Atomically Embedded Ag via Electrodiffusion Boosts Oxygen Evolution of CoOOH Nanosheet Arrays

Layered cobalt (oxy)hydroxides have received much attention as cost-effective and efficient catalysts for the oxygen evolution reaction (OER) for electrochemical water splitting. Doping with guest cations possessing different oxidation states such as Ag can change the chemistry of conventional transition metal oxides and hydroxides, generating unexpected electrocatalytic performances. However, Ag dopants have been found to easily segregate at the surface of electrocatalysts, which induces deactivation. Here, we fabricated Ag-doped CoOOH nanosheet arrays using electrochemical deposition, followed by a simple electrochemical diffusion approach. Surprisingly, we revealed, through atom probe tomography (APT), secondary ion mass spectroscopy (SIMS), and energy-dispersive spectroscopy (EDS) that Ag atoms are homogeneously distributed without any detectable segregation. The Ag-doped CoOOH exhibits enhanced OER performance in terms of overpotential, both experimentally (256 mV) and theoretically (60 mV). The homogeneously distributed Ag dopants facilitate the phase transformation from Co(OH)(2) to the active phase of CoOOH. Calculations show that Ag doping enhances phase stability of CoOOH and exposed Ag dopants act as active sites by releasing -OH adsorbates.