The Breakthrough in Single-Atom Catalyst Design at Nagoya University

Nagoya University researchers have made a groundbreaking advancement in the field of electrocatalysis by establishing new design principles for single-atom catalysts (SACs). Led by Distinguished Professor Yusuke Yamauchi from the Graduate School of Engineering, the team achieved near-100% utilization of active sites in SACs, addressing a long-standing challenge in materials science. This innovation promises to revolutionize energy conversion technologies, particularly in fuel cells and electrolyzers, by maximizing the efficiency of non-precious metal catalysts.

The study, published in Nature Communications, demonstrates how a novel surfactant-assisted freeze-casting (SAFC) method transforms metal-organic frameworks (MOFs) into two-dimensional (2D) nanocarbon structures. These structures expose nearly all single metal atoms for catalytic reactions, rivaling or surpassing expensive platinum-based catalysts in oxygen reduction reaction (ORR) performance.

Understanding Single-Atom Catalysts and Their Promise

Single-atom catalysts represent the pinnacle of atomic efficiency in heterogeneous catalysis. Unlike traditional nanoparticle catalysts, SACs disperse individual metal atoms on a support material, achieving 100% theoretical atom utilization. This makes them ideal for applications requiring high selectivity and activity, such as the oxygen reduction reaction in proton exchange membrane fuel cells (PEMFCs).

In PEMFCs, ORR at the cathode is the rate-limiting step, traditionally relying on scarce platinum (Pt). SACs, particularly those based on iron-nitrogen-carbon (Fe-N-C), offer a cost-effective alternative. However, real-world performance has lagged due to incomplete site utilization, where many atoms remain inaccessible buried within porous supports.

Overcoming Key Challenges in SAC Utilization

Conventional SACs synthesized from MOFs or zeolitic imidazolate frameworks (ZIFs) suffer from disordered three-dimensional (3D) stacking and dense micropores. This buries up to 80% of active sites, hindering mass transport (MT) of reactants like O₂ and OH^- and electron transport (ET). Studies show typical site utilization (U_site) below 20-30%, far from theoretical maxima.

Nagoya's team quantified this using scanning electrochemical microscopy (SECM) and nitrite stripping voltammetry, revealing U_site as low as 25% in standard 3D FeNC catalysts. Their solution: engineer macro- and micro-scale structures for optimal accessibility.

The SAFC Methodology: A Step-by-Step Innovation

The SAFC process begins with synthesizing ~50 nm Fe-doped ZIF-8 nanoparticles. These are surface-modified with sodium dodecyl sulfate (SDS) surfactant at an optimal 1.62 mM concentration, enabling electrostatic repulsion for uniform dispersion.

• Dispersion in water and rapid freezing in liquid nitrogen forms ice crystals directing nanoparticles into single-layer 2D superstructures.
• Freeze-drying preserves the ordered alignment.
• Pyrolysis at 1100°C under N₂ applies dual stress—from SDS shells and tight particle packing—yielding concave, mesopore-rich (80.3% mesopores) 2D FeNC with surface area 1637 m²/g.

This results in Fe single atoms (1.01 wt%) uniformly anchored in pyridinic N-coordinated sites, confirmed by HAADF-STEM, EXAFS, and XPS.

Outstanding Electrochemical Performance

In 0.1 M KOH, 2D FeNC exhibits a half-wave potential (E_1/2) of 0.958 V vs. RHE, surpassing commercial Pt/C (0.906 V) and 3D FeNC (0.914 V). Kinetic current at 0.93 V reaches 66.2 mA/cm², with Tafel slope 45.6 mV/dec indicating favorable kinetics.

Site density (SD_mass) hits 6.52 × 10¹⁹ sites/g, yielding U_site of 99.4%. Turnover frequency (TOF) is 113.8 e^- site^-1 s^-1. Durability shines with only 4 mV E_1/2 shift after 30,000 cycles.

Photo by Nemanja Milenkovic on Unsplash

Operando techniques like EIS and in situ ATR-FTIR confirm enhanced MT/ET and associative ORR pathway via weaker *OOH binding.

Practical Applications in Flexible Zinc-Air Batteries

2D FeNC paired with RuO₂ in flexible Zn-air batteries (ZABs) delivers peak power density 48.4 mW/cm² and current density 93.5 mA/cm² at 1.0 V—over twice Pt/C benchmarks. Devices power smartphones and timers, showcasing real-world viability.

This aligns with Japan's push for clean energy, where fuel cell vehicles (FCVs) like Toyota Mirai rely on Pt catalysts costing thousands per kW.

Universality: Extending to Multiple Metals and Reactions

SAFC proves versatile across transition metals (Co, Ni, Mn, Cu) and noble metals (Ir, Pt). 2D MNCs outperform 3D counterparts in ORR. Notably, 2D IrNC excels in formic acid oxidation (peak current 1.4 mA/cm²), and 2D PtNC in methanol oxidation.

• CoNC: E_1/2 0.89 V
• NiNC: Enhanced selectivity
• PtNC: 2x higher activity than commercial Pt

This broadens SAC applications to electrolyzers, CO₂ reduction, and beyond.

Nagoya University's Leadership in Materials Engineering

Nagoya University, ranked 6th in Japan (THE World Rankings 2026) and top in engineering, fosters interdisciplinary innovation. Its Graduate School of Engineering excels in nanotechnology and energy materials, producing six Nobel laureates since 2001.

Prof. Yamauchi, dual-affiliated with University of Queensland, brings global expertise. His lab's focus on mesoporous nanomaterials has yielded over 500 papers, advancing SACs from theory to practice.

Implications for Japan's Higher Education and Energy Sector

This research bolsters Japan's hydrogen society goals under the Basic Hydrogen Strategy, targeting 20% FCV adoption by 2030. SACs could slash Pt use by 90%, cutting PEMFC costs from $100/kW to under $30/kW.

In higher education, it highlights collaborative training: international co-authors from China, Australia, Japan underscore Nagoya's global networks. For Japanese universities, it exemplifies translational research, attracting MEXT funding and industry partnerships like Toyota.

The global SAC market, valued at $138M in 2025, is projected to reach $670M by 2035 (CAGR 17%). Japan's leadership positions its academics for patents and startups.

Future Outlook and Remaining Challenges

While SAFC unlocks SAC potential, scalability, acidic stability (tested preliminarily), and in-situ dynamics remain hurdles. Yamauchi envisions: "...atomic-level functionality drawn out across the entire material."

Next steps: Pilot-scale synthesis, integration into PEMFCs, and AI-accelerated design. For Japan, this could accelerate net-zero by 2050.

Photo by Andy Kuo on Unsplash

Stakeholder Perspectives and Expert Opinions

Industry experts praise the work: "A game-changer for non-Pt ORR catalysts," per a fuel cell analyst. Academics note its synergy with Japan's Supercomputer Fugaku for simulations.

Students and postdocs at Nagoya benefit from Yamauchi's mentorship, with opportunities in AIBN collaborations.