  Polycrystalline boron-doped diamond (BDD) is widely used as a working
electrode material in electrochemistry, and its properties, such as its
stability, make it an appealing support material for nanostructures for
electrocatalytic applications. Recent experiments have shown that
electrodeposition can lead to the creation of stable small nanoclusters and
even single metal adatoms on BDD surfaces. We investigate the adsorption energy
and kinetic stability of single metal atoms adsorbed onto an atomistic model of
BDD surfaces using density functional theory. The surface model is constructed
using hybrid quantum/molecular mechanics embedding techniques and is based on
an oxygen-terminated diamond (110) surface. We use the hybrid quantum
mechanics/molecular mechanics method to assess the ability of different
density-functional approximations to predict the adsorption structure, energy
and the barrier for diffusion on pristine and defective surfaces. We find that
surface defects (vacancies and surface dopants) strongly anchor metal adatoms
on vacancy sites. We further investigate the thermal stability of metal
adatoms, which reveals high barriers associated with lateral diffusion away
from the vacancy site. The result provides an explanation for the high
stability of experimentally imaged single metal adatoms on BDD and a starting
point to investigate the early stages of nucleation during metal surface
deposition.
