Water Splitting with Cobalt-incorporated Ruthenium Sulfide (CoxRuS) and a Molecular Cobalt Porphyrin

Abstract

Here we present a one-step synthesis of bimetallic cobalt ruthenium sulfide on Vulcan XC-72R carbon (C-CoₓRuS) for electrochemical water splitting, which was coupled with CoTcPP (cobalt 5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin) for improved Oxygen Evolution Reaction (OER) electrocatalysis. Electrochemical analyses reveal that increasing cobalt content enhances the maximum current density by 8x for HER and 3x for OER. The optimized C-Co4RuS catalyst demonstrates bifunctional activity with an HER overpotential of -75 mV (vs. RHE) at 10 mA cm^-2 and a Tafel slope of 75 mV dec^-1 for HER (Volmer-Heyrovsky mechanism) and an overpotential of 251 mV (vs. RHE) at 10 mA cm^-2 with a Tafel slope of 95 mV dec^-1 for OER. The addition of cobalt to the ruthenium sulfide material facilitates charge transfer and improves active site accessibility according to Electrochemical Impedance Spectroscopy (EIS) and Electrochemical Active Surface Area (ECSA) data. Upon CoTcPP compositing the OER overpotential and Tafel plot decrease to 204 mV (vs. RHE) and 79 mV dec^-1 further improving its catalytic activity. These findings position C-Co_xRuS/CoTcPP as an efficient, bifunctional electrocatalyst, providing a viable alternative to common electrocatalysts for water splitting in sustainable energy applications.