Comments on the article "Calculation of the electric potential and surface oxygen ion density for planar and spherical metal oxide grains by numerical solution of the Poisson equation coupled with Boltzmann and Fermi-Dirac statistics" (Sensors and Actuators B: Chemical, 293 (2019) 31-40)

The article by Barami, and Ghafarinia (Sensors and Actuators B: Chemical, 293 (2019) 31-40) considers the electric potential and surface oxygen ion density in metal oxide grains. However the problem was solved using the wrong assumptions. Specifically, the density of ionized (positively charged) donors along the nanoparticle radius was assumed to be constant, equal to the density in the massive semiconductor, and the concentration of negatively charged oxygen ions on the surface of the nanoparticle was chosen arbitrarily. The implication of the assumptions are discussed and suggestions are made for the correct approach.