Selective atomic layer deposition of RuOx catalysts on shape-controlled Pd nanocrystals with significantly enhanced hydrogen evolution activity

Abstract

The electrochemical hydrogen evolution reaction (HER) is an emerging route for producing clean hydrogen. Recently, Ru-based catalysts have exhibited good activity towards the HER, making them attractive substitutes for Pt. However, the HER performance of Ru-based catalysts still cannot reach the same level as that of commercial Pt/C in acid solution. The atomic layer deposition (ALD) technique has proved to be an effective route for the preparation of noble metal catalysts on substrates. Herein, we successfully deposited RuO_x catalysts on octahedral and cubic Pd seeds through an ALD process. Interestingly, we found that RuO_x was selectively deposited on Pd particles when Pd/nitrogen-doped carbon nanotubes (NCNTs) were used as the substrate. Importantly, the as-prepared Pd@RuO_x/NCNT showed comparable activity with state-of-the-art commercial Pt/C catalysts for the HER. The performance exceeds all of the current Ru-based nanocatalysts for the HER in acid solution. The X-ray absorption spectroscopy and X-ray photoemission spectroscopy analyses indicated that the RuO_x shell consists of metallic Ru and Ru(IV). Density functional theory calculation results indicated that the Gibbs free energy of the intermediate state H* of octahedral Pd@RuO_x was much lower than that of cubic Pd@RuO_x, which resulted in the superior HER activity. This paper provides an example for the rational design of efficient catalysts through a combination of shape-controlled synthesis and the ALD technique.