Thermal Activation under Electrochemical Conditions: CO and N2 Bond Dissociation on Co(B5)

In aqueous electrocatalytic environments, the protonation of stable *CO and *N2 to *COH/*CHO and *NNH is fundamentally challenged by the competing hydrogen evolution reaction (HER). In this context, direct dissociation of these molecules offers an alternative pathway, forming reactive *C or *N fragments that can be reduced further if surface bonding is not too strong. However, the strong C≡O and N≡N bonds make dissociation challenging under ambient electrochemical conditions, and the extent to which solvent, local field, and electrolyte ions can promote bond dissociation remains unclear. In this work, we quantify these dissociation pathways at a Co(B5) step site using density functional theory, implicit-solvent calculations, and explicit-solvent calculations using enhanced sampling with machine-learned interatomic potential (MLIP). Implicit-solvent calculations reveal only weak sensitivity to dielectric constant, dipole moment, and solvent radius, with barrier variations typically ≤0.1 eV. In contrast, the local H-bonding network in explicit-solvent simulations lowers the dissociation barrier by ∼0.3 eV relative to vacuum by stabilizing the dissociating atoms. Across different solvents and aqueous solutes, the barrier correlates qualitatively with hydrogen-bond donor strength, pKa, and the local H-coordination number near the transition-state region. Interfacial cations (Li+ and Cs+) modify the work function but do not significantly change the dissociation barrier compared with pure water, suggesting that solvent-mediated interactions dominate under the studied conditions.