Overall, DFT calculations reveal that the ECH of AP to 1-PEA is thermodynamically downhill on all the investigated metals under the experimental conditions of this work, and that the most endergonic step in the reaction mechanism is the first hydrogenation to yield *APHᐧ. More specifically, Ni displays the most endergonic hydrogenation towards *APHᐧ, which together with the competing HER explains the very poor ECH performance observed in experiments with this cathode. In the case of Pt, the energy landscape for ECH is feasible at ambient conditions, so we attribute its poor activity to the very strong competition with HER. Lastly, Au, Ag, and Cu exhibit the most favorable energetics (Fig ), in agreement with experimental observations. Additionally, upon H diffusion, which is reported to be facile on fcc metal surfaces, we find that ΔG*APHᐧ on the 0.75 H coverage on Cu is further lowered from +0.49 to +0.39 eV, while no marked improvement is observed on the less dense 0.25 H coverage (see Supplementary Materials). To provide a more detailed understanding of the ECH mechanism on these three electrodes, as well as the potential role of the water solvent in aiding the transfer of adsorbed H atoms, we set out to investigate the reaction kinetics of the most endergonic step (*AP ➝ *APHᐧ) on the 0.25 H coverage of Ag and Au, and on the diffused 0.75 H coverage of Cu. With this aim, the corresponding transition states (TS) connecting the adsorbed *AP and *APHᐧ intermediates were modelled both in the gas phase and in the presence of up to three explicit H2O molecules. Notably, we observe that the calculated energy barriers significantly decrease with the introduction of two waters, which act as a proton shuttle between the metal surface and the physisorbed *AP (inset, Fig. ), while no marked improvement is observed with the addition of the third (see Supplementary Figure ). In particular, the energy barriers decrease by ca. +1.5 eV in the presence of two waters with respect to the calculations in vacuum, highlighting the critical role of the water solvent in promoting ECH. Furthermore, these barriers assisted by two waters, calculated relative to the lowest energy intermediate preceding the TS, are coherent with ECH activity at ambient conditions, i.e. Au (+0.30) < Cu (+0.63) < Ag (+1.02). However, neither the predicted thermodynamic ΔG*APHᐧ values (Au < Ag ~ Cu), nor the kinetic barriers for *AP hydrogenation (Au < Cu < Ag) alone, can fully explain the experimental trends of J1-PEA (Cu > Ag ∼ Au). We rationalize this with the fact that, under reaction conditions, the 0.25 H coverages on Ag and Au are predicted to be in equilibrium with the bare surface, which is deemed to be inactive (Fig. ). On the other hand, the 0.50 H, 0.75 H, and 1.0 H coverages on Cu exhibit similar stabilities and comparable ECH activities according to their associated ΔG*APHᐧ values and the calculated barrier for *AP hydrogenation (see Supplementary Figure ). Altogether, the fact that the most stable coverages of Cu under reaction conditions are deemed to be active towards ECH, while the predicted coverages for Ag and Au are in equilibrium with the inactive bare surface, is consistent with the activity trend observed in experiments. These thermodynamic and kinetic investigations of the different metal surfaces therefore confirm our initial hypothesis on the requirements to promote ECH in alkaline conditions. More specifically, ECH catalysts must promote water dissociation and reduce the generated protons to H atoms while retaining them on the surface with moderate strength to facilitate ECH. The adsorbed hydrogens should also be spaced out on the electrode surface to prevent HER via a Volmer-Heyrovsky mechanism. Finally, our findings also reveal that surface H diffusion can increase the binding of key reaction intermediates, highlighting the importance of the H surface coverage in ECH, as well as its dynamics.