Thermochemical water splitting represents a promising pathway for sustainable hydrogen production, leveraging high-temperature redox cycles to dissociate water into hydrogen and oxygen. Among the materials explored for this process, perovskite oxides such as LaSrMnO₃ (LSM) have garnered attention due to their tunable redox properties, oxygen vacancy dynamics, and potential for enhanced cyclic stability. This article examines the role of oxygen vacancy engineering in perovskite-based thermochemical cycles, contrasts their performance with conventional metal oxides like CeO₂, and evaluates their long-term durability.

Perovskite oxides exhibit a general ABO₃ structure, where A and B are cations of different sizes. The flexibility in cationic substitution allows precise control over oxygen vacancy formation and migration, which are critical for thermochemical water splitting. In LaSrMnO₃, partial substitution of La³⁺ with Sr²⁺ introduces mixed valency in the Mn cations, promoting oxygen non-stoichiometry. The creation and annihilation of oxygen vacancies during redox cycles facilitate the splitting of water molecules. During the reduction step at elevated temperatures (typically 800–1500°C), the perovskite releases oxygen, generating vacancies. In the subsequent oxidation step, steam reacts with the reduced material, filling the vacancies and producing hydrogen.

Oxygen vacancy engineering in perovskites involves optimizing A-site and B-site doping to enhance vacancy concentrations and mobility. For instance, increasing Sr content in LaSrMnO₃ raises the oxygen vacancy density but must be balanced against structural stability. Excessive vacancies can lead to phase segregation or degradation over multiple cycles. Studies indicate that La₀.₇Sr₀.₃MnO₃ achieves a balance, demonstrating competitive hydrogen yields of approximately 5–7 mmol/g per cycle at 1350°C reduction and 800°C oxidation temperatures. The mobility of oxygen vacancies in LSM is facilitated by the Mn³⁺/Mn⁴⁺ redox couple, which enables rapid charge compensation during reduction and oxidation.

Comparatively, CeO₂, a benchmark material for thermochemical water splitting, relies on the Ce⁴⁺/Ce³⁺ redox pair for oxygen vacancy generation. While CeO₂ exhibits high oxygen storage capacity, its hydrogen production is often limited by slower vacancy diffusion rates and lower thermal stability at extreme temperatures. Doped ceria (e.g., Zr-doped CeO₂) improves performance but still lags behind perovskites in terms of tunability. For example, Ce₀.₉Zr₀.₁O₂ yields around 4–5 mmol H₂/g per cycle under similar conditions, with gradual degradation due to sintering. In contrast, perovskites like LSM maintain structural integrity over hundreds of cycles, attributed to their robust crystalline framework and resistance to sintering.

Cyclic stability is a critical metric for thermochemical materials, as industrial-scale applications demand longevity. Perovskites excel in this regard due to their ability to accommodate lattice strain during redox transitions. In LaSrMnO₃, the perovskite structure tolerates significant oxygen non-stoichiometry without phase decomposition, whereas CeO₂ suffers from gradual particle agglomeration and surface area loss. Advanced characterization techniques reveal that LSM retains over 90% of its initial hydrogen production capacity after 500 cycles, while CeO₂-based materials often degrade by 20–30% within 200 cycles. The difference stems from the perovskites’ ability to redistribute strain through cooperative octahedral tilting, a feature absent in fluorite-structured CeO₂.

Material synthesis methods further influence performance. For perovskites, solid-state reaction and sol-gel techniques are common, with the latter offering finer control over stoichiometry and particle size. Nanostructuring LSM has been shown to enhance surface area and vacancy accessibility, boosting hydrogen yields by up to 15%. However, nanopowders face challenges in sintering resistance, prompting research into macroporous or composite architectures. CeO₂, on the other hand, benefits from flame spray pyrolysis or hydrothermal synthesis, but its inherent limitations in vacancy mobility remain a bottleneck.

Kinetic studies highlight the faster redox rates of perovskites compared to CeO₂. The activation energy for oxygen vacancy migration in LSM is approximately 1.2 eV, lower than the 1.5–1.8 eV range for doped ceria. This difference translates to quicker hydrogen production rates, with LSM achieving peak yields within minutes versus tens of minutes for CeO₂. The superior kinetics are attributed to the perovskite’s flexible lattice and electronic conductivity, which facilitate rapid charge transfer during steam oxidation.

Thermodynamic analyses reveal that perovskites operate efficiently across a broader temperature range. While CeO₂ requires extreme reduction temperatures (≥1500°C) for substantial oxygen release, LSM achieves comparable vacancy concentrations at 1300–1400°C, reducing energy input. The oxidation step for perovskites is also more exothermic, lowering the net energy penalty. These factors contribute to higher theoretical efficiencies, with LSM-based systems projected to reach 20–25% solar-to-hydrogen efficiency in optimized cycles, outperforming CeO₂ by 5–7 percentage points.

Environmental and operational considerations further favor perovskites. The lower reduction temperatures reduce thermal stress on reactor materials, extending equipment lifespan. Additionally, perovskites’ resistance to carbon deposition in impure steam streams mitigates a common issue for CeO₂ in industrial settings. However, challenges remain in scaling up perovskite synthesis and ensuring consistent performance across large batches.

In summary, LaSrMnO₃ and related perovskites offer compelling advantages for thermochemical water splitting, particularly in oxygen vacancy engineering and cyclic stability. Their tunable chemistry, rapid kinetics, and structural resilience position them as superior alternatives to CeO₂ in high-temperature hydrogen production. Future research should focus on optimizing doping strategies, scalable synthesis, and reactor integration to unlock their full potential.