Engineering Steam Induced Surface Oxygen Vacancy onto Ni-Fe Bimetallic Nanocomposite for CO 2 Electroreduction.

Surface oxygen vacancies (V o ) regulation is an effective strategy to improve the electrochemical CO 2  reduction reaction (CO 2 RR) performance by lowering the activation energy barrier of CO 2 ; however, the lack of precise control over the local atomic structures severely hinders the large-scale application of V o -activated electrocatalyst for CO 2 RR. Herein, an efficient strategy to facilitate CO 2  activation is developed by introducing V o into transition metal nanoparticles (NPs) with a steam-assisted chemical vapor deposition method. With the steam process, abundant surface V o are introduced into the assembled Ni-Fe bimetallic NPs composite (H-NiFe/NG), which adjust surface Ni/Fe atoms to low-valent coordinatively unsaturated Ni (+1)/Fe (+2) sites, serving as electron-rich centers to adsorb and activate inert CO 2  molecules. The as-prepared H-NiFe/NG composite exhibits excellent catalytic performance with a maximum Faradaic efficiency of 94% at -0.80 V (vs RHE) for CO production with remarkable stability. The density function theory calculations corroborate that the Ni atoms around surface V o significantly lower the energy barrier for COOH* intermediate formation, which gives a low overpotential for reducing CO 2  to CO, exhibiting superior CO 2 RR performance. This general synthetic strategy provides a new insight to introduce surface V o on transition metal for efficient CO 2  reduction.