A perfect match: Silver deposition is one of the fastest electrochemical reactions, even though the Ag(+) ion loses more than 5 eV solvation energy in the process. This phenomenon, an example of the enigma of metal deposition, was investigated by a combination of MD simulations, DFT, and specially developed theory. At the surface, the Ag(+) ion experiences a strong interaction with the sp band of silver, which catalyzes the reaction.

The deposition of Cu(2+) and Zn(2+) from aqueous solution has been investigated by a combination of classical molecular dynamics, density functional theory, and a theory developed by the authors. For both cases, the reaction proceeds through two one-electron steps. The monovalent ions can get close to the electrode surface without losing hydration energy, while the divalent ions, which have a stronger solvation sheath, cannot. The 4s orbital of Cu interacts strongly with the sp band and more weakly with the d band of the copper surface, while the Zn 4s orbital couples only to the sp band of Zn. At the equilibrium potential for the overall reaction, the energy of the intermediate Cu(+) ion is only a little higher than that of the divalent ion, so that the first electron transfer can occur in an outer-sphere mode. In contrast, the energy of the Zn(+) ion lies too high for a simple outer-sphere reaction to be favorable; in accord with experimental data this suggests that this step is affected by anions.

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Cation modulation engineering is employed to tune the intrinsic activity and electronic structure of electrocatalysts for water electrolysis. Here, we designed two-dimensional cobalt–iron-layered double-hydroxide (CoFe-LDH) ultrathin nanosheets by pulsed laser ablation in an aqueous medium. The CoFe-LDH nanosheets exhibited abundant electrochemically active sites and a large surface area. The optimal Co0.5Fe0.5-LDH exhibited a low overpotential of 270 mV during half-cell oxygen evolution reactions (OERs), whereas Co0.25Fe0.75-LDH delivered 365 mV at 10 mA/cm2 during hydrogen evolution reactions (HERs). The bifunctional electrocatalyst exhibited an outstanding water electrolyzer performance at a cell voltage of ∼1.89 V at 10 mA/cm2 and admirable stability for long-run repetitive cycles. The synergistic effect between the modulated cations resulted in better conductivity, and the mass transfer facilitated the HER and OER. We demonstrated that this facile approach can facilitate the engineering of a highly stable and efficient electrode for renewable electrochemical energy conversion reactions.

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