Defect Engineering of Cobalt-Based Materials for Electrocatalytic Water Splitting

Water splitting has been considered as one of the most prospective technologies for enhancing sustainable output of hydrogen and reducing the release of carbon dioxide in the 21st century. Much attention has been paid to designing optimal electrocatalysts for water splitting, which includes the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). To date, the most effective water splitting electrocatalysts are still Pt based and Ir or Ru group noble metal materials, which can significantly improve the current density with the presence of a low overpotential. As alternatives to noble metals electrocatalysts, a series of studies have been carried out for cobalt-based electrocatalysts on the strengths of non-noble metal properties over the past years. However, the defect engineering of cobalt-based materials for the water splitting process has not been explained systematically. Herein, we summarize various kinds of defects and their functions based on Co-based materials for OER and HER. The principles of how various defects improved electrocatalytic performance are introduced clearly; then, the vacancies (included anion and cation vacancies) and heteroatomic doping (included nonmetal and metal atomic doping) were introduced systematically. Furthermore, we especially highlight several defect modification electrocatalysts. Finally, difficulties of defects engineering and the future research directions for Co-implicated electrocatalysts are proposed.