[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.