Incorporation of Pd Catalyst into Highly Effective Borophene Nanosheet Co-Catalyst for Electrokinetics and Electrochemical Oxygen Reduction Reactions

Abstract To improve the performance of the system, it is of great importance to develop efficient catalysts for ethanol (EtOH) electro-oxidation. Pd/B electrocatalyst was synthesized using a sonochemical method. Structural and electrochemical properties of the prepared nanomaterial were investigated using electrochemical and physical techniques such as Raman spectroscopy, electrochemical impedance spectroscopy (EIS), x-ray diffraction (XRD), zetersizer, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and energy-dispersive x-ray spectroscopy (EDS) and cyclic voltammetry (CV). FTIR confirmed all the functional groups of carbon black, Pd/C, borophene, and Pd/B, and the crystallinity was investigated using XRD. EIS showed that Pd/B has a faster charge transfer and, through investigation using CV, Pd/B showed a more negative onset potential and higher current (−0.76 V vs. Ag|AgCl; 0.07 mA) than Pd/C (−0.65 V vs. Ag|AgCl; 0.05 mA), indicating a more catalytic behavior and tolerance of Pd/B. The active sites could be attributed to the addition of borophene. During the anodic sweeping direction of Pd/B electrocatalyst, it was observed that the ratio of backward peak current ( I bwd ) to forward peak current ( I fwd ), ( I bwd / I fwd ) of in a 2 M of NaOH + 2 M of EtOH is almost equal to ( I bwd / I fwd ) 1 which shows excellent tolerance of Pd/B to poisoning by ethanol intermediate species. The electron transfer rate ( K s ) values for Pd/B at 0.1 M, 0.5 M, 1 M, 1.5 M, and 2 M were estimated to be 4.50 × 10 −13 s −1 , 1.08 × 10 −12 s −1 , 4.28 × 10 −13 s −1 , 5.25 × 10 −14 s −1 and 9.35 × 10 -14 s −1 . At 2 M there is a faster electron transfer than at other concentrations which is also evidenced by the obtained diffusion values ( D ) of the system which were found to be 2.92 × 10 −7 cm 2 s −1 , 4.72 × 10 −8 cm 2 s −1 , 4.82 × 10 −8 cm 2 s −1 , 1.22 × 10 −7 cm 2 s −1 , and 9.12 × 10 −8 cm 2 s −1 . The electrochemically active surface area (ECSA) is strongly related to intrinsic activity, Pd/B (1.85 cm 2 /mg × 10 −5 cm 2 /mg) denotes the highest Pd-O stripping charge than Pd/C (1.13 cm 2 /mg × 10 −5 cm 2 /mg).