Proton Transport on Graphamine: A Deep-Learning Potential Study

The performance of proton-exchange membrane fuel cells is critically dependent on the conduction of protons. Conventional proton exchange membranes employ materials such as Nafion that conduct protons only when properly hydrated. If the relative humidity is too low or too high, the fuel cell will cease to operate. This limitation highlights the need to develop new materials that can rapidly conduct protons without the need to regulate hydration. We present detailed atomistic simulations predicting that graphamine, which is an aminated graphane, conducts protons anhydrously with a very low diffusion barrier compared to existing materials. We have constructed a deep-learning framework tailored to modeling graphamine, enabling us to fully characterize and evaluate proton conduction within this material. The trained deep-learning potential is computationally economical and has near-density functional theory accuracy. We used our deep-learning potential to calculate the proton diffusion coefficients at different temperatures and to estimate the activation energy barrier for proton diffusion and found a very low barrier of 63 meV. We estimate the proton conductivity of graphamine to be 1322 mS/cm at 300 K. We show that protons hop along Grotthuss chains containing several amine groups and that the multidirectional hydrogen bonding network intrinsic in graphamine is responsible for the fast conduction of protons.