(187j) Strongly Coupled Co@CoOx Nanoparticles and Layered Perovskite As a Highly Stable and Efficient Cathode for Solid Oxide Electrolysis Cells

Due to the increased concern of energy supply and environmental issues, the development of renewable energy technologies with low emissions is urgent.^[1] Hydrogen with the highest specific energy density is considered as the best alternative to fossil fuel towards sustainability of energy.^[2] Solid oxide electrolysis cells (SOECs) have received great attention owing to efficient hydrogen production from electricity at elevated temperature from both thermodynamic and kinetic perspectives, compared to low temperature electrolyzer.^[3] However, conventional Ni based electrode suffers from poor redox-stability and coarsening during steam electrolysis.^[4] Thus, the development of novel fuel electrode materials with high activity and stability is essential for practical application.

In this work, a stable and catalytically active layered perovskite LaBaMn_1.6Fe_0.2Co_0.2O_5+δ (LBMFC) with socketed Co@CoO_x nanoparticles has been fabricated via in situ annealing nominal La_0.5Ba_0.5Mn_0.8Co_0.1Fe_0.1O_3-δ in 5% H₂ at 850 ^oC. A structure transformation (mixed cubic and hexagonal to layered tetragonal phase) and exsolution of core-shell Co@CoO_x has been verified with thermogravimetric analysis, rietveld refinement of x-ray diffraction result and transmission electron microscopy with the energy-dispersive x-ray spectroscopy elemental mapping. The loss of lattice oxygen in this phase transition process leads to an increase of oxygen vacancy in LBMFC, consisting with the high concentration of adsorbed oxygen species, which is beneficial to electrical conduction and catalytic activity. A 300-μm electrolyte supported electrolysis cell with Co@CoO_x decorated LBMFC cathode operated in 10% H₂O-90% H₂ exhibits outstanding current densities of 1135.43, 744.19, 487.79 and 281.43 mA cm^-2 under an applied voltage of 1.3 V at 800, 750, 700, 650 ^oC, respectively. Relevant hydrogen production rate of 511 ml cm^-2 h^-1 calculated from the Faraday’s law has been achieved under an electrolysis voltage of 1.3 V, and the cell polarization resistance is as low as 0.125 Ω cm² under open circuit voltage at 800 ^oC. Moreover, the SOEC with LBMFC as cathode shows remarkable stability over 200 hours at a constant electrolysis current of -200 mA cm^-2, and the in situ exsolved Co nanoparticles are still embedded on the surface of the LBMFC framework without agglomeration observed by scanning electron microscopy, which suggests the strong connection between the exsolved nanoparticles and matrix. The increased oxygen vacancies together with the in situ exsolved high catalytic active Co@CoO_x on the perovskite backbone generate sufficient active sites and consequently improves the performance and stability of LBMFC for the steam electrolysis.