Bimetallic CoFe Borides: A New Pathway for the Transformation of Amorphous Borates to Metallic Borides for the Determination of Paracetamol

The development of transition metals as electrode materials that can exhibit good conductivity and fast electron transfer ability through electroactive sites is highly desirable because high sensitivity and selectivity can be achieved. When compared to other nonmetals, boron (B) possesses a lower electronegativity (χB-2.04) than carbon (χC-2.55), nitrogen (χN-3.04), and oxygen (χO-3.44) and thus forms a covalent linkage with electron-rich transition metals (Co or Fe) to form monometallic or bimetallic borides (CoB/FeB or CoFeB). However, the formation of crystalline bimetallic borides using conventional synthesis approaches is highly challenging. In this regard, for the first time in the present work, we developed crystalline bimetallic cobalt–iron boride (CoFeB) with nanostructure features via a chemical reduction and thermal annealing process as an efficient electrode material for the electrochemical detection of paracetamol. After the postannealing process, the obtained amorphous borates (CoFeOBO₃) are transformed into a highly crystalline form composed of bimetallic borides as revealed from X-ray diffraction (XRD) analysis. The resultant CoFeB coated on a screen-printed electrode (SPE) showed well-defined oxidation and reduction peaks with potentials of about E_pa = +0.51 V and E_pc = +0.44 V (vs Ag/AgCl) for paracetamol (pH = 7.2). At an optimized applied potential of +0.60 V (vs Ag/AgCl), a linear i–t response for paracetamol was observed from 0.01 μM to 2.7 mM with a good sensitivity of 64.79 μA mM^–1 cm^–2 and a low detection limit of 3.8 nM. In addition, CoFeB/SPE is found to be tolerable against interference species and shows agreeable repeatability and durability. Based on these results, the present work could develop a facile approach to producing a variety of metallic borides by tuning the composition of various transition elements, where high conductivity and stability are required in various electrocatalytic and electrochemical applications.