Synthesis and Electrocatalytic Hydrogen Evolution Performance of Ruthenium Complexes Constructed With Terpyridine Carboxylic Acid

Three novel ruthenium complexes (Ru1–Ru3) were synthesized from RuCl 3 , terpyridine carboxylic acid, and auxiliary ligands PPh 3 , DPPPy, or H 2 dcbpy, and characterized by single‐crystal X‐ray diffraction (SC‐XRD), elemental analysis (EA), infrared spectroscopy (IR), and ultraviolet‐visible (UV–vis) spectroscopy. The hydrogen evolution reaction (HER) performance of Ru1 and Ru2 was evaluated in alkaline, neutral, and acidic electrolytes. Ru2 exhibited the best activity in 1.0 mol L −1 KOH, with an ECSA of 47.5, η 10 of 380 mV, Tafel slope of 375.6 mV dec −1 , and turnover frequency (TOF) of 97.7 h −1 at 475.6 mV overpotential. Density functional theory calculations revealed that the DPPPy ligand in Ru2 narrows the gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied orbital (LUMO) (2.90 vs. 3.21 eV), raises the HOMO level (−5.28 vs. −8.22 eV), and increases the positive charge on Ru (+0.173 vs. +0.063), thereby promoting electron transfer and hydride formation. This work demonstrates that ligand engineering provides a rational strategy for designing efficient molecular ruthenium electrocatalysts for hydrogen evolution.