Scientists have developed a new catalyst that uses both single atoms and engineered defects to improve the sluggish oxygen evolution reaction (OER), a key step in green hydrogen production.
Study: Dual-Site Synergistic Mechanism via Single-Atom and Vacancy Drives Lattice Oxygen Activation in Layered Double Hydroxides. Image Credit: Forance/Shutterstock.com
The study, published in Advanced Science, demonstrates how ion irradiation can precisely create oxygen vacancies in nickel-iron layered double hydroxides (NiFe-LDH) while anchoring molybdenum (Mo) single atoms, resulting in a highly active and exceptionally stable electrocatalyst.
OER remains a major bottleneck in water splitting because its reaction steps are slow and energetically demanding. NiFe-LDH materials are among the most promising low-cost catalysts, yet many of their oxygen atoms remain inactive, limiting overall efficiency.
While researchers have tried doping, heterostructures, and defect engineering, the interaction between defects and metal centres has remained poorly understood.
This study directly addresses that gap by creating a catalyst where oxygen vacancies and Mo single atoms interact in a controlled way, promoting lattice oxygen activation – a mechanism increasingly recognised as central to high OER performance.
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Controlled Defects Through Ion Irradiation
The team grew NiFe-LDH nanosheets on titanium foil via hydrothermal synthesis, then exposed them to argon ions at carefully chosen fluences (1014–1015 ions cm-2).
The irradiation introduced oxygen vacancies without disrupting the nanosheet structure. These vacancies later served as anchoring points for Mo single atoms added in a second hydrothermal step.
Advanced imaging techniques, including HAADF-STEM, XPS, XANES, EXAFS, and EPR, showed that Mo atoms were uniformly dispersed, stabilised by nearby vacancies, and that the LDH lattice retained its structural integrity.
Raman spectroscopy confirmed both vacancy formation and Mo-O coordination.
High Activity and Industrial-Level Stability
The dual-site catalyst (SAMo-NiFe LDH/Ti) showed a dramatic improvement in oxygen evolution performance. The overpotential fell from 458 mV in pristine NiFe-LDH to 232 mV at 10 mA cm-2 – surpassing commercial RuO2.
Reaction kinetics also improved, with a Tafel slope of 51.9 mV dec-1 and significantly reduced charge-transfer resistance.
Crucially, the catalyst maintained stable operation for more than 600 hours at an industrial-scale current density of 500 mA cm-2. Post-analysis revealed negligible Mo loss, demonstrating that the vacancies effectively confine single atoms and suppress their migration.
Direct Evidence for Lattice Oxygen Participation
Using 18O isotope-labelling and differential electrochemical mass spectrometry, the researchers detected clear 34O2 and 36O2 signals, direct proof that lattice oxygen participates in OER on this catalyst.
The catalyst also showed strong pH dependence and was inhibited by tetraalkylammonium ions, further confirming the lattice-oxygen mechanism (LOM).
The paper distinguishes two types of vacancies: those adjacent to Mo atoms, which directly participate in the reaction, and more distant vacancies, which subtly tune the local environment. Both contribute to the improved performance.
Density functional theory calculations showed that inserting Mo at Ni sites weakens Mo-O bonds, increasing oxygen mobility. Meanwhile, oxygen vacancies increase antibonding electron occupancy and weaken Ni-O bonds.
Together, these effects lower the energy barrier for oxygen intermediates and reduce the overall OER overpotential from 2.34 eV (pristine) to 1.80 eV in the Mo-and-vacancy configuration.
This dual-site interaction emerges as a powerful lever for activating lattice oxygen, addressing the limitations of conventional adsorbate-based mechanisms.
Framework for Future Catalyst Design
With a high Mo single-atom loading of 7.4 wt.% and strong long-term stability, the study highlights ion-irradiation as a precise and controllable approach to defect engineering, without implying immediate industrial scalability.
The authors note that extending this strategy to other transition-metal systems could help establish broader design rules for coupling single atoms with defects.
By integrating experimental measurements with theoretical modelling, the work provides a blueprint for designing future catalysts that harness lattice oxygen mechanisms and deliver high efficiency with long-term performance.
Journal Reference
Wu, S. et al. (2025). Dual-Site Synergistic Mechanism via Single-Atom and Vacancy Drives Lattice Oxygen Activation in Layered Double Hydroxides. Advanced Science, e15407. DOI: 10.1002/ADVS.202515407
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