Highly Dispersed Ru Nanoparticles on Boron‐Doped Ti3C2Tx (MXene) Nanosheets for Synergistic Enhancement of Electrocatalytic Hydrogen Evolution

2D‐layered materials have attracted increasing attention as low‐cost supports for developing active catalysts for the hydrogen evolution reaction (HER). In addition, atomically thin Ti3C2Tx (MXene) nanosheets have surface termination groups (Tx: F, O, and OH), which are active sites for effective functionalization. In this work, heteroatom (boron)‐doped Ti3C2Tx (MXene) nanosheets are developed as an efficient solid support to host ultrasmall ruthenium (Ru) nanoparticles for electrocatalytic HER. The quantum‐mechanical first‐principles calculations and electrochemical tests reveal that the B‐doping onto 2D MXene nanosheets can largely improve the intermediate H* adsorption kinetics and reduce the charge‐transfer resistance toward the HER, leading to increased reactivity of active sites and favorable electrode kinetics. Importantly, the newly designed electrocatalyst based on Ru nanoparticles supported on B‐doped MXene (Ru@B–Ti3C2Tx) nanosheets shows a remarkable catalytic activity with low overpotentials of 62.9 and 276.9 mV to drive 10 and 100 mA cm−2, respectively, for the HER, while exhibiting excellent cycling stabilities. Moreover, according to the theoretical calculations, Ru@B–Ti3C2Tx exhibits a near‐zero value of Gibbs free energy (ΔGH* = 0.002 eV) for the HER. This work introduces a facile strategy to functionalize MXene for use as a solid support for efficient electrocatalysts. Heteroatom boron‐doped Ti3C2Tx (MXene) nanosheets are developed as a solid support to host ultrasmall (2–6 nm) ruthenium nanoparticles. The newly designed electrocatalyst exhibits outstanding performance for electrocatalytic hydrogen production. A combination of first‐principles calculations and electrochemical analysis explains the catalytic mechanism.