[Ru(tmphen)3]2[Fe(CN)6] and [Ru(phen)3][Fe(CN)5(NO)] complexes and formation of a heterostructured RuO2–Fe2O3 nanocomposite as an efficient alkaline HER and OER electrocatalyst

Abstract

Water electrolysis is one of the most capable processes for supplying clean fuel. Herein, two novel ionic Ru(II)–Fe(II) complexes, [Ru(tmphen)₃]₂[Fe(CN)₆] and [Ru(phen)₃][Fe(CN)₅(NO)], where tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline and phen = 1,10-phenanthroline, were synthesized and characterized by UV-Vis spectroscopy, elemental analysis, FT-IR, and single-crystal X-ray structural analysis. By thermally decomposing the [Ru(tmphen)₃]₂[Fe(CN)₆] complex at 600 °C for 4 h, a heterostructured RuO₂–Fe₂O₃ nanocomposite was fabricated through a facile one-pot treatment and then characterized by FT-IR, XRD, FT-Raman, UV-Vis (DRS), ICP-OES, FE-SEM, TEM, TGA/DTG, BET, and XPS analyses, which revealed the formation of highly crystalline RuO₂–Fe₂O₃ nanoparticles with an average size of 8–12 nm. The prepared nanocomposite was an efficient heterostructured electrocatalyst for performing water-splitting redox reaction processes, including hydrogen and oxygen evolution reactions (HER and OER) in alkaline solutions. In this regard, RuO₂ and Fe₂O₃ samples were also prepared through thermal decomposition of [Ru(tmphen)₃](NO₃)₂ and K₄[Fe(CN)₆] precursors, respectively, as control experiments to compare their HER and OER electrocatalytic activity with that of the RuO₂–Fe₂O₃ nanocomposite. Specifically, the RuO₂–Fe₂O₃ nanocomposite exhibited significant electrocatalytic performance, generating 10 mA cm⁻² current density at −148 and 292 mV overpotentials, and the Tafel slope results from fitting the LSV curves to the Tafel equation were −43 and 56.08 mV dec⁻¹ for the HER and OER, respectively. Therefore, the heterostructured RuO₂–Fe₂O₃ nanocomposite can be viewed as a bi-functional electrocatalyst for HER and OER because it exploits the synergistic effects of heterostructures and active sites at its interface.