Geometry optimisations, NEB calculations, and frequency analyses were performed within the framework of the Transition State Tools for ReaxFF (see supplementary material A). For an efficient calculation of atomic charges and linear response properties, the atom-condensed Kohn-Sham density functional theory approximated to second order (ACKS2) 4,93 charge equilibration scheme was applied. Energy minimisation of the atomic coordinates was considered converged when all forces were smaller than 2 × 10 -3 eV Å -1 . For NEB calculations, a spring constant of 5.0 eV Å -2 and a convergence criterion of 1 × 10 -2 eV Å -1 were chosen.