Twinning Enhances Efficiencies of Metallic Catalysts toward Electrolytic Water Splitting

Abstract Twinning is demonstrated to be an effective way of enhancing efficiencies of metallic catalysts toward electrolytic water splitting. Dendritic Cu possessing dense coherent nanotwin (NT) boundaries (NTCu‐5nm) is successfully prepared with an organic‐assisted electrodeposition at high pulse current densities. NT boundaries significantly improve electrocatalytic efficiencies and stability of NTCu‐5nm over nanocrystalline Cu (NCCu), reducing overpotentials at 10 mA cm −2 for the oxygen evolution reaction (OER) from 378 to 281 mV and from 235 to 88 mV for the hydrogen evolution reaction (HER), with a small chronoamperometric decay of 5% after 100 h continuous overall water splitting at an ultrahigh initial current density of 500 mA cm −2 , largely outperforming the large chronoamperometric decay of 27% for only 1 h operation of the NCCu//NCCu couple. The defective twin boundaries enable formation of active Cu III O 2 − at low overpotentials, thus enhancing OER performance. The synergistic geometric and electronic effects induced by the twin boundaries result in shifts in Gibbs free energies of hydrogen adsorption (Δ G H ) toward the apex of a volcano plot of exchange current density versus Δ G H , leading to the remarkable improvement in HER activity.