Fabrication Of Nitrogen-doped, Boron-doped Diamond Electrodes And Their Performance For Electrocatalytic Oxidation And Reduction

Electrochemical technology is an important water treatment method due to its rapid reaction rate, mild reaction conditions and low apparatus cost, etc. It is well known that the electrocatalytic material has a crucial effect on electrocatalytic ability. Currently, most of the electrode materials suffer from low electrocatalytic activity, high cost or high energy consumption, which hinders the application of electrochemical technology. Therefore, a cost-effective electrode material with high electrocatalytic activity is actively pursued. As an important metal-free electrode material, doped diamond electrodes exhibit superior electrochemical properties. They possess a wide potential window, low voltammetric background current, superior mechanical and electrochemical stabilities, indicating that doped diamond may be promising materials for electrocatalysis. The electrochemical properties of doped diamond can be tuned by varying its chemical composition. B-doped diamond (BDD) has been widely confirmed to be an excellent anode material with an outstanding electro-oxidation activity, while less research focused on the electrocatalytic performance of nitrogen-doped diamond (NDD) electrode. However, NDD electrode exhibits more negative hydrogen evolution potential than most reported cathode materials, which indicates it may be an ideal electrode material for electrochemical reduction. In this paper, we have successfully prepared NDD and BDD electrodes, compared their eletrocatalytic oxidation and reduction activity, and then investigated the electrocatalytic performance of NDD electrode for environment priority pollutant reduction.The main researches and conclusions were as follows:(1) Microwave plasma chemical vapor deposition system was used to prepare the NDD and BDD film on a titanium sheet using methane as carbon source, N2and B2H6as dopant respectively. SEM characterization revealed that the film was uniform and continuous without any obvious cracks. Raman spectrum and XRD pattern demonstrated the formation of diamond film. Moreover, the Nls XPS spectrum of NDD film illustrated that nitrogen atoms have been incorporated into the diamond lattice, and the content of nitrogen is1.96at%.(2) The electrocatalytic oxidation and reduction activity of BDD and NDD was evaluated through2-chlorophenol degradation. The results showed that BDD electrode exhibited higher electro-oxidation activity and NDD electrode exhibited superior electro-reduction activity. (3) To investigate the electro-reduction activity of NDD electrode, nitrobenzene was chosen as the probe compound. The effects of potential, electrolyte concentration and pH on nitrobenzene reduction and aniline formation efficiencies were studied. The results showed that NDD exhibited high electrocatalytic activity and selectivity for reduction of nitrobenzene to aniline. The nitrobenzene removal efficiency and aniline formation efficiency were96.5%and88.4%under optimal conditions, respectively; these values were1.13and3.38times higher than those of graphite electrodes. Coulombic efficiencies for nitrobenzene removal and aniline formation were4.70and16.6times higher than those of graphite electrodes under identical conditions. LC-MS analysis revealed that the dominant reduction pathway on the NDD electrode was nitrobenzeneâ†'nitrosobenzeneâ†'phenylhydroxylamineâ†'aniline. These results indicate that NDD is a promising cathode material for processes relating to electrochemical reduction such as electrochemical degradation, conversion, synthesis and detection.