Electrocatalytic oxidation and flow injection analysis of formaldehyde at binary metal oxides (Co₃O₄–NiO and CuO–Co₃O₄) modified pencil graphite electrodes

In this work, a highly efficient performance of bimetallic thin films as their oxide forms (Co₃O₄–NiO and CuO–Co₃O₄) modified on pencil graphite electrodes (PGEs) was presented for electrocatalytic oxidation of formaldehyde. In addition, a sensitive and selective amperometric determination of formaldehyde in flow injection analysis system have been first performed using binary transition metal oxides modified PGEs. Co₃O₄–NiO and CuO–Co₃O₄ films were electrochemically deposited on the PGE surface using cyclic voltammetric procedures. The recorded cyclic voltammograms in the presence of formaldehyde in 0.10 M NaOH containing 0.10 M KCl showed that the prepared binary transition metal oxides modified PGEs exhibited a higher electrocatalytic activity than single metal oxide thin films modified PGEs towards oxidation of formaldehyde. The linear responses based on electrocatalytic oxidation of formaldehyde were determined as 2.5–5000 μM and 0.25–1000 μM for Co₃O₄–NiO/PGE and CuO–Co₃O₄/PGE, respectively. Moreover, limit of detections and sensitivities were estimated as 0.73 μM and 81.8 μA mM⁻¹ cm⁻² and 0.09 μM and 166 μA mM⁻¹ cm⁻² for Co₃O₄–NiO/PGE and CuO–Co₃O₄/PGE, respectively. The results from real sample studies proved that the fabricated FI-amperometric sensors enable high applicability towards determination of formaldehyde in real water samples. Graphical abstract: