Ruthenium nanoparticles on covalent triazine frameworks incorporating thiophene for the electrocatalytic hydrogen evolution reaction

Abstract

In this study, 2 to 4 nm ruthenium nanoparticles (Ru-NPs) were loaded (21 to 33 wt%) by decomposition of triruthenium dodecacarbonyl, Ru₃(CO)₁₂, through microwave heating on the prototypal CTF-1 and on thiophene-containing CTFs to access the influence of the thiophene content on the electrocatalytic properties in the hydrogen evolution reaction (HER). The CTFs were synthesized ionothermally with heating at 400 °C and 600 °C (CTF_400/600) using thiophene- (Th-CTF), phenylthiophene- (PhTh-CTF), bithiophene- (BTh-CTF) or quaterthiophene- (QTh-CTF) dinitrile precursors. The homogenous nature of the Ru/CTF composite materials was confirmed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDX). X-ray photoelectron spectroscopy (XPS) revealed the successful introduction of thiophene units and the deposition of Ru-NPs. The Ru/CTF composite materials retained their porosity with calculated Brunauer–Emmett–Teller (BET) surface areas being between 540 to 1326 m² g⁻¹. Low overpotentials and Tafel slopes towards HER down to 30 mV at 10 mA cm⁻² and 55 mV dec⁻¹ were recorded in 0.5 mol L⁻¹ H₂SO₄ with the lowest (i.e. best) value observed for Ru/BTh-CTF_600. Notably, Ru/CTF composite materials based on CTFs synthesized at 600 °C are generally superior compared to the ones at 400 °C by exhibiting lower overpotentials due to more pronounced carbonization during synthesis. In 1 mol L⁻¹ KOH the Ru/CTFs demonstrate even lower overpotentials down to 3 mV with Ru/PhTh-CTF_600 and Ru/QTh-CTF_600 as the two best materials. Tafel slopes down to 39 mV dec⁻¹ indicate fast kinetics. Durability tests of Ru/BTh-CTF_600, Ru/PhTh-CTF_600 and Ru/QTh-CTF_600 with 2000 voltammetry cycles show minor to no alterations in the electrocatalytic performances.