Electrocatalytic reduction of Cr(VI) on gold-based electrodes in acidic medium: A systematic approach to chromium detection

In the present research, gold immobilized on different substrates (Au, GC, Pt) was examined to fabricate a Cr(VI) sensor in an acidic medium via reduction reactions. Comparative analysis revealed that Au-Pt electrode exhibited better electrocatalytic activity towards the reduction of Cr(VI) compared to Au, Au-Au or Au-GC electrode, which is emphatically discussed in this article. Specifically, the inner α-Au₂O₃ species of Au matrix on the catalytic surface played a key role in catalyzing Cr(VI) in the acidic medium. Voltammetric investigations revealed that the concerned electrode process is proton-dependent. From hydrodynamic voltammetric studies, it was found that the reduction reaction follows a multistep reaction mechanism with a single electron transfer rate-determining step over the Au-Pt surface. The Cr(VI) reduction reaction follows 1^st order kinetics at the Au-Pt electrode surface, where the standard rate constant (k) was found to be 1.4×10⁻² cm⁻¹. The excellent improvement of reduction current over the Au-Pt surface was exploited in the fabrication of the Cr(VI) sensor. The developed sensor detects Cr(VI) ions with a linear dynamic range of 10 to 130 μM, whereas the sensitivity and limit of detection values are 3.21 μAμM⁻¹cm⁻² and 2.97 μM, respectively. Overall, the findings highlight the promising performance of the Au-Pt electrode in detecting Cr(VI) ions and provide valuable insights into the underlying catalytic diagnosis.