To develop highly stable and active Ru complex catalysts for CO₂ hydrogenation, we synthesized Ru complexes bearing rigid pincer-type tridentate NNN (pyrazole-pyridine-pyrazole) ligands and weakly coordinated triphenylphosphine (PPh₃) ligands. The NNN ligands can strongly chelate with the Ru metal center, contributing to the overall robustness of the catalytic system. Meanwhile, PPh₃ can easily dissociate to form vacant coordination sites, thereby enhancing catalytic activity. As a result, the Ru(Ⅱ)-NNN complex [Ru(L-NNN)Cl(PPh₃)₂]Cl (1, L-NNN=2,6-bis(5-methyl-1H-pyrazol-3-yl)pyridine) was not only quite stable, but also showed high activity for CO₂ hydrogenation to formate, achieving a TON of up to 150 000. In the mechanism study, based on the results of in-situ NMR, in-situ HPLC-HRMS spectra, and density functional theory calculations, it is speculated that the active intermediates with empty coordination sites are highly active species in CO₂ hydrogenation.

Binary composites (ZIF-67/rGO) were synthesized by one-step precipitation method using cobalt nitrate hexahydrate as metal source, 2-methylimidazole as organic ligand, and reduced graphene oxide (rGO) as carbon carrier. Then Ru³⁺ was introduced for ion exchange, and the porous Ru-doped Co₃O₄/rGO (Ru-Co₃O₄/rGO) composite electrocatalyst was prepared by annealing. The phase structure, morphology, and valence state of the catalyst were analyzed by X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). In 1 mol·L^-1 KOH, the oxygen evolution reaction (OER) performance of the catalyst was measured by linear sweep voltammetry, cyclic voltammetry, and chronoamperometry. The results show that the combination of Ru doping and rGO provides a fast channel for collaborative electron transfer. At the same time, rGO as a carbon carrier can improve the electrical conductivity of Ru-Co₃O₄ particles, and the uniformly dispersed nanoparticles enable the reactants to diffuse freely on the catalyst. The results showed that the electrochemical performance of Ru-Co₃O₄/rGO was much better than that of Co₃O₄/rGO, and the overpotential of Ru-Co₃O₄/rGO was 363.5 mV at the current density of 50 mA·cm^-2.