalysts and industrial ammonia energy technologies.
Abstract
The electrocatalytic ammonia oxidation reaction (AOR) is pivotal for sustainable energy conversion and storage, enabling direct ammonia fuel cells (DAFCs), ammonia electrolysis, and solid oxide fuel cells. This review critically examines recent advances in AOR catalysis, emphasizing active-site regulation, interfacial engineering, and device-oriented catalyst development. For noble-metal catalysts, optimizing adsorption and dehydrogenation of NHx intermediates while mitigating poisoning is essential for sustained activity. Non-noble-metal systems, particularly Ni-based catalysts, require precise control of reconstructed working-state phases such as NiOOH-like species to balance activity and selectivity. Interfacial engineering, including heterointerfaces, defect structures, and doped coordination environments, strongly influences the competition between AOR and oxygen evolution reaction (OER), as well as product branching toward N2 or oxygenated nitrogen species. The review underscores that catalyst optimization now extends beyond bulk composition to the precise regulation of the interfacial reaction microenvironment. Furthermore, practical device operation is governed by membrane/electrolyte compatibility, mass transport, ammonia crossover, thermal management, and long-term durability. Bridging fundamental catalyst studies with deployable ammonia energy technologies requires coordinated optimization from active materials to electrode architectures and full-device systems. This review provides a comprehensive framework for designing next-generation AOR catalysts and accelerating their integration into industrial energy systems.
1. Introduction
Ammonia, as a carbon-free hydrogen carrier, offers a compelling route for decentralized energy storage and transportation. However, its utilization in fuel cells and electrolyzers is bottlenecked by the sluggish kinetics and low selectivity of the electrocatalytic ammonia oxidation reaction (AOR). Conventional noble-metal catalysts, such as platinum, suffer from severe poisoning by nitrogen-containing intermediates, leading to rapid activity decay and insufficient power densities in direct ammonia fuel cells. Non-noble alternatives, particularly nickel-based systems, exhibit promising activity but face challenges in controlling the oxidation state and phase of the active species under operating conditions, often resulting in competing oxygen evolution and mixed product distributions.
This review addresses these bottlenecks by systematically analyzing active-site regulation strategies, including the design of adsorption sites for NHx species and the stabilization of NiOOH-like phases, and by highlighting the critical role of interfacial engineering in steering selectivity. Crucially, it argues that catalyst development must be coupled with device-level considerations—such as membrane compatibility, mass transport, and thermal management—to translate laboratory breakthroughs into practical ammonia-based energy systems. By integrating fundamental insights with engineering constraints, this work provides a roadmap for next-generation AOR catalysts that can meet the demands of industrial deployment.
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ZHANG Xinyuan, YAN Xiao, LIANG Ji (2026). Electrocatalytic Ammonia Oxidation Reaction: From Active Site Regulation to Industrial Device Systems. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4240-7
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Frequently Asked Questions
What are the primary deactivation mechanisms for noble-metal AOR catalysts under continuous operation, and how can they be mitigated?
Noble-metal catalysts, such as Pt, deactivate primarily due to strong adsorption of NHx intermediates and poisoning by nitrogen species, which block active sites. Mitigation strategies include alloying with oxophilic metals to weaken NHx binding and promote dehydrogenation, and introducing surface defects to facilitate desorption. The review emphasizes optimizing adsorption/dehydrogenation behavior while suppressing poisoning to sustain high activity.
How does the reconstruction of Ni-based catalysts into NiOOH-like phases affect AOR selectivity and stability, and what operational parameters are critical?
Ni-based catalysts undergo electrochemical reconstruction to form NiOOH-like species, which are the active phases for AOR. The oxidation state and phase evolution depend on applied potential and electrolyte pH. Precise control of these parameters is necessary to balance catalytic activity and product selectivity, as over-oxidation can lead to OER and reduced N2 selectivity. The review highlights the need to understand active-site evolution under realistic operating conditions.
What are the key interfacial engineering strategies to suppress OER and enhance N2 selectivity in AOR?
Interfacial engineering strategies include constructing heterointerfaces, introducing defect structures, and tuning doped coordination environments. These modifications alter the local adsorption configuration and electronic structure, which can preferentially promote AOR over OER and direct product branching toward N2 rather than oxygenated nitrogen species. The precise regulation of the interfacial reaction microenvironment is now a critical design parameter.
What are the main device-level challenges for integrating AOR catalysts into DAFCs and ammonia electrolyzers, and how do they impact performance?
Device-level challenges include membrane or electrolyte compatibility, mass transport limitations, ammonia crossover, thermal management, and long-term durability. These factors can significantly reduce overall system efficiency and power output, even with highly active catalysts. For example, ammonia crossover through proton-exchange membranes can cause mixed potentials and degrade performance. Therefore, catalyst development must be coupled with electrode architecture and full-device optimization.
What metrics are used to evaluate AOR catalyst performance, and what are the current benchmarks for non-noble metal systems?
Key metrics include onset potential, current density at a given potential, Faradaic efficiency for N2, and stability over time. For non-noble metal systems, particularly Ni-based catalysts, achieving high current densities (e.g., >100 mA/cm²) at low overpotentials (<0.6 V vs. RHE) with >90% N2 selectivity is a target. However, the review notes that direct comparisons are complicated by varying test conditions and the need for standardized protocols.
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