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• A Fe/Mn doped cobaltate catalyst was studied experimentally and theoretically. • Binary-dopant intensifies the involvement of lattice oxygen for OER. • The configurational entropy effect may determine the unique property of material. Lattice oxygen-mediated mechanism (LOM) on perovskite oxides for oxygen evolution reaction (OER) process has revealed kinetic superiority over conventional adsorbate evolution mechanism (AEM). However, feasibly enhancing the participation of lattice oxygen is still challenging. Here we designed a perovskite cobaltate (La 0.6 Sr 0.4 Co 0.8 Fe 0.1 Mn 0.1 O 3-δ , LSCFM) nanofiber, and discovered that the co-incorporation of Fe/Mn elements significantly intensifies the involvement of lattice oxygen for OER. Compared with its mono-dopant (Fe or Mn only) counterparts, the LSCFM gives rise to higher surface oxygen vacancies (V o) concentration and faster oxygen ion diffusion coefficient, endowing a small overpotential of 343 mV at 10 mA cm−2 and low Tafel slope of 63 mV dec−1. The strongest pH-dependent activity and metal–oxygen covalency are further unveiled on LSCFM by experimental and theoretical approaches, evidencing that the promoted OER kinetics on LSCFM predominantly stems from the formation of reactive lattice oxygen site. [ABSTRACT FROM AUTHOR]

• The B-site cations in perovskite is manipulated to facilitate water splitting. • The decoration of CoS 2 and oxygen deficiency enhance the catalytic activity. • The evolution of reactive sites was studied by experiments and DFT calculation. The family of perovskite oxides is a promising class of catalysts for diverse energy conversion processes including water splitting. In this work, a facile two-step manipulation (in-situ exsolution and post-sulfurization) strategy was proposed and applied to LaCo 0.2 Fe 0.8 O 3 (LCF) perovskite parent, through which, the electronic state, spatial immersion and intrinsic activity of B-site cobalt (Co) were stepwise tuned at nanoscale proximity accordingly (i.e., lattice Co ions → segregated Co0 → embedded CoS 2). Impressively, the as-prepared catalyst (S-LCF) obtains an emergent oxygen deficient microstructure seamlessly pinned with uniformly distributed CoS 2 nanoparticles (NPs), which demonstrates enhanced performance toward both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), and shows good stability in overall water splitting. The density functional theory (DFT) calculations illustrate the optimized metal-oxygen covalency and hydrogen adsorption Gibbs free energy (ΔG H*) on S-LCF, which further buttresses the prominence of our B-site cation engineering tactics. [ABSTRACT FROM AUTHOR]