[Research Highlights] A research team led by Professor Tao Liu at the Hydrogen Science Center, School of Materials Science and Engineering, Shanghai Jiao Tong University, in collaboration with Professor Guangfeng Wei’s team at Tongji University and other research partners, has recently reported a major advance in the design of catalytic interfaces for efficient oxygen evolution reactions. The study, entitled “Unravelling the Key Factors Governing O2 Evolution upon Charging a Reversible LiOH-based Nonaqueous Li||O2 Battery”, was published online in Nature Communications. The study focuses on the oxygen evolution reaction during the charging of Li||O2 batteries employing organic-aqueous hybrid electrolytes. With the central objective of improving the Faradaic efficiency of oxygen evolution reaction (OER FE), the researchers conducted in situ monitoring of key reactive oxygen species, quantitatively identified the origins of parasitic reactions, and systematically examined the relationship between catalytic interfacial properties and oxygen evolution efficiency. The work identifies interfacial hydroxyl species (*OH/·OH) as the principal drivers of organic-solvent decomposition and carbon corrosion. A three-pronged strategy integrating catalyst-site design, electrolyte-solvent optimization, and water-activity control increased the OER FE from approximately 0% to 75% and enabled stable cycling for more than 300 cycles. These findings deepen mechanistic understanding of selectivity control for oxygen evolution reaction in organic-aqueous hybrid electrolytes and provide a practical design pathway toward efficient, stable, high-specific-energy lithium||oxygen batteries. Professors Tao Liu and Guangfeng Wei are co-corresponding authors. The work was supported by the National Natural Science Foundation of China, the Science and Technology Commission of Shanghai Municipality, and national talent programs.
[Background] The oxygen evolution reaction (OER) underpins a wide range of clean-energy and environmental-remediation technologies, including water electrolysis for hydrogen production, carbon dioxide reduction, metal-air batteries, and electrochemical advanced oxidation of selected pollutants. It therefore plays a major role in determining the efficiency and cost of these technologies. OER involves a kinetically sluggish four-electron transfer process and multiple reactive oxygen species, which can readily couple with parasitic reactions at catalytic interfaces, severely compromising reaction selectivity, efficiency, and reversibility. This challenge is particularly acute in organic-aqueous hybrid electrolytes dominated by organic solvents and supplemented with water, such as the electrolytes used in LiOH-based lithium-air batteries, because the concentration of oxidizable organic molecules surrounding surface reactive oxygen species is extremely high. It has therefore remained unclear whether catalytic-interface regulation can steer LiOH decomposition along the desired four-electron OER pathway in such mixed-solution environments. To address this issue, the present study first quantitatively identified the sources of parasitic reactions induced by key reactive oxygen species and then analyzed the structure-performance relationships among catalytic active sites, the solvation environment, and O2 evolution efficiency (Figure 1), thereby elucidating the principles governing enhanced OER selectivity in organic-aqueous hybrid electrolytes.
Figure 1. Schematic illustration of heterogeneous catalytic LiOH decomposition and the central scientific questions governing O2 evolution
[Technical Challenges] Several technical challenges had to be overcome to address the scientific questions above. (1) Real-time monitoring of key reactive oxygen species: LiOH decomposition and O2 evolution during charging may involve multiple oxygen-containing intermediates, including *OH, ·OH, H2O2/HO2−, *OOH, and 1O2. These intermediates are short-lived and highly reactive, and may react rapidly with the electrolyte and electrode interface, placing stringent demands on the sensitivity, selectivity, and temporal resolution of operando characterization methods. (2) Quantitative differentiation of the complex sources of interfacial parasitic reactions: LiOH decomposition and O2 evolution occur at a multiphase interface comprising the catalyst, conductive substrate, electrolyte, and solid LiOH. Electrolyte oxidation, carbon-substrate corrosion, and further decomposition of by-products are intertwined, creating complex parasitic-reaction signals and making it difficult to directly link reactive species and reaction pathways to specific parasitic products. (3) Elucidation of the mechanism controlling O2 evolution reaction selectivity: Catalyst metal sites, electrolyte solvent, water content, and conductive substrate all affect the OER FE, while these factors are also synergistically coupled. Determining the specific contributions of interfacial solvation, OH⁻ transport kinetics, hydroxyl-species generation, and the electronic structure of catalytic sites to the desired O2-evolution pathway and competing parasitic pathways is essential for understanding how reversibility is controlled in LiOH-based systems.
[Strategy and Innovation] To address these challenges, the research team constructed a reversible lithium||oxygen battery using iron-cobalt-nickel layered double hydroxide (FeCoNi-LDH) supported on conductive carbon black as the positive electrode and water-containing sulfolane (TMS) as the hybrid electrolyte. The researchers combined online electrochemical mass spectrometry (OEMS), isotope labeling, chemical titration, in situ ultraviolet-visible (UV-vis) spectroscopy, in situ attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations to monitor reactive oxygen species under operando conditions, quantitatively trace the origins of parasitic reactions, and elucidate the mechanisms governing the OER FE. On this basis, the team proposed a three-pronged synergistic strategy—catalyst-site design, electrolyte-solvent optimization, and water-activity control—offering a new route to improve OER selectivity during LiOH decomposition and enhance battery cyclability.
(1) Identifying the Sources of Parasitic Reactions and Key Reactive Oxygen Species during LiOH Decomposition upon Charging
The study first elucidated the electrochemical processes underlying the charging and discharging of the FeCoNi-LDH/TMS-H2O system. In situ X-ray diffraction (XRD) showed that the discharge product was predominantly LiOH (Figure 2b). During charging, LiOH was progressively decomposed across the first two voltage plateaus (Figure 2a, b), whereas O2 evolution occurred mainly at approximately 3.8 V. The subsequent high-potential plateau was accompanied by CO2 evolution, indicating oxidative decomposition of carbon-containing by-products. Further OEMS measurements using H218O isotopic labeling (Figure 2g) confirmed that the O2 released during charging originated from LiOH decomposition rather than direct electrochemical oxidation of water in the electrolyte.
Figure 2. Product evolution and quantitative attribution of parasitic-reaction sources during FeCoNi-LDH-catalyzed LiOH decomposition
To further elucidate the origins of the carbon-containing by-products, the researchers used a 13C-labeled carbon substrate in conjunction with OEMS to quantitatively distinguish the contributions from carbon corrosion and TMS decomposition. The results (Figure 2e) showed that approximately 65% of the CO2 generated during charging originated from corrosion of the carbon substrate, while approximately 35% arose from decomposition of the TMS electrolyte. Replacing amorphous Super P carbon with a gold substrate reduced CO2 evolution by approximately 65%, further confirming carbon corrosion as one of the principal factors limiting charge reversibility. In situ spectroscopy and Fenton-mimic experiments (Figure 3) showed that LiOH decomposition generated oxygen intermediates including *OH, ·OH, H2O2/HO2−, and potentially *OOH, but did not produce singlet oxygen (1O2). Interfacial *OH preferentially induced carbon corrosion, whereas short-lived ·OH dispersed in solution preferentially attacked the organic solvent. Together, these species promoted the formation of by-products such as Li2CO3, Li2SO3, and Li2C2O4, ultimately increasing polarization and accelerating cycling degradation.
Figure 3. In situ identification of key reactive oxygen species during FeCoNi-LDH-catalyzed LiOH decomposition
(2) Elucidating How the Electrolyte Environment Regulates O2 Evolution and Parasitic Reactions
The electrolyte is not an inert medium; it is a key determinant of LiOH decomposition and OER selectivity. Fukui-index calculations and experimental results (Figure 4a) showed that TMS is more resistant to ·OH-induced oxidation than common ether, amide, and sulfoxide solvents, making it well suited as the primary solvent in LiOH-based electrolytes. Water content regulates the OER FE through two main pathways. On the one hand (Figure 4c–e), interfacial water molecules alter the stability of the *O intermediate under interfacial solvation, thereby modulating both the energy barrier of the OER rate-determining step (RDS) and the formation energy of ·OH. On the other hand (Figure 4f–g), the amount of bulk water restructures the hydrogen-bond network in the TMS-H2O electrolyte, affecting LiOH dissolution and OH− mass-transfer kinetics. Insufficient water limits mass transport and increases polarization, whereas excessive water can disrupt the balance of reaction barriers and intensify parasitic reactions. Consequently, the OER FE exhibits a characteristic volcano-shaped dependence on water content (Figure 4b).
Figure 4. TMS-based electrolyte design and the mechanism by which water content regulates OER selectivity
(3) Elucidating How the Intrinsic Catalyst Structure Governs OER Activity and Selectivity
The study established that the intrinsic structure of the catalyst plays a decisive role in OER activity and selectivity. Multimetallic LDH catalysts displayed markedly higher OER selectivity than single-metal LDHs, with FeCoNi-LDH exhibiting the highest OER FE and the lowest CO2 release (Figure 5a–d). DFT calculations identified the FeCoCo site on the FeCoNi-LDH surface—comprising a central Co atom adjacent to Fe and Co atoms—as the optimal active site. This site combines a lower energy barrier for the OER RDS with a higher ·OH formation energy (Figure 5e, f), thereby promoting the desired O2-evolution pathway while suppressing ·OH generation. Electronic-structure analysis showed that the conduction-band minimum of FeCoNi-LDH is dominated by Co orbitals and that the central Co atom at the FeCoCo site possesses a highly localized electron-accepting state, which facilitates charge transfer during OER. These results indicate that Co serves as the primary active center, while Fe and Ni enhance catalytic activity and selectivity by tuning the local electronic structure of Co. A system combining an FeCoNi-LDH/Au positive electrode with a TMS-H2O electrolyte achieved a FE of approximately 75% (Figure 5g) and remained stable for more than 300 cycles at an areal capacity of 0.5 mAh cm−2.
Figure 5. Effects of intrinsic catalyst structure and the conductive-substrate interface on OER Faradaic efficiency and cycling stability
[Research Significance] This work establishes an integrated research framework encompassing operando identification of key reactive oxygen species, quantitative source apportionment of parasitic reactions, and analysis of structure-performance relationships governing O2-evolution efficiency. It establishes hydroxyl species as the key reactive oxygen species in the electrochemical decomposition of LiOH, demonstrates that hydroxyl-induced carbon corrosion and organic-solvent decomposition are the principal causes of poor OER selectivity, and proposes an interface-optimization strategy that synergistically combines catalyst-site design, electrolyte-solvent optimization, and water-activity control. The study advances the mechanistic understanding of the origins of parasitic reactions and the regulation of OER selectivity in LiOH-based Li||O2 batteries. It also challenges the conventional assumption that high four-electron OER FE is unattainable in organic-solvent-dominated electrolyte environments, providing a viable design pathway toward highly reversible Li||O2 batteries with long cycle life. This research was supported by the National Natural Science Foundation of China, the National Key Research and Development Program of China, and the National High-Level Young Talent Program. Paper link: https://www.nature.com/articles/s41467-026-75284-2.