Modification of boron-doped diamond electrodes with platinum-iridium for carbon dioxide electroreduction

Boron-doped diamond (BDD) is reportedly a good electrode material for the electroreduction of CO₂ to produce formaldehyde with high Faradaic efficiency. In this study, BDD electrodes were modified with a platinum-iridium composite (Pt-Ir). Deposition of Pt-Ir on the surface of BDD was performed by two different methods. One method involved the modification of the BDD surface, wherein terminal-H atoms were substituted with N atoms. The N-terminal BDD was then immersed in a Pt-Ir nanoparticle solution to form Pt-Ir-BDD (1). The Pt-Ir nanoparticles were synthesized from a 3:4 molar ratio mixture of H₂PtCl₆ and K₂IrCl₆ by a hydrothermal method. Characterization of Pt-Ir nanoparticles by using UV-Vis spectrophotometry and Transmission Electron Microscopy (TEM) image showed an absorbance peak at 420 nm with an average particle size of 2.6±0.6 nm. In the second method, Pt-Ir was deposited onto BDD using chemically assisted electrodeposition by applying a reduction potential of -0.5 V (vs. Ag/AgCl) to form Pt-Ir-BDD (2). Scanning Electron Microscope (SEM) images showed that the second method provides better distribution of Pt-Ir on the BDD surface. Furthermore, cyclic voltammetry of CO₂, dissolved in 0.1 M NaCl showed a reduction potentials at -1.7, -1.3, and -1.2 V (vs. Ag/AgCl) at BDD, Pt-Ir-BDD (1) and Pt- Ir-BDD (2), respectively, indicating that modification with Pt-Ir allows the conversion of CO₂ with higher Faradaic efficiency.