Rhodium-Modified Glassy Carbon Electrode as a Promising Electrocatalyst for Oxygen Reduction Reaction in Phosphoric Acid Electrolytes

A low-cost glassy carbon electrode (GCE), modified with minimum amount of noble metal rhodium (Rh) via electrodeposition method can sensibly enhance the electrocatalytic oxygen reduction reaction (ORR) in H₃PO₄ solution (pH∼2.0). The successful Rh electrodeposition was confirmed by using field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron microscopy (XPS). The rotating disk electrode (RDE) technique was used in kinetic investigation to confirm the ORR mechanism followed by the 4e⁻ transfer process, resulting in the production of water as the final product on the Rh-GCE surface. This finding was further supported by rotating ring disk electrode (RRDE) analysis. The transfer coefficient (α) value was determined ∼0.36, indicated the protonation and electron transfer process in the rate-limiting step of the ORR followed a concerted pathway. The exchange current density (j₀) and standard rate constant (k^o) were determined to be 1.09 × 10⁻⁴ A cm⁻² and 2.35 × 10⁻⁴ cm s⁻¹, respectively.