Self-Templating Strategies for Transition Metal Sulfide Nanoboxes as Robust Bifunctional Electrocatalysts

Abstract

Hollow nanostructures keep attracting intense interest as multifunctional materials, especially in energy storage and conversion technologies. We introduce a convenient anion exchange method for the synthesis of metal sulfide nanoboxes (NBs) from Co, Co–Fe, and Ni–Fe Prussian blue (PB) nanocubes (referred to as Co–PB, Co–Fe–PB, and Ni–Fe–PB NCs) as templates. Analytical characterizations show that anionic exchange processes between S2– and CN– lead to the formation of metal sulfide nanobox heterostructures (referred to as Co–S@PB, Co–Fe–S@PB, and Ni–Fe–S@PB NBs). The Co–Fe–S@PB NBs were characterized in detail with a wide range of analytical techniques, including X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). Furthermore, postcatalytic XAS and XPS studies indicated that the in situ formation of Co–Fe oxides/hydroxides during the oxygen evolution reaction (OER) provided active species of the Co–Fe–S@PB NBs, while Fe(CN)63– did not play a role in the catalytic activity. Together with their advanced morphology, this resulted in a superior OER performance of the as-prepared Co–Fe–S@PB NBs in comparison with RuO2 and other standards. Co–Fe–S@PB NBs excelled through a low overpotential of 286 mV at 10 mA/cm2, a small Tafel slope value of 37.84 mV dec–1, and high durability over the operational period of 33 h at 10 mA/cm2. Moreover, we applied our strategy to produce new double-layered (Co, Fe)9S8@MoS2 nanoboxes (referred to as Co–Fe–Mo–S NBs). The fine-tuned heterostructured nanoboxes are promising for hybrid electrodes due to their high dual OER and hydrogen evolution reaction (HER) activity throughout the pH range.