Excellent Electrocatalytic Oxygen Evolution Reaction by Non-Noble Metal-Based 3D Perovskite Oxides Ba3–xSrxMTiSbO9 (x = 1, 1.5 for M = Co and x = 2 for Mn/Co)

The large-scale production of green hydrogen from water electrolysis is hindered due to the higher overpotential required for oxygen evolution reaction (OER). While commercial use of noble metal oxide OER catalysts suffer from poor stability and cost ineffectiveness, the development of non-noble metal-based OER catalysts is still a challenge to overcome. The compositional and structural flexibility of 3D perovskite oxides presents a distinct opportunity to design electrocatalysts that can overcome the kinetic sluggishness of OER and address its associated limitations. Herein, we have designed and synthesized a series of 3D perovskite catalysts, Ba3–xSrxMTiSbO9 (x = 1, 1.5 for Co and x = 2 for Mn/Co), by the conventional solid-state method. The Co analogues exhibit exceptional OER performance when compared with the manganese counterpart and a similar or comparable overpotential at 10 mA/cm2 (η10) but with a significantly lower overpotential at 100 mA/cm2 (η100) as compared to RuO2, benchmark electrocatalysts for OER. The Co compounds have also shown superior kinetics as compared to RuO2. The charge-transfer resistance across interfaces measured by operando electrochemical impedance spectroscopy at different potentials follow the activity order of the compounds. The higher electrocatalytic activity of Ba3–xSrxCoTiSbO9 originates from higher d-electron counts, close to unity filling of the eg-orbital electrons, structural factor, μ/t (μ = perovskite B-cation to O2– radius ratio and t = tolerance factor), and higher lattice oxygen participation. A plausible mechanism is also provided based on the pH-dependent OER study. The Co perovskite with the highest lattice oxygen participation and lowest μ/t exhibited the highest OER activity and fastest kinetics. The study demonstrates a nonconventional tool of A-cation manipulation in synthesizing non-noble metal-based 3D perovskites as efficient OER electrocatalysts despite the elusive nature of their active sites.