Anion-modulated molybdenum oxide enclosed ruthenium nano-capsules with almost the same water splitting capability in acidic and alkaline media

Hydrogen production by water electrolysis is extremely limited by high energy consumption due to high overpotentials, forcing people have to develop catalysts that can efficiently catalyze the water splitting reaction. However, currently most transition metal-based catalysts can only be used in alkaline environments, because most of them are unstable in acidic and highly oxidative environments, as well as single-purposed. Therefore, it is a great challenge to seek for stable bifunctional catalysts with high hydrogen and oxygen evolution reaction (HER&OER) kinetics in wide pH range. Although Ru nanoparticles possess high activity, they easily suffer leaching and oxidation inactivation. To this, a bifunctional Ru@MoO(S)3 nano-capsule structure electrocatalyst applied to the wide pH range is designed and built, in which Ru nanoparticles are harmoniously encapsulated in a sulfur-modulated molybdenum oxide (MoO(S)3) shell. This all-in-one integration allows Ru to retain intrinsic catalytic activity and rapid mass transfer process while preventing Ru from electrochemical oxidation and then guaranteeing recyclability. Specially, Ru@MoO(S)3 drives the water splitting in 0.5 M H2SO4 and 1 M KOH at a current density of 10 mA cm−2 only needs 1.522 V and 1.526 V cell voltage, respectively, with nearly 100 % Faraday efficiency. This is the first report that a catalyst possesses almost the same water splitting activity in acidic and alkaline media, and also significantly surpasses the commercial Pt/C and RuO2 catalyst electrode pairs. In addition, in the 24 h constant current water splitting test, Ru@MoO(S)3 has very small current density decay. This work provides a new insight into design of bifunctional electrocatalysts for efficient pH-wide water splitting. [Display omitted] •Bifunctional Ru@MoO(S)3 nanocapsule catalyst for HER/OER in wide pH range is built.•Nanocapsule structure promotes intrinsic catalytic activity and mass transfer.•Nanocapsule structure avoids electrochemical oxidation of Ru, with high stability.•It only needs 1.522/1.526 V to drive acidic/alkaline water splitting at 10 mA cm−2.•This work is helpful to reduce complexity and cost of practical water electrolysis.