Defect Engineering of Cobalt-Based Materials for Electrocatalytic Water Splitting

Abstract

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 Coimplicated electrocatalysts are proposed.

Three‐Dimensional Assembly of Iron Phosphide Nanosheets: Synthesis and Enhanced Catalytic Activity for Hydrogen Evolution Reaction

“…The crystallinity of the as‐synthesized FeP x , as characterized by the XRD, is low, which means a large amount of defects in FeP x . The defects one side would act as active sites, and the other side promote the conductivity, thus facilitating the HER reaction . From the XRD patterns of FeO X −Im, FeP x −Im, Fe 2 O 3 −Ca and FeP x −Ca (Figure S8), a weak crystallized FeP phase formed in FeP x −Im after the phosphidation of the weakly crystallized FeO x −Im, while for FeP x −Ca, except for a weakly crystallized FeP phase, a well crystallized Fe 3 O 4 phase exists, indicating only a surface phosphidation for the large crystalline grains of the Fe 2 O 3 −Ca.…”

“…In Figure 3c, The peaks located at 725 and 713 eV can be assigned to Fe 3 + and the peaks located at 723 and 711 eV are ascribed to Fe 2 + , [21] which arise from the superficial oxidation of FeP x under air atmosphere. [22] In addition, the peaks located at 720 and 707 eV should be attributed to the FeÀP band in FeP x . [23] Apparently, the strength of FeÀP band in FeP x -350 is the highest among all the samples, suggesting more iron phosphides on surface.…”

Defects Engineering in Photocatalytic Water Splitting Materials

“…Zou's group synthesized ZnO p‐n homojunctions by decorating n‐type oxygen defective ZnO nanoparticles on the surface of p‐type Zn defective ZnO and found ZnO p‐n homojunctions exhibited much more efficient charge transfer and separation than pure type ZnO, which resulted in high photo‐electrochemical water splitting performance (Figure a–6e) . They also reported the synthesis of TiO 2 p‐n homojunctions by in‐situ decorating n‐type oxygen‐defected TiO 2 QDs on p‐type titanium‐defected TiO 2 surface, which exhibited high photocatalytic H 2 generation efficiency . Meng et al.…”

Micropore-Boosted Layered Double Hydroxide Catalysts: EIS Analysis in Structure and Activity for Effective Oxygen Evolution Reactions

“…However, little attention has been paid to the intrinsic properties of LDHs. [20][21][22] It is well-known that the oxidation reaction facilitates the production of a catalytical active phase with the high valence, but in some aspects the process can be hindered by the close-packed basal planes. 3,[23][24][25] The key to promoting the intrinsic catalytic activity of LDHs is to rationally adjust surface properties or increase the number of active sites.…”