N,S-doped Ti₃C₂ MXene quantum dots-anchored metal ruthenium: Efficient electrocatalyst for pH-universal hydrogen...

Electrocatalytic hydrogen evolution reaction (HER) via water splitting is a prospective technology for achieving the sustainable production of hydrogen. So, ruthenium-based electrocatalysts have been extensively studied. However, metallic ruthenium tends to agglomerate due to the high cohesive energy, resulting in decreased HER performance in practical usage. Introducing sufficient support for dispersing and immobilizing ruthenium-based species is a viable way to enhance the utilization efficiency. MXene-based materials with unique surface termination groups, superior chemical stability, high specific surface area and favorable electrical conductivity have received significant attention as low-cost carriers for the development of active catalysts in HER. Herein, nitrogen (N) and sulfur (S) atom-doped titanium carbide (Ti₃C₂) quantum dots (QDs) were successfully synthesized as efficient carriers for anchoring ultra-small ruthenium nanoparticles (NPs) toward electrocatalytic HER. Electrochemical tests reveal that the resultant N,S-Ti₃C₂ QDs/Ru displays superior HER performance with low overpotentials of 28, 25 and 56 mV at 10 mA cm^-2 current density in 0.5 M H₂SO₄, 1 M KOH and 1 M PBS solutions, respectively. Such a low overpotential is comparable to most previously reported non-metallic catalysts, Ru-based electrocatalysts and commercial Pt/C. In addition, N,S-Ti₃C₂ QDs/Ru displays extraordinarily long-term stability over a relatively wide pH range and is indeed a kind of pH-universal catalyst for hydrogen evolution. Furthermore, density functional theory (DFT) calculations demonstrate that the interactions between metal Ru and N,S-Ti₃C₂ MXene QDs effectively regulate the electronic structure of the active site Ru, lowering the energy barrier of the electrocatalytic HER intermediate, thus dramatically enhancing the activity for N,S-Ti₃C₂ QDs/Ru. This work proposes a novel approach to functionalize MXene quantum dots for use as low-cost electrocatalysts with promising practical applications in renewable energy conversion.