Water Splitting with an Enhanced Bifunctional Double Perovskite

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., NdBaMn₂O_5.5, is proposed as a bifunctional electrode material for water electrolysis. Layered NdBaMn₂O_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_0.5Ba_0.5MnO_3-δ as well as NdBaMn₂O_5.5-δ and NdBaMn₂O_5.5+δ (δ < 0.5). Importantly, NdBaMn₂O_5.5 has an OER intrinsic activity (∼24 times) and a mass activity (∼2.5 times) much higher than those of the benchmark RuO₂ at 1.7 V versus the reversible hydrogen electrode. In addition, NdBaMn₂O_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-RuO₂, 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.