A nanoporous diamond particle microelectrode and its surface modification

Boron doped diamond electrode (BDDE) with dimensions of tens of or hundreds of μm has received widespread attention for electrochemical and biological applications because of exceptional features such as wide potential window for water stability, excellent electrochemical/chemical stability, and superior antifouling properties. This work reported a feasible way to fabricate a single nanoporous BDD particle microelectrode (sDPME) using a commercial single-crystal BDD particle (cBDD) as the substrate. The nanoporous surface of cBDD (pcBDD) was formed via thermal catalytic treatment with nickel as the catalyst, followed by further electrodeposition of gold nanoparticles (Au NPs) to fill the nanopores, increasing its electrocatalytic performance. As a comparison, the heavily-doped polycrystalline BDD film was deposited on cBDD via hot-filament chemical vapor deposition, increasing its electrical surface conductivity, followed by the similar thermal etching to form the nanoporous surface (prBDD) as well as Au NPs modification. We gradually characterized surface modification of cBDD using scanning electron microscopy, Raman, energy dispersive spectroscopy and various electrochemical techniques. The results demonstrated that among six sDPMEs, the Au NPs-modified nanoporous sDPMEs (Au/prBDD) have one order of magnitude higher heterogeneous electron transfer kinetic constant than the cBDD. This difference was attributed to synergistic effects of the improved electrical conductivity (with a higher doping level of few 1020 cm−3 versus 1018 cm−3), the improved capability for electron transfer (with lower charge transfer resistance of 1.3 kΩ versus 8.6 kΩ) as well as the increased electrochemically active surface area (1.12 mm2 versus 0.34 mm2).