| Summary: | © 2017 American Chemical Society. The rational design of highly active and durable electrocatalysts for overall water splitting is a formidable challenge. In this work, a double perovskite oxide, i.e., NdBaMn 2 O 5.5 , is proposed as a bifunctional electrode material for water electrolysis. Layered NdBaMn 2 O 5.5 demonstrates significant improvement in catalyzing oxygen and hydrogen evolution reactions (OER and HER, respectively), in contrast to other related materials, including disordered Nd 0.5 Ba 0.5 MnO 3-d as well as NdBaMn 2 O 5.5-d and NdBaMn 2 O 5.5+d (d < 0.5). Importantly, NdBaMn 2 O 5.5 has an OER intrinsic activity (~24 times) and a mass activity (~2.5 times) much higher than those of the benchmark RuO 2 at 1.7 V versus the reversible hydrogen electrode. In addition, NdBaMn 2 O 5.5 achieves a better overall water splitting activity at large potentials ( > 1.75 V) and catalytic durability in comparison to those of Pt/C-RuO 2 , making it a promising candidate electrode material for water electrolyzers. The substantially enhanced performance is attributed to the approximately half-filled e g orbit occupancy, optimized O p-band center location, and distorted structure. Interestingly, for the investigated perovskite oxides, OER and HER activity seem to be correlated; i.e., the material achieving a higher OER activity is also more active in catalyzing HER.
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