Control of electric conductivity and electrochemical activity of hydrogenated amorphous carbon by incorporating boron atoms

Highly conductive hydrogenated amorphous carbon with higher resistance to electrochemically induced corrosion was successfully synthesized by incorporating boron atoms and regulating the amount of sp²-bonded carbon with plasma-enhanced CVD method. The structure, electrical properties, and electrochemical reactivity of boron-doped amorphous carbon (B-doped DLC) were investigated. Boron atoms in amorphous carbon acted as an accepter because the conduction of B-doped DLC was p-type. Volume resistivity was 6.36 × 10^-2 ω cm at highly B-doped DLC (B = 1.3 atom%). The highly B-doped DLC films exhibited a wide working potential range over 3 V in an aqueous solution. The kinetics of hydrogen evolution, which determines the working potential range, could be suppressed by decreasing the number of boron atoms incorporated in DLC because B atoms act as an electrochemical catalyst for H₂ evolution. A double-layer capacitance of the highly B-doped films was as low as boron-doped diamond. This is due to the absence of ionizable surface functionalities like -NH₃ and reversible electron transfer kinetics for inorganic redox analytes (Fe(CN)₆^3-/4- and Ru(NH₃)₆^2+/3+), which were on the same level as those of boron-doped diamond. The lower kinetics of O₂ evolution at B-doped DLC enables to observe the redox reaction of Ce3^+/4+ with a standard potential higher than that of H₂O/O₂. Mn ²⁺ ions with a standard potential lower than that of H₂ evolution could also be electrochemically analyzed in the range from 20 μM to 2.5 mMat moderately B-doped DLC with lower kinetics of H₂ evolution.