The nonadiabatic PCET theory was used to calculate the PCET rate (Eq. 2). For the PCET calculations, the calculations of the electronic coupling and the reorganization energy follow the same protocol as for the ET reactions. Δ𝐺 𝜇𝜈 means the reaction free energy with the donor-proton in the vibrational state 𝜇 and acceptor-proton in the vibrational state 𝜈. 𝑃 𝜇 is the Boltzmann population of the donor-proton in the vibrational state 𝜇 . 𝑆 𝜇𝜈 is the overlap integral between the donor-proton and acceptor-proton vibrational wavefunctions in the states 𝜇 and 𝜈, respectively. 𝑆 𝜇𝜈 is a function of 𝑅 PT , which is the donor-accepter distance. Morse potentials were used to model the donor-proton and acceptor-proton vibrations. In the PCET calculations, the donorhydrogen and acceptor-hydrogen vibrational states up to the third excited states (with 𝜇 max = 3 and 𝜈 max = 3) were taken into account to ensure the convergence. Further details about the calculations of ET and PCET rates are shown in the SI.