B-site doping regulates oxygen vacancy assisted water splitting on LaCoO₃ perovskite surfaces: A first-principles study

Thermochemical two step water splitting is a viable route for solar driven hydrogen production based on metal oxide redox cycles. Given the promising hydrogen production efficiency of Ga doped LaCoO₃ reported in experimental studies, Ga doped LaCoO₃ serves as a baseline for exploring alternative B site dopants. Here, density functional theory calculations were performed to compare Ga, Cr, Ti, Zr, and Nb doped LaCoO₃ surfaces and to clarify how B site chemistry affects vacancy assisted H₂O activation, H migration, and oxygen redistribution. H₂O dissociation is thermodynamically favorable on oxygen vacancy surfaces for all doped systems, whereas the subsequent H migration step is much more demanding. The H migration barriers decrease from 3.40 and 2.90 eV for Ga and Cr to 2.65 eV for Ti and about 2.50 eV for Zr and Nb, indicating that H migration is the main energetic limitation. Electronic structure analysis indicates closer Co 3d and O 2p alignment in Ga and Cr, while transition state bonding analysis more directly explains the different H migration barriers. The preferred oxygen migration paths show barriers below 0.3 eV, suggesting accessible near surface oxygen redistribution. Ab initio molecular dynamics (AIMD) simulations at 1100 K show dopant dependent local structural responses after H₂O dissociation, with Nb exhibiting persistent differentiation among its local Nb–O coordination distances. Overall, Ti, Zr, and Nb exhibit lower H migration barriers than the Ga doped baseline, while Nb also shows a distinct local coordination response at high temperature. The differences in surface electron transfer, H migration energetics, and near surface oxygen mobility provide guidance for designing Co based perovskite oxygen carriers for thermochemical water splitting.