Catalytic activity of platinum nanoparticles on highly boron-doped and 100-oriented epitaxial diamond towards HER and HOR

Platinum nanoparticles supported on boron-doped single-crystalline diamond surfaces were used as a model system to investigate the catalytic activity with respect to the influence of particle morphology, particle density and surface preparation of the diamond substrates. We report on the preparation, characterization and activity regarding hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) of these Pt/diamond electrodes. Two kinds of diamond layers with boron doping above 10²⁰ cm^-3 were grown epitaxially on (100)-oriented diamond substrates; post-treatments of wet chemical oxidation and radio frequency (rf) oxygen plasma treatments were applied. Electrochemical deposition of Pt was performed using a potentiostatic double-pulse technique, which allowed variation of the particle size in the range between 1 nm and 15 nm in height and 5 nm and 50 nm in apparent radius, while keeping the particle density constant. Higher nucleation densities on the plasma processed surface at equal deposition parameters could be related to the plasma-induced surface defects. Electrochemical characterization shows that the platinum particles act as nanoelectrodes and form an ohmic contact with the diamond substrate. The catalytic activity regarding HER and HOR of the platinum nanoparticles exhibits no dependence on the particle size down to particle heights of ∼1 nm. The prepared Pt on diamond(100) samples show a similar platinum-specific activity as bulk platinum. Therefore, while keeping the activity constant, the well-dispersed particles on diamond offer an optimized surface-to-material ratio.