Imagine a stainless steal container with an unsealed lid that contains normal air, inside a room containing normal air. Now, pump a steady flow of CO2 in that container, bringing it to positive pressure versus the environment outside. This system (inside the container) should eventually reach a steady state. Let's look at the Oxygen content of the system.
By Fick's law of diffusion, since the partial pressure of O2 outside is greater than inside, O2 should start to seep in until the partial pressure of O2 inside and outside has reached equilibrium.
However, by the second law of thermodynamics, energy should always flow toward the lower entropy system.
In a less theoretical mental model, we can visualize the CO2 exiting the container in a equal manner from the junction of the lid and the container. The flow being faster than the rate of diffusion, even if the partial pressure of O2 in the container has reached zero, I have a hard time imagining how there could be O2 ingress in the container.
Asked in a different way: How would you model O2 ingress of the container in the example ?
EDIT: I am referring to the passage about Fick's law in this book