Highly efficient catalysts of ruthenium clusters on Fe3O4/MWCNTs for the hydrogen evolution reaction

Abstract

Producing molecular hydrogen (H₂) using water provides a sustainable approach for developing clean energy technologies. Herein, we report highly active ruthenium (Ru) clusters supported on iron oxide (Ru/Fe₃O₄) and Fe₃O₄/multi-walled carbon nanotubes (Ru/Fe₃O₄/MWCNTs) by simple electrochemical deposition in a neutral aqueous medium. The supported catalyst exhibits good hydrogen evolution reaction (HER) activity in an acidic environment. Cyclic voltammograms (CVs) of potassium ferrocyanide (K₄[Fe(CN)₆]) confirm that MWCNTs enhance the electron transfer process by decreasing the redox formal potential. The overpotentials of Ru/Fe₃O₄/MWCNTs and Ru/Fe₃O₄ electrocatalysts versus the reversible hydrogen electrode (RHE) were found to be 101 mV and 306 mV to reach a current density of 10 mA cm⁻². As prepared, the catalyst displays good stability and retain its HER activity even after 1000 cycles. Furthermore, the stability of Ru/Fe₃O₄/MWCNTs was studied using the chronopotentiometric (CP) technique for 12 h and found negligible loss in the catalytic activity towards the HER. To explore the role of Ru and underneath MWCNTs in improving the catalytic performance of Fe₃O₄, density functional theory (DFT) calculations were carried out. DFT calculations indicate that the octahedral site of Ru/Fe₃O₄ favors the HER with a low overpotential. However, Ru/Fe₃O₄/MWCNTs are more efficient towards the HER, which could be due to the availability of both octahedral and tetrahedral catalytic sites.