Why BDD Anode is Not Widely Used in Electrochemical Wastewater Treatment?

Why BDD Anode is Not Widely Used in Electrochemical Wastewater Treatment?

Boron-doped diamond (BDD) is a novel material with distinctive characteristics. BDD was found to be superior in the anodic oxidation of organic compounds over many other anode materials. For example, in a study comparing the ability of BDD and SnO2 anodes towards oxidizing various dyes, the current efficiency on BDD was generally 2-3 times higher than was obtained on SnO2.

The high oxidation ability was associated with high oxygen evolution potential. On BDD, oxygen evolution appeared at 2.7V, compared to 1.9V as obtain on the SnO2 anode. In addition, BDD was found to be very stable. It could sustain nearly 200 hours at a current of 100mA/cm2 without a significant increase in potential, which was superior to SnO2-based anode under the same current density load. A very recent study reported BDD deposited on Ti exceeded 500 hours of operation in a very acidic environment.

To explain the high efficiency towards the anodic oxidation of organic compounds by BDD, a systematic study was conducted recently to compare BDD, PbO2, and SnO2. The authors claimed that the oxidation by PbO2 most likely took place at the surface of the electrode while that by BDD took place in the bulk. They concluded that the hydroxyl radicals were essentially detached from the BDD surface and diffused to the bulk electrolyte as free radicals. Considering that these free radicals had only a few nanoseconds of life in water, they would probably exist within the diffusion layer. The release and transport of the OH∙radical is probably the determinant factor for the oxidation efficiency of BDD electrodes.

Despite the superior performance of the boron doped diamond film, there are a number of difficulties that prevent the widespread use of BDD. It is difficult to find a suitable support material. Conventionally it is prepared on doped silicon. Si is brittle and not nearly as conductive as metals. Commercial BDD is also available in the form of thin films on valve metals including niobium and tantalum, but these metals are inevitably expensive. Titanium is the most desired material as the support for industrial anodes, but the BDD film did not adhere well to titanium.