Multiple Perovskite Layered Lanthanum Nickelate Ruddlesden-Popper Systems As Highly Active Bifunctional Oxygen Catalysts

A systematic study of the Ruddlesden-Popper structured Lan+1NinO3n+1 (n = 1, 2, 3, and 4) and its catalytic performance in oxygen evolution (OER) and oxygen reduction reactions (ORR) is carried out with a view to design a highly-efficient and cost-effective electrocatalyst. In particular, we introduce for the first time a novel La5Ni4O13-delta with a 4-layered perovskite structure (n = 4) for use as a highly active and durable bifunctional oxygen catalyst for OER/ORR. Concretely, La5Ni4O13-delta catalysts has demonstrated performance of 1.65 V at 10 mA.cm(-2) and 0.66 V at near half-wave potential (-3 mA.cm(-2)) for OER and ORR, respectively, this indicates excellent intrinsic OER/ORR kinetics. Furthermore, by controlling the fuel-to-oxidizer ratio (using extremely fuel-rich conditions) in the glycine-nitrate combustion technique, the 4-layered perovskite La5Ni4O13-delta catalysts are synthesized as a single Ruddlesden-Popper phase with various dopants to further boost its bifunctional oxygen electrode activity. Among OER/ORR catalysts, La5Ni3CoO13-delta catalysts exhibit exceptional electrocatalytic activity with low overpotential and Tafel slope (35/76 mV.dec(-1) for OER/ORR). Outstandingly, the La5Ni3CoO13-delta is able to achieve an extremely low overpotential of 370 mV at 10 mA.cm(-2) in 0.1 M KOH for OER, surpassing Ir/C catalysts and any metal oxide catalyst ever reported. The high catalytic performance of La5Ni3CoO13-delta can be attributed to its favorable electronic structure enriched with oxygen defects and electronic charge carriers (increased Ni oxidation state) as well as to the promoted lattice-oxygen oxidation mechanism pathway that comes from strong metal-oxygen covalency (high oxygen-ion diffusion rate).