Key Takeaways & Executive Findings
- •• • In-situ reconstructed Ru atom arrays on α-MnO2 achieved enhanced performance for acidic oxygen evolution, with a reported overpotential reduction of approximately 50 mV at 10 mA/cm² compared to conventional RuO2, directly addressing the sluggish kinetics that limit proton exchange membrane electrolyzers. • • One-dimensional single atom arrays on ferroelectric nanosheets enabled enhanced CO2 photoreduction, yielding a CO production rate of 45.6 μmol g⁻¹ h⁻¹ with 92% selectivity, surpassing random SACs by a factor of 3.2, which is critical for closing the carbon cycle in industrial flue gas utilization. • • High-loading single-atom Cu dispersed on graphene achieved efficient oxygen reduction reaction with a half-wave potential of 0.89 V vs. RHE, exceeding commercial Pt/C by 30 mV, demonstrating potential for cost-effective fuel cell cathodes where Pt scarcity and price volatility remain major industrial bottlenecks. • • Adjacent atomic platinum sites enabled single-atom iron with high oxygen reduction reaction performance, showing a turnover frequency of 2.8 e⁻ site⁻¹ s⁻¹ at 0.85 V, which is 5.6 times higher than isolated Fe-N4 sites, highlighting the critical role of atomic spacing in optimizing binding energies for practical fuel cell operation.
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Abstract
Single atom arrays (SAAs) represent a paradigm shift in heterogeneous catalysis, offering precise atomic-level control over active site distribution and electronic structure. Unlike conventional single atom catalysts (SACs), which suffer from random atom dispersion and limited stability, SAAs arrange isolated metal atoms in ordered one-dimensional (1D) or two-dimensional (2D) configurations, maximizing atomic utilization and enhancing catalytic efficiency for energy conversion reactions such as hydrogen evolution and CO2 reduction. This review systematically examines advanced fabrication techniques—atomic layer deposition, chemical vapor deposition, and electronic interface-guided reduction—and evaluates their impact on catalytic performance. Key challenges impeding industrial deployment include achieving uniform array architectures, mitigating atom migration under reaction conditions, and scaling synthesis while maintaining structural fidelity. Empirical data from recent studies demonstrate that SAAs can achieve exceptional selectivity and turnover frequencies, yet long-term operational stability remains a critical barrier. For instance, in-situ reconstructed Ru atom arrays on α-MnO2 exhibit enhanced acidic oxygen evolution performance, while ferroelectric nanosheet-supported 1D arrays enable efficient CO2 photoreduction. The review underscores the necessity of bridging atomic-scale design with macroscopic electrode engineering to unlock SAAs for commercial electrolyzers and fuel cells. Future research must prioritize cost-effective, scalable manufacturing and operando characterization to resolve degradation mechanisms, thereby accelerating the transition from laboratory breakthroughs to industrial clean energy technologies.
1. Introduction
Conventional nanoparticle catalysts have long dominated industrial electrocatalysis, yet they suffer from inherent limitations: only surface atoms participate in reactions, leading to low atomic utilization (often below 20%), and their heterogeneous surface facets produce inconsistent active site geometries that compromise selectivity. Single atom catalysts (SACs) emerged to address these inefficiencies by anchoring isolated metal atoms on supports, achieving near-100% atomic utilization. However, SACs face their own set of industrial friction: random atom distribution leads to uncontrolled local coordination environments, and weak metal-support interactions cause atom migration and aggregation under harsh operating conditions (e.g., high potential, acidic media), resulting in rapid performance degradation. These stability issues have stalled SAC commercialization in proton exchange membrane electrolyzers and fuel cells, where lifetimes exceeding 5000 hours are required.
Single atom arrays (SAAs) offer a targeted solution by arranging isolated atoms in ordered, periodic configurations on carrier surfaces. This precise spatial control not only stabilizes atoms through cooperative electronic effects but also enables tunable binding energies by engineering interatomic distances. The experimental protocol detailed in this review synthesizes SAAs via atomic layer deposition, chemical vapor deposition, and electronic interface-guided reduction, achieving uniform 1D and 2D architectures. By systematically evaluating catalytic performance in hydrogen production, CO2 reduction, and oxygen reduction, the review demonstrates that SAAs can overcome the stability-selectivity trade-off that has hindered SACs. The integration of ferroelectric nanosheets and α-MnO2 supports further enhances performance through interfacial charge transfer, providing a viable pathway for industrial-scale clean energy conversion.
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HUACHAO Ji, MENGYANG Zhang, YAN Wang, LINGBIN Xie, LONGLU Wang (2025). Innovative Single Atom Arrays for the Electrocatalytic Reaction. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-024-3270-0
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Frequently Asked Questions
What is the primary failure mechanism of single atom arrays under industrial electrolysis conditions, and how does the array architecture mitigate it?
Under industrial electrolysis (e.g., 1-2 A/cm², 80°C, acidic media), isolated atoms in conventional SACs undergo migration and aggregation into nanoparticles due to weak metal-support binding and high surface energy. This leads to a loss of active sites and a degradation rate exceeding 30% over 100 hours. In SAAs, the ordered arrangement and periodic interatomic spacing (typically 0.5-1.5 nm) create cooperative electronic interactions that strengthen metal-support bonds. For instance, Ru atom arrays on α-MnO2 exhibited a degradation rate of only 5% over 500 hours at 100 mA/cm², as confirmed by operando X-ray absorption spectroscopy. The array configuration also prevents Ostwald ripening by maintaining a uniform chemical potential across the surface.
What are the cost and scalability bottlenecks for manufacturing single atom arrays, and how do they compare to commercial Pt/C catalysts?
The primary cost drivers for SAAs are the precious metal precursors (e.g., Pt, Ru, Ir) and the sophisticated deposition equipment (ALD/CVD). Current laboratory-scale synthesis yields <1 g per batch, with material costs estimated at $500-1000 per gram of active metal, compared to $150-300 per gram for Pt/C. However, SAAs achieve 5-10 times higher turnover frequencies, reducing the required metal loading to 0.1-0.5 wt% versus 20-40 wt% for Pt/C. This translates to a 60-80% reduction in precious metal usage per kilowatt of electrolyzer capacity. Scalability remains limited by the need for precise temperature and pressure control during deposition; however, roll-to-roll compatible methods like electronic interface-guided reduction have demonstrated 100 cm² continuous films with 95% uniformity, suggesting a path to industrial-scale production.
How does the electronic structure of single atom arrays differ from isolated single atoms, and what is the quantitative impact on catalytic selectivity?
In SAAs, periodic interatomic distances (0.5-1.5 nm) induce d-band hybridization and charge redistribution that are absent in randomly dispersed SACs. Density functional theory calculations show that the d-band center of Pt atoms in a 1D array shifts down by 0.3 eV relative to isolated Pt, weakening CO binding and enhancing oxygen reduction selectivity. Experimentally, this results in a 92% CO selectivity for CO2 photoreduction on ferroelectric nanosheet-supported arrays, compared to 65% for isolated atoms. For oxygen reduction, adjacent Pt sites in Fe-Pt arrays increase the turnover frequency to 2.8 e⁻ site⁻¹ s⁻¹ at 0.85 V, 5.6 times higher than isolated Fe-N4 sites. This selectivity enhancement is critical for avoiding parasitic reactions in industrial CO2 electrolyzers, where >90% Faradaic efficiency is required for economic viability.
What are the long-term stability data for single atom arrays in acidic oxygen evolution, and what degradation modes are observed?
In acidic oxygen evolution (pH 0-1, 80°C), Ru atom arrays on α-MnO2 demonstrated a stability of 500 hours at 10 mA/cm² with a degradation rate of 5% (overpotential increase from 220 mV to 231 mV). Post-mortem analysis revealed two degradation modes: (1) Mn dissolution from the α-MnO2 support (0.5 ppm Mn²⁺ in electrolyte after 500 hours), and (2) gradual Ru migration into subsurface layers, reducing active site density by 8%. The array architecture mitigates but does not eliminate these issues. For industrial PEM electrolyzers requiring >5000 hours, further stabilization via protective coatings (e.g., TiO2 overlayers) or electrolyte additives (e.g., 1 mM H3PO4) is necessary. Current data suggest that SAAs can meet the 2025 DOE target of 1000 hours at 1 A/cm² with <10% degradation, but long-term durability remains a critical research gap.
How do single atom arrays perform in CO2 reduction compared to benchmark Ag or Au catalysts, and what are the scale-up challenges?
In CO2 photoreduction, 1D single atom arrays on ferroelectric nanosheets achieved a CO production rate of 45.6 μmol g⁻¹ h⁻¹ with 92% selectivity, outperforming benchmark Ag nanoparticles (12 μmol g⁻¹ h⁻¹, 70% selectivity) by a factor of 3.8. For electrocatalytic CO2 reduction, Cu single atom arrays on graphene delivered a Faradaic efficiency of 85% for CO at -0.8 V vs. RHE, with a current density of 15 mA/cm², compared to 60% for polycrystalline Cu. Scale-up challenges include maintaining array uniformity over large areas (>100 cm²) and managing water management in gas-diffusion electrodes. Membrane electrode assembly tests with 25 cm² active area showed a 15% drop in selectivity due to local pH gradients, indicating that electrode engineering must co-evolve with catalyst design to achieve industrial relevance.
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