Oxygen vacancies are missing oxygen atoms in an oxide lattice, and they are routinely introduced to tune the electronic structure of catalysts for fuel cells, metal–air batteries and green chemical synthesis. Conventionally, scientists count vacancies and assume more is better, or at least that all vacancies behave alike. The new work challenges that assumption at a fundamental level. When an oxygen atom leaves the lattice, it can leave behind electrons that either remain trapped at the vacancy site or are transferred to neighbouring metal cations. These two configurations correspond to distinct colour centres, known as F centres: an electropositive F1 centre, in which the electrons are not localized at the vacancy, and an electroneutral F2 centre, in which two electrons are trapped within the vacancy itself.

The challenge for the team, led by Xiaoyuan Zhang, Jingwen Sun and Junwu Zhu of Nanjing University of Science and Technology, was to isolate the effect of charge state from every other variable. To do this, they devised a template-assisted synthesis in which the atmosphere during preparation was carefully regulated, allowing them to produce zirconia samples, ZrO2−x, that contain predominantly F1 or predominantly F2 centres while keeping the crystal structure, particle morphology and vacancy concentration essentially unchanged. This clean experimental design meant that any difference in catalytic behaviour could be attributed directly to the charge state of the defects rather than to confounding structural differences.

Characterization confirmed the distinction. Electron paramagnetic resonance spectroscopy, which is sensitive to unpaired electrons, revealed the paramagnetic signature of the F1-type vacancies, while complementary measurements of the electronic structure showed the different local environments around zirconium cations adjacent to each vacancy type—F1-Zr4+ versus F2-Zr3+ configurations. X-ray absorption, electron energy-loss spectroscopy and photoluminescence measurements all supported the picture of two electronically distinct but structurally equivalent defect species. Crucially, electrochemical scanning transmission electron microscopy showed that the catalysts remained stable under operating conditions, ruling out structural reconstruction as the source of the differing reactivity.

The electrochemical consequences were striking. When the electroneutral F2 centres dominated, the catalyst favoured the two-electron oxygen reduction pathway, selectively converting oxygen into hydrogen peroxide. When the electropositive F1 centres dominated, the reaction instead proceeded toward full four-electron reduction, cleaving the oxygen–oxygen bond and producing water. Hydrogen peroxide electrosynthesis is a rapidly growing field because the compound is a green oxidant used in water treatment, disinfection and chemical manufacturing, and producing it on-site in an electrochemical cell could replace the energy-intensive anthraquinone process. A catalyst whose selectivity can be switched by defect charge state therefore has immediate practical appeal.

To understand the mechanism, the researchers deployed in situ electrochemical electron paramagnetic resonance, tracking the paramagnetism of the F centres while the reaction ran, together with in situ Raman spectroscopy to follow the evolution of reaction intermediates. The results overturned a common intuition. The electroneutral F2 centre, despite being the site where electrons are trapped, is not the primary adsorption site for oxygen. Instead, it acts through dynamic electronic compensation: it continuously donates and withdraws electron density to and from adjacent zirconium sites, stabilizing the adsorbed *OOH intermediate that is the hallmark of the two-electron pathway. It is this dynamism, rather than direct binding, that makes F2 centres the gatekeepers of peroxide selectivity.

The electropositive F1 centre behaves in an entirely different manner. It binds molecular oxygen directly at the vacancy site, and the interaction is strong enough to cleave the O–O bond, committing the reaction to the four-electron pathway. In the process, the F1 centre itself is quenched, its paramagnetic signature disappearing as the reaction proceeds. Density functional theory calculations reproduced both behaviours, showing favourable adsorption energetics for O2 at F1 sites and for *OOH at sites electronically modulated by neighbouring F2 centres, and the calculated free-energy landscapes matched the experimentally observed selectivity patterns.

Beyond zirconia, the study carries a broad message for the field. Oxygen vacancies have been invoked to explain catalytic behaviour in ceria, perovskites, cobalt and iron oxides, and countless other systems, but the charge state of those vacancies is rarely controlled or even measured. The authors argue that F-centre charge state should be regarded as an independent design lever, alongside vacancy concentration and position. Because the two charge states can be interconverted by atmosphere control during synthesis, and because in situ electron paramagnetic resonance can now monitor them under working conditions, the toolkit exists to rationally design vacancy chemistry rather than accept whatever defects a preparation happens to deliver.

The work also highlights the power of operando spectroscopy to catch catalysts in the act. Static characterization before and after a reaction can miss the transient electronic exchanges that actually govern selectivity; here, the decisive role of the F2 centre only became visible because its paramagnetism and the Raman signatures of intermediates were tracked simultaneously under electrochemical bias. As the energy transition drives demand for selective, precious-metal-free electrocatalysts for peroxide production, water treatment and chemical synthesis, the ability to dial in defect charge states could prove one of the more consequential ideas to emerge from defect engineering in recent years. What was once an invisible nuance of the oxide lattice has become a switch that chemists can now flip at will.

Subject of Research: Charge-state-dependent oxygen vacancy (F-centre) control of electrocatalytic oxygen reduction selectivity in zirconia

Article Title: F-centre charge state and dynamism govern oxide electrocatalytic selectivity

Article References: Zhang, X., Bukhvalov, D., Su, T., Fang, C., Dai, L., San, S., Duan, H., Wang, Y., Liu, K., Cui, J., Hua, Y., Xue, L., Hou, Z., Zhang, W., Xiong, P., Fu, Y., Sun, J., & Zhu, J. (2026). F-centre charge state and dynamism govern oxide electrocatalytic selectivity. Nature Chemistry. https://doi.org/10.1038/s41557-026-02256-w

Image Credits: AI Generated

DOI: 10.1038/s41557-026-02256-w

Keywords: oxygen vacancies, F centres, zirconia, electrocatalysis, oxygen reduction reaction, hydrogen peroxide, selectivity, electron paramagnetic resonance, vacancy engineering, in situ Raman spectroscopy, defect chemistry, 2e- ORR pathway

The research team, led by Yu-Chieh Wang of National Sun Yat-sen University in Kaohsiung, Taiwan, together with colleagues from clinical and academic institutions in Taiwan and Thailand, focused their analysis on the PM1 fraction, particles with diameters of one micrometer or less. These ultrafine particles are of particular concern because they are small enough to penetrate deep into the lungs, past the body’s normal filtering defenses, and to deposit in the delicate alveolar regions where gas exchange takes place. Size-resolved aerosol samples were collected directly in operating rooms, capturing the real-world conditions in which surgeons, nurses, anesthesiologists and other staff work day after day.

Once collected, the PM1 samples underwent an unusually thorough chemical interrogation. The researchers measured the carbonaceous composition of the particles, distinguishing organic carbon from elemental carbon using established thermal-optical protocols, and quantified the concentrations of polycyclic aromatic hydrocarbons, a class of compounds formed during incomplete combustion that includes well-known carcinogens. They also determined the heavy metal content of the particles using high-resolution inductively coupled plasma mass spectrometry, a technique sensitive enough to detect trace elements at extremely low concentrations. Electrocautery, after all, works by heating tissue and metal electrodes to extreme temperatures, and previous work has shown that the procedure can even liberate molten metal particles from surgical implants.

The most striking findings, however, came from electron paramagnetic resonance spectroscopy, a technique that detects unpaired electrons and is therefore the gold standard for identifying free radicals. The EPR analysis confirmed the presence of persistent free radicals on the surgical particles, a category of long-lived radical species more commonly associated with environmental pollutants such as diesel exhaust, coal fly ash, incense smoke and biomass burning particles. Unlike ordinary free radicals, which react and disappear within fractions of a second, persistent free radicals can survive on particle surfaces for hours, days or longer, traveling intact through the air and into the respiratory tract.

The team went beyond simply detecting these radicals and quantified the intrinsic ability of the surgical aerosols to generate reactive oxygen species in aqueous solution. The ROS-generating capacity of the PM1 fraction was measured at 1.03 × 10¹⁸ ± 1.86 × 10¹⁷ spins per gram, a figure that places surgical smoke squarely within the range of recognized hazardous reference particulate materials. For comparison, the researchers noted that this value lies between those reported for SRM-2786, a fine urban dust standard issued by the US National Institute of Standards and Technology, and coal-fired power plant fly ash, a material whose oxidative toxicity has been extensively documented in laboratory animal studies.

This comparison carries a sobering implication. Environmental health scientists have spent decades establishing that the toxicity of airborne particulate matter correlates poorly with mass alone and much better with chemical reactivity, particularly the oxidative potential of the particles. Regulatory frameworks, however, still largely rely on mass-based metrics. The new results suggest that surgical smoke, which has historically escaped the kind of scrutiny applied to traffic or industrial pollution, deserves to be evaluated by the same reactive chemistry standards. The authors argue explicitly that surgical smoke should be regarded as a chemically reactive aerosol rather than an inert particulate contaminant, a reframing with direct consequences for how operating room air quality is monitored and controlled.

The mechanism by which these particles could harm the body follows a well-understood pathway. When inhaled particles carrying persistent free radicals come into contact with the aqueous lining fluid of the respiratory tract, the radicals can catalyze continuous cycles of redox reactions, generating a sustained flux of reactive oxygen species such as hydroxyl radicals and superoxide. These molecules attack lipids, proteins and DNA, triggering inflammatory signaling cascades. Because operating rooms are enclosed spaces with limited air exchange during procedures, and because surgical staff are exposed repeatedly across long careers, the authors warn that sustained inhalation of surgical aerosols may induce severe airway and inflammatory responses, underscoring the need for control measures to mitigate occupational exposure in surgical environments.

The study also situates itself within a growing body of literature on surgical smoke hazards. Earlier investigations have quantified particle concentrations during tonsillectomy and breast surgery, surveyed the inconsistent use of smoke evacuation systems in operating theaters, and catalogued the volatile organic compounds and viruses that can survive in surgical plumes. What distinguishes the new work is its integration of source-focused aerosol chemistry with radical spectroscopy and health risk assessment, providing a mechanistic bridge between what is emitted at the surgical site and what happens once those particles reach human tissue. The researchers describe the reactive aerosols as transient carriers of persistent free radicals that act as continuous sources of reactive oxygen species upon interaction with aqueous environments such as respiratory tract lining fluid.

The practical implications for hospitals are significant. Smoke evacuation systems, high-filtration respiratory protection and adequate room ventilation are already recommended by several professional bodies, but compliance remains uneven worldwide, partly because the hazard has been perceived as minor or poorly characterized. By demonstrating that surgical smoke exhibits oxidative potential comparable to regulated combustion pollutants, the study gives occupational health officers a concrete, quantitative basis for treating electrocautery plumes as a genuine respiratory hazard. The authors emphasize that the chemical reactivity of the particles, not merely their mass concentration, should determine how exposure risk is assessed, and that this sustained redox activity is central to understanding the health consequences of chronic exposure.

For the millions of healthcare workers who stand over electrocautery fields every day, the message of this research is clear: the haze that rises from the surgical site is chemically alive in the most unwelcome sense. It carries combustion-derived carcinogens, trace metals and long-lived radicals capable of generating oxidative stress long after the plume has dispersed. As the evidence accumulates, the operating room may come to be seen not as a pristine clinical environment with an occasional smoky inconvenience, but as an occupational setting with an air quality problem that demands the same rigor applied to factories, highways and power plants. The study was supported by the National Science and Technology Council, Taiwan, and the authors report no competing financial interests.

Subject of Research: Chemical characterization and health risks of electrocautery surgical smoke aerosols in operating rooms

Article Title: Emission characteristics of electrocautery surgical smoke in the operating room: polycyclic aromatic hydrocarbons, metals, persistent free radicals, reactive oxygen species generation, and health risk assessment

Article References: Wang, Y.-C., Ching, W.-C., Wang, C. C., Lee, C.-L., Khemawoot, P., & Ching, W.-M. (2026). Emission characteristics of electrocautery surgical smoke in the operating room: polycyclic aromatic hydrocarbons, metals, persistent free radicals, reactive oxygen species generation, and health risk assessment. Air Quality, Atmosphere & Health, 19(9), Article 206. https://doi.org/10.1007/s11869-026-02095-1

Image Credits: AI Generated

DOI: 10.1007/s11869-026-02095-1

Keywords: surgical smoke, electrocautery, persistent free radicals, reactive oxygen species, PM1, polycyclic aromatic hydrocarbons, heavy metals, operating room, occupational exposure, electron paramagnetic resonance, oxidative stress, air quality